69 Questions with Answers and Explanations on Mendelian & Post Mendelian Genetics for Biology Students.
1. Which contribute to the success of Mendel?
(a) qualitative analysis of data
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(b) observation of distinct inherited traits
(c) his knowledge of biology
(d) consideration of one character at one time.
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Answer and Explanation:
1. (c): Consideration of one character at one time contribute to the success of Mendel. Mendel’s contribution was unique because of his methodological approach to a definite problem, use of clear cut variables and application of mathematics (statistics) to the problem. Using pea plants and statistical methods, Mendel was able to demonstrate that traits were passed from each parent inheritance of genes.
2. Two linked genes a and b show 20% recombination, the individuals of a dihybrid cross between ++/+ + x ab/ab shall show gametes
(a) ++ 80 : ab : 20
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(b) ++ 50 : ab : 50
(c) ++ 40 : ab 40 : + a 10 : + b : 10
(d) ++ 30 : ab 30 : + a 20 : + b : 20
Answer and Explanation:
2. (c): Two linked genes a and b show 20% recombination. The individuals of a dihybrid cross between + +/+ + x ab/ab shall show gametes + + 40 : + a 10 : + b : 10
3. A normal green male Maize is crossed with albino female. The progeny is albino because
(a) trait for a albinism is dominant
(b) the albinos have biochemical to destroy plastids derived from green male
(c) plastids are inherited from female parent
(d) green plastids of male mus. have mutated.
Answer and Explanation:
3. (c): normal green male maize is crossed with albino female. The progeny is albino because; plastids are inherited from female parents.
4. tt mates with Tt. What will be characteristic of offspring?
(a) 75% recessive
(b) 50% recessive
(c) 25% recessive
(d) All dominant.
Answer and Explanation:
4. (b): When tt mate with Tt, the characteristics of offspring will be 50% recessive. On mating tt and Tt, 50% individuals are recessive and 50% inhibit heterozygous dominant characteristics.
5. ABO blood group system is due to
(a) Multifactor inheritance
(b) Incomplete dominance
(c) Multiple allelism
(d) Epistasis.
Answer and Explanation:
5. (c): ABO blood group system is due to multiple allelism. A gene can have more than two alleles or allelomorphs, which can be expressed by mutation in wild form in more than one ways. These alleles or allelomorphs make a series of multiple alleles. The mode of inheritance in case of multiple alleles is called multiple allelism. A well known and simplest example of multiple allelism is the inheritance of ABO blood groups in human beings. In human population, 3 different alleles for this character are found – IA IB and 1°. A person is having only two of these three alleles and blood type can be determined.
6. In a genetic cross having recessive epistasis, F2 phenotypic ratio would be
(a) 9:6:1
(b) 15 : 1
(c) 9 : 3 : 4
(d) 12 : 3 : 1.
Answer and Explanation:
6. (c): In a genetic cross having recessive epistasis, F2 phenotypic ratio would be 9:3 :4. The recessive epistasis is illustrated by coat colour in mouse, the coat colour is determined by A/a pair, recessive allele b is epistatic over A/a. Thus, in the presence of bb, both A and aa give the same phenotype (albino). The F2 ratio is generally 9 : 3 : 4.
7. Cross between AaBB and aaBB will form
(a) 1 AaBB : laaBB
(b) All AaBB
(c) 3AaBB : laaBB
(d) 1 AaBB : 3aaBB.
Answer and Explanation:
7. (a): Cross between AaBB and aaBB will form 1 AaBB : 1 aaBB. On crossing, AaBB x aaBB gives 50% individuals having genotype AaBB and 50% individuals having genotype aaBB.
8. RR (Red) Antirrhinum is crossed with white (WW) one. Offspring RW are pink. This is an example of
(a) dominant-recessive
(b) incomplete dominance
(c) hybrid
(d) supplementary genes.
Answer and Explanation:
8. (b): RR (Red) Antirrhinum is crossed with white (ww) one. Offspring RW are pink. This is an example of incomplete dominance. Incomplete dominance may be defined as the partial expression of both alleles in heterozygote so that the phenotype is intermediate between those of homozygotes.
In plants like the Snapdragon (Antirrhinum majus), when a plant bearing red (RR) flowers is crossed with the plant bearing white (it) flowers, the flowers of F, plants were crossed to each other, F2 generation showed red (RR), pink (Rr) and white (rr) flowered plants in the ratio of 1 : 2 :1. Dominance thus appeared to be partial or incomplete.
9. The allele which is unable to express its effect in the presence of another is called
(a) co dominant
(b) supplementary
(c) complementary
(d) recessive.
Answer and Explanation:
9. (d): The allele which is unable to express its effect in the presence of another is called recessive. A member of a pair of alleles that does not show its effect in the phenotype in the presence of any other allele. It is denoted by small letter.
10. Blue eye colour is recessive to brown eye colour. A brown eyed man whose mother was blue eyed marries a blue-eyed woman. The children will be
(a) both blue eyed and brown eyed 1 : 1
(b) all brown eyed
(c) all blue eyed
(d) blue eyed and brown eyed 3:1.
Answer and Explanation:
10. (a): Blue eye colour is recessive to brown eye colour. A brown eyed man whose mother was blue eyed marries a blue eyed woman. The children shall be both blue eyed and brown eyed 1:1. The brown eyed man will have the genotype Bb and his wife bb. Hence Bb x bb = Bb: bb. Hence, the ratio is 1 : 1.
11. A dihybrid condition is
(a) segregation
(b) dominance
(c) independent assortment
(d) polygenic inheritance.
Answer and Explanation:
11. (d): A dihybrid condition is TtRr. Dihybrid conditions involves simultaneous inheritance of two pairs of mendelian factors or genes.
12. Mendel’s last law is
(a) segregation
(b) dominance
(c) independent assortment
(d) polygenic inheritance.
Answer and Explanation:
12. (c): Mendel’s last law is independent assortment. The principle of independent assortment states that when two individuals differ from each other in two or more pairs of factors, the inheritance of one pair is quite independent of the inheritance of ethers.
13. First geneticist/father of genetics was
(a) De Vries
(b) Mendel
(c) Darwin
(d) Morgan.
Answer and Explanation:
13. (b): An Australian Monk, Gregor Mendel, developed his theory of in heritance. He formulated the law of Heredity. Therefore, he is called the ‘father of genetics’.
14. The contrasting pairs of factors in Mendelian crosses are called
(a) multiple alleles
(b) alloloci
Answer and Explanation:
14. (b): The contrasting pairs of factors in Mendelian crosses are called allelomorphs. Alleles or allelomorphs are the different forms of a gene, having the same locus on homologous chromosomes and are subject to mendelian (alternative) inheritance.
15. Multiple alleles control inheritance of
(a) phenylketonuria
(b) colour blindness
(c) sickle cell anaemia
(d) blood groups.
Answer and Explanation:
15. (d): ABO blood group system is due to multiple allelism. A gene can have more than two alleles or allelomorphs, which can be expressed by mutation in wild form in more than one ways.
These alleles or allelomorphs make a series of multiple alleles. The mode of inheritance in case of multiple alleles is called multiple allelism. A well known and simplest example of multiple allelism is the inheritance of ABO blood groups in human beings. In human population, 3 different alleles for this character are found – IA IB and 1°. A person is having only two of these three alleles and blood type can be determined.
16. A man of A-blood group marries women of AB blood group. Which type of progeny would indicate that man is heterozygous A?
(a) AB
(b) A
(c) O
(d) B.
Answer and Explanation:
16. (d): IAI° x 1AIB gives us the following genotypes IAIA, I°IB, IAIB. Hence, when a man of blood group A marries a women of AB blood group, B progeny would indicate that man is heterozygous A.
17. An organism with two identical alleles is
(a) dominant
(b) hybrid
(c) heterozygous
(d) homozygous.
Answer and Explanation:
17. (d): An organism with two identical alleles is homozygous. Homozygous have identical genes at the same locus on each member of a pair of homologous/ chromosomes.
18. Segregation of Mendelian factors (no linkage, no crossing over) occurs during
(a) anaphase I
(b) anaphase II
(c) diplotene
(d) metaphase I.
Answer and Explanation:
18. (a): Segregation of Mendelian factors (no linkage, no crossing over) occurs during anaphase I. At anaphase I, actual segregation occurs, but two similar alleles occurs in the dyad chromosome which separate at anaphase II.
19. In a cross between AABB x aabb, the ratio of F2 genotypes between AABB, AaBB, Aabb and aabb would be
(a) 9 : 3 : 3 : 1
(b) 2 : 1 : 1 : 2
(c) 1 : 2 : 2 : 1
(d) 7 : 5 : 3 : 1.
Answer and Explanation:
19. (c): In a cross between AABB x aabb, the ratio of F2 genotypes between AABB, AaBB, Aabb and aabb would be 1 : 2 : 2 : 1. Genotype is the genetic makeup of an individual. This may refer to just one trait or it may refer to the combination of many or all of the traits of the individuals.
20. A gene pair hides the effect of another. The phenomenon is
(a) epitasis
(b) dominance
(c) mutation
(d) none of these.
Answer and Explanation:
20. (a): A gene pair hides the effect of another. The phenomenon is epistasis. When one gene modifies or masks the action of another gene. This is known as epistasis, and it can give rise to unusual ratios in genetic crosses. The gene, which can override the expression of the other, is the epistasis gene and the other, which get masked, is the hypostatic gene.
21. An allele is dominant if it is expressed in
(a) both homozygous and heterozygous states
(b) second generation
(c) heterozygous combination
(d) homozygous combination.
Answer and Explanation:
21. (a): An allele is dominant if it is expressed in both homozygous states. Dominant alleles expresses itself in the homozygous as well as heterozygous condition. It is denoted by capital letter.
22. A child of O-group has B-group father. The genotype of father will be
(a) I°I°
(b) IBIB
(c) IAIB
(d) IBI°.
Answer and Explanation:
22. (d): The child of O-group has B-group father. The genotype of father will be IBI°. The genotype of the child would be I°I° (recessive). Hence, the genotype of the father can only be IBI°.
23. Mendel studied inheritance of seven pairs of traits in Pea which can have 21 possible combinations.
If you are told that in one of these combinations, independent assortment is not observed in later studies, your reaction will be
(a) independent assortment principle may be wrong
(b) mendel might not have studied all the combinations
(c) it is impossible
(d) later studies may be wrong.
Answer and Explanation:
23. (b): Law of independent assortment states that when two individuals differ from each other in two or more pairs of factors, the inheritance of one pair is quite’ independent of the inheritance of other. Law of independent assortment is applicable to only those factors or genes which are located on different chromosomes.
24. A polygenic inheritance in human beings is
(a) skin colour
(b) phenylketonuria
(c) colour blindness
(d) sickle cell anaemia.
Answer and Explanation:
24. (a): A polygenic inheritance in human beings is skin colour. Polygenic or quantitative inheritance occurs when several genes occupying different loci on the same homologous pairs of chromosomes govern one tract. Inheritance of colour in man is an example of polygenic inheritance. The presence of melanin pigment in the skin colour. The more the pigment the darker is the skin.
25. Two dominant nonallelic genes are 50 map units apart. The linkage is
(a) cis type
(b) trans type
(c) complete
(d) absent/incomplete.
Answer and Explanation:
25. (d): Two dominant nonallelic genes are 50 map units apart. The linkage is absent/incomplete. Chromosome mapping is based on the fact that genes are linearly arranged in the chromosome and frequency of crossing over is directly proportional to the distance between two genes. Dominant genes show cis arrangement. At 50 map units cis is changed to trans and vice-versa hence no fixed linkage is present.
26. Of a normal couple, half the sons are haemophiliac while half the daughters are carriers. The gene is located on
(a) X-chromosome of father
(b) Y-chromosome of father
(c) one X-chromosome of mother
(d) both the X-chromosomes of mother.
Answer and Explanation:
26. (c): Of a normal couple, half the sons are haemophilic while half the daughters are carries. The gene is located on one X-chromosomes of mother. Cross between a haemophilic carrier female XhX and normal male would yield 50% of the sons being haemophilic and 50% of the daughter are carriers.
27. Which of the following is suitable for experiment on linkage?
(a) aaBB x aaBB
(b) AABB x aabb
(c) AaBb x AaBb
(d) AAbb x AaBB.
Answer and Explanation:
27. (b): AABB x aabb is suitable for experiment on linkage. Linkage is the tendency for certain genes tend to be inherited together, because they are on the same chromosome. Thus, parental combinations of characters are found more frequently in offspring than non-parental.
28. Mr. Kapoor has Bb autosomal gene pair and d allele sex-linked. What shall be proportion of Bd in sperms?
(a) zero
(b) 1/2
(c) 1/4
(d) 1/8.
Answer and Explanation:
28. (c): Genotype of Mr. Kapoor will be Bbd hence one fourth of the sperms will have Bd.
29. Of both normal parents, the chance of a male child becoming colour blind are
(a) no
(b) possible only when all the four grand parents had normal vision
(c) possible only when father’s mother was colour blind
(d) possible only when mother’s father was colour blind.
Answer and Explanation:
29. (d): Of both normal parents, the chance of a male child becoming colour blind are possible only when mother’s father was colour blind. It is an example of criss cross inheritance. If a cross is made between two sexes differing in certain characters, in such a way that character of one sex remains hidden in the opposite sex of F, generation, but it is passed on to the same sex in the F, generation, it is said to exhibit criss cross inheritance.
30. The phenomenon, in which an allele of one gene suppresses the activity of an allele of another gene, is known as
(a) epistasis
(b) dominance
(c) suppression
(d) inactivation.
Answer and Explanation:
30. (a): Epistasis is the phenomenon by which a gene suppresses the phenotypic expression of a nonal leiic gene. In this type of interaction one gene masks or changes the
Effect of another gene. This is a counterpart of dominance. While dominance works at interallelic but interagenic level, epistasis works at intergenic level.
31. When two genetic loci produce identical phenotypes in cis and trans position, they are considered to be
(a) multiple alleles
(b) the parts of same gene
(c) pseudoalleles
(d) different genes.
Answer and Explanation:
31. (c): E.B. Lewis in 1951 reported from a cross of apricot eyed and white eyed flies in Drosophila, he obtained F1 having intermediate eye colour. In F2, he had expected segregation only for apricot and white, but he recovered very low frequency of wild type. Since those alleles behaved as non-alleles, Lewis preferred to call them pseudoalleles and the phenomenon as pseudoallelism.
In pseudoallelism in cis position both the mutant alleles are on one chromosome. So the other chromosome will be normal and will be able to produce the end result. But in trans position the sequence of steps involved in synthesis will be interrupted due to mutations on either of the two homologous chromosomes thus leading to a mutant phenotype.
32. When two dominant independently assorting genes react with each other, they are called
(a) collaborative genes
(b) complementary genes
(c) duplicate genes
(d) supplementary genes.
Answer and Explanation:
32. (b): Complementary genes are those nonallelic genes which independently show a similar effect but produce a new trait when present together in the dominant form. Supplementary genes are a pair of nonallelic a gene, one of which produce its effect independently in the dominant state while the dominant allele of the second gene is without any independent effect but is able to modify the effect of the former to produce a new trait. Duplicate genes are independent genes producing the same or similar effect.
33. The polygenic genes show
(a) different karyotypes
(b) different genotypes
(c) different phenotypes
(d) none of these.
Answer and Explanation:
33. (c): Polygenes are also called multiple factor. Polygene is a gene with an individually small effect on the phenotype that interacts with other polygenes controlling the same character to produce the continuous quantitative variation typical of such traits as height, weight and skin colour.
34. A fruit fly is heterozygous for sex-linked genes, when mated with normal female fruit fly, the males specific chromosome will enter egg cell in the proportion
(a) 3 : 1
(b) -7:1
(c) 1:1
(d) 2.: 1.
Answer and Explanation:
34. (c): The female Drosophila possesses two homomorphic sex chromosomes, (XX) and the male Drosophila contains two heteromorphic sex chromosomes (XY). The differential or non-homologous region of Y-chromosome is mostly heterochromatic. The female parent produces only one type of eggs (22 + X).
The male parent produces two types of gametes (22 + Y) and (22 + X). They are produced in equal proportions. As the two types of sperms are produced in equal proportions, there are equal chances of getting a male or female fly in a particular mating.
35. How many different types of genetically different gametes will be produced by a heterozygous plant having the genotype AABbCc?
(a) six
(b) nine
(c) two
(d) four.
Answer:
(d) four.
36. Crossing over in diploid organism is responsible for
(a) segregation of alleles
(b) recombination of linked alleles
(c) dominance of genes
(d) linkage between genes.
Answer and Explanation:
36. (b): Crossing over is the reciprocal exchange of segments between nonsister chromatids of a pair of homologous chromosomes. It results in recombination of genes.
The nonsister chromatids in which exchange of segments takes place are known as cross-overs or recombinants while other chromatids not involved in exchange of segments are called noncross-over or parental types. Single crossing-over at one point between two nonsister chromatids resulting in two cross-over and two parental types. Double crossing over at two points in a tetrad of chromatids.
37. If Mendel had studied the seven traits using a plant with 12 chromosomes instead of 14, in what way would his interpretation have been different?
(a) he would not have discovered the law of independent assortment
(b) he would have discovered sex linkage
(c) he could have mapped the chromosome
(d) he would have discovered blending or incomplete dominance.
Answer and Explanation:
37. (a): According to principle of independent assortment, the two factors of each trait assort at random and independent of the factors of other traits at the time of meiosis and get randomly as well as independently rearranged in the offspring. Principle of independent assortment is applicable to only those factors or genes which are present on different chromosomes. Chromosomes have hundreds of genes which show linked inheritance or linkage. Linkage is the phenomenon of certain genes (present on the same chromosome) to remain together and get inherited through generations. The seven characters that Mendel chooses were present on 14 chromosomes and so they did not show linkage but if present on 12 chromosomes they would have shown linkage and the principle of independent assortment would not have been discovered.
38. When a single gene influences more than one trait it is called
(a) pseudodominance
(b) pleiotrophy
(c) epistasis
(d) none of these.
Answer and Explanation:
38. (b): The ability of a gene to have multiple phenotypic effect because it influences a number of characters simultaneously is known as pleiotrophy. The phenomenon by which a gene suppresses the phenotypic expression of a nonallelic gene is called epistasis.
39. In hybridization, Tt x tt gives rise to the progeny of ratio
(a) 2 : 1
(b) 1 : 2 : 1
(c) 1:1
(d) 1 : 2.
Answer:
(c) 1:1
40. A gene pair hides the effect of another gene. The phenomenon is called
(a) dominance
(b) segregation
(c) epistasis
(d) mutation.
Answer and Explanation:
40. (c): Epistasis is the phenomenon of suppression of phenotypic expression of gene by a nonallelic gene which shows its own effect. The gene which masks the effect of another is called epistatic gene while the one which is suppressed is termed hypostatic gene. Epistasis is of three types – dominant, recessive and dominant-recessive. The epistatic ratio is 12: 3: 1.
41. According to mendelism which character shows dominance?
(a) terminal position of flower
(b) green colour in seed coat
(c) wrinkled seeds
(d) green pod colour.
Answer:
(d) green pod colour.
42. Due to the cross between TTRrxttrr the resultant progenies show what percent of tall, red flowered plants
(a) 50%
(b) 75%
(c) 25%
(d) 100%.
Answer:
(a) 50%
43. Independent assortment of genes does not takes place when
(a) genes are located on homologous chromosomes
(b) genes are linked and located on same chromosome
(c) genes are located on non-homogenous chromosome
(d) all the above.
Answer and Explanation:
43. (b): According to the principle of law of independent assortment the two factors of each trait assort at random and independent of the factors of other traits at the time of meiosis and get randomly as well as independently rearranged in the offspring. Principle of law of independent assortment is applicable to only those factors or genes which are present on different chromosomes.
44. Ratio of complementary genes is
(a) 9:3:4
(b) 12 : 3 : 1
(c) 9 : 3 : 3 : 4
(d) 9 : 7.
Answer and Explanation:
44. (d): If two genes present on different loci produce the same effect when present alone but interact to form a new trait when present together, they are called complementary genes. The F2 ratio is modified to 9: 7 instead of 9: 3: 3: 1.
45. When dominant and recessive alleles express itself together it is called
(a) co-dominance
(b) dominance
(c) amphidominance
(d) pseudo dominance.
Answer and Explanation:
45. (a): Dominance is the phenomenon in which one member of a pair of allelic genes expresses itself as a whole (complete dominance) or in part (incomplete dominance).
Co dominance is when the two genes neither show dominant-recessive relationship nor show intermediate condition, but both of them express themselves simultaneously. This has been reported in roan character of cattle (i.e., patches of 2 different colours on the skin). Pseudo dominance is when a recessive allele of normal homologous chromosome will behave like a dominant allele and will be phenotypically expressed.
46. A and B genes are linked. What shall be genotype of progeny in a cross between AB/ab and ab/ab
(a) AAbb and aabb
(b) AaBb and aabb
(c) AABB and aabb
(d) none of the above.
Answer:
(b) AaBb and aabb
47. Two nonallelic a gene produces the new phenotype when present together but fail to do so independently then it is called
(a) epistasis
(b) polygene
(c) non complementary gene
(d) complementary gene.
Answer and Explanation:
47. (a): Epistasis is the phenomenon of suppression of phenotypic expression of gene by a nonallelic gene which shows its own effect. The gene which masks the effect of another is called epistatic gene while the one which is suppressed is termed hypostatic gene. Epistasis is of three types – dominant, recessive and dominant-recessive. Two or more different pairs of alleles, with a presumed cummulative effect governing quantitive traits like size, pigmentation etc., are called polygenes.
48. A gene is said to be dominant if
(a) it expresses its effect only in homozygous state
(b) it expresses its effect only in heterozygous condition
(c) it expresses its effect both in homozygous and heterozygous condition.
(d) it never expresses its effect in any condition.
Answer:
(c) it expresses its effect both in homozygous and heterozygous condition.
49. On selfing a plant of F1 generation with genotype “AABbCC”, the genotypic ratio in F2-generation will be
(a) 3 : 1
(b) 1 : 1
(c) 9:3:3:1
(d) 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1.
Answer and Explanation:
49. (a): Selfing is the process of fertilization with polar or male gametes of the same individual. AABbCC will produce two type of gametes ABC and AbC. Thus in F2 generation three genotypes will be obtained. These are AABBCC, AABbCC and AAbbCC in the ratio of 1: 2: 1. Phenotypically AABBCC and AABbCC are same. So the phenotypic ratio in F2 generation will be 3: 1.
50. There are three genes a, b, c. Percentage of crossing over between a and b is 20%, b and c is 28% and a and c is 8%. What is the sequence of genes on chromosome?
(a) b, a, c
(b) a, b, c
(c) a, c, b
(d) none of these.
Answer and Explanation:
50. (a): Crossing over and recombination frequencies : One crossing over produces 50% recombinant types. Therefore, frequency of crossing over would be double the frequency of recombinants. 1% recombinants (1% cross-over) mean crossing over in 2% meiocytes. Linkage/ Cross over/ Chromosome maps is a graphic representation of relative positions/ order and relative distances of genes in a chromosome in the form of line like a linear road map depicting different places and their relative distances without giving exact mileage.
It is based on Morgan’s hypothesis (1911) that frequency of crossing over/recombination between two linked genes is directly proportional to the physical distance between the two. 1 map unit or centrimorgan is equivalent 1% recombination between two genes. Percentage of crossing over between a and b is 20% so they are 20 map distance apart and b and c are 28 map distance apart. So that corrects sequence of genes chromosomes will be as
20 8 b– a ————— c
51. Which of the following is an example of pleiotropy ?
(a) haemophilia
(b) thalassemia
(c) sickle cell anaemia
(d) colour blindness.
Answer and Explanation:
51. (c): Pleiotropic gene is such a gene which has a wider effect on phenotype i.e., it controls several phenotypic traits. Sickle cell anaemia is considered to be caused by one such pleiotropic gene.
Sickle cell anaemia is caused due to a mutation in P globin gene of haemoglobin. Single point mutation leads to one change of amino acid. Hb P chain 1 2 345678 i
Glutamic acid (normal)
Valine (after mutation)
But this small point mutation & change in the resulting P globin loads to sickling of RBCs, haemolytic anaemia, pain in joints, splenomegaly etc.
Moreover carrier of sickle cell anaemia gene remains protected from malaria. Thus the gene is naturally selected in tropical & subtropical Asia and Africa.
52. Two crosses between the same pair of genotypes or phenotypes in which the sources of the gametes are reversed in one cross, is known as
(a) test cross
(b) reciprocal cross
(c) dihybrid cross
(d) reverse cross
Answer and Explanation:
52. (b): A reciprocal cross means that the same two parent are used in two experiments in such a way that if in one experiment A is used as the female parent and B is used as the male parent then in the other experiment A will be used as the male parent and B as the female parent. Thus the sources of gametes are reversed. When the F, individuals obtained in a cross is crossed with the recessive parent is called a test cross. When inheritance of two pairs of contrasting character is studied simultaeneously it is called dihybrid cross.
53. The genes controlling the seven pea characters studied by Mendel are now known to be located on how many different chromosomes?
(a) seven
(b) six
(c) five
(d) four
Answer and Explanation:
53. (d): Mendel worked on garden pea. He chose only those characters which showed consistent results. He worked on seven characters. These characters showed complete independent assortment despite the seven characters chosen by him were present on four chromosomes -1, 4, 5 and 7.
54. Which one of the following traits of garden pea studied by Mendel was a recessive feature?
(a) axial flower position
(b) green seed colour
(c) green pod colour
(d) round seed shape
Answer and Explanation:
54. (b): Mendel worked on garden pea and choose seven characters for this. Green seed colour is the recessive character in his experiment and the dominant character for seed colour is yellow. Axial flower position, green pod colour and round seed shape are all dominant characters.
55. One of the parents of a cross has a mutation in its mitochondria. In that cross, that parent is taken as a male. During segregation of F2 progenies that mutation is found in
(a) one-third of the progenies
(b) none of the progenies
(c) all the progenies
(d) fifty percent of the progenies.
Answer and Explanation:
55. (b): Mutation is a sudden alteration of the chemical structure of a gene or the alteration of its position on the chromosome by breaking and rejoining of the chromosome. It has occurred in male parent. But organelles like mitochondria, chloroplast etc. are a part of cytoplasmic inheritance.
Cytoplasmic inheritance is the passage of traits from parents to offspring through structures present inside the cytoplasm of contributing gametes. Plasma genes occur in plastids, mitochondria, plasmids and some special particles like kappa particles, sigma particles, etc.
In higher organisms cytoplasmic inheritance is called maternal inheritance because the zygote receives most of its cytoplasm from the ovum. Therefore, cytoplasmic inheritance is usually unparental. “=n none of the progeny will show mutation as the mutation is male in mitochondria.
56. Lack of independent assortment of two genes A and B in fruit fly Drosophila is due to
(a) repulsion
(b) recombination
(c) linkage
(d) crossing over.
Answer and Explanation:
56. (c): Mendel’s law of independent assortment states that when the parent differs from each other in two or more pairs of contrasting characters, the inheritance of one pair of factor is independent of the other. For the character to assort independently they should be located on separate non homologous chromosomes. Genes present on the same chromosome show linkage.
It means that these characters remain together and thus low numbers of combinations are formed. This phenomenon is called linkage such genes are called linked genes. So A and B are linked genes.
57. A male human is heterozygous for autosomal genes A and B and is also hemizygous for hemophilic gene h. What proportion of his sperms will be abh?
(a) 1/8
(b) 1/32
(c) 1/16
(d) 1/4.
Answer and Explanation:
57. (a): The male human is heterozygous for autosomal gene A and B and also hemizygous for hemophilic gene h then his genotype will be AaBbXhY because hemophilia is a sex linked trait that is present an X-chromosome. So the total number of gametes will be abXh, abY, ABXh, ABY, AbXh, AbY, aBX aBY. So the proportion of abXh sperm will be 1/8.
58. A nutritionally wild type organism, which does not required any additional growth supplement is known as
(a) phenotype
(b) holotype
(c) autotroph
(d) prototroph.
Answer and Explanation:
58. (d): Prototroph is the nutritionally wild strain which is unable to grow in the minimal medium unless additional nutrients were added to the medium. Phenotype is the kind of organism produced by the reaction of a given genotype with the environment. Holotype is one of the original type used to describe a new species.
59. In a plant, red fruit (R) is dominant over yellow fruit (r) and tallness (7) is dominant over shortness (t). If a plant with RRTt genotype is crossed with a plant that is rrtt,
(a) 25% will be tall with red fruit
(b) 50% will be tall with red fruit
(c) 75% will be tall with red fruit
(d) all the offspring will be tall with red fruit.
Answer:
(b) 50% will be tall with red fruit
60. In order to find out the different types of gametes produced by a pea plant having the genotype AaBb it should be crossed to a plant with the genotype
(a) AABB
(b) AaBb
(c) aabb
(d) aaBB.
Answer and Explanation:
60. (c): A test cross involving the crossing of F, individual with the homozygous recessive parent. It is done to find out homozygous and heterozygous individuals. So AaBb, should be crossed with aabb.
61. Which one of the following is an example of polygenic inheritance?
(a) skin colour in humans
(b) flower colour in Mirabilis jalapa
(c) production of male honey bee
(d) pod shape in garden pea
Answer and Explanation:
61. (a): Quantitative or polygenic inheritance is that type of inheritance in which the complete expression of a trait is controlled by two or more genes in which a dominant allele of each gene contributes only a unit fraction of the trait and the total phenotypic expression is the sum of total effect of all the dominant alleles of genes/polygenes. The complete trait developes only by the cumulative effect of all homologous and nonhomologous dominant alleles influencing that trait. Human skin colour (melanin) is controlled by three pairs of polygenes A, B and C.
62. Phenotype of an organism is the result of
(a) genotype and environment interactions
(b) mutations and linkages
(c) cytoplasmic effects and nutrition
(d) environmental changes and sexual dimorphism
Answer and Explanation:
62. (a): The external manifestation, morphological or physiological expression of an individual with regard to one or more characters is cali-d phenotype. For recessive genes, phenotype and genotype are similar. For dominant genes, the phenotype is same for both homozygous states. Phenotype is influenced by environment as well as age.
A child definitely differs from adolescent, the latter from adult and ar. adult from aged one. Many phenotypes are determined by multiple genes. Thus, the identity of phenotype is determined by genotype and environment.
63. How many different kinds of gametes will be produced by a plant having the genotype AABbCC?
(a) two
(b) three
(c) four
(d) nine
Answer:
(a) two
64. In Mendel’s experiments with garden pea, round seed shape (RR) was dominant over wrinkled seeds (rr), yellow cotyledon (YY) was dominant over green cotyledon (yy). What are the expected phenotypes in the F2 generation of the cross RRYY x rryy?
(a) round seeds with yellow cotyledons, and wrinkled seeds with yellow cotyledons
(b) only round seeds with green cotyledons
(c) only wrinkled seeds with yellow cotyledons
(d) only wrinkled seeds with green cotyledons
Answer:
(a) round seeds with yellow cotyledons, and wrinkled seeds with yellow cotyledons
65. Test cross involves
(a) crossing between two genotypes with dominant trait
(b) crossing between two genotypes with recessive trait
(c) crossing between two F, hybrids
(d) crossing the F, hybrid with a double recessive genotype
Answer and Explanation:
65. (d): Test cross is obtained when F, plant is crossed with homozygous recessive individual. By this cross the heterozygocity and homozygocity of the organisms can be tested. The offsprings will be 100% dominant if the individual was homozygous dominant, the ratio will be 50% dominant and 50% recessive in case of hybrid or heterozygous individual.
66. A common test to find the genotype of a hybrid is by
(a) crossing of one F2 progeny with female parent
(b) studying the sexual behaviour of F. progenies
(c) crossing of one F, progeny with male parent
(d) crossing of one F2 progeny with male parent.
Answer and Explanation:
66. (c): A common test to find the genotypes of a hybrid is by crossing of one F, progeny with male parent.
67. In the hexaploid wheat, the haploid («) and basic (a–) numbers of chromosomes are
(a) n = 21 and r = 21
(b) rx = 21 and jc = 14
(c) n = 21 and = 7
(d) n = 7 and x = 2.
Answer and Explanation:
67. (c): Hexaploid wheat is a result of allopolyploidy induced by doubling the chromosome number of the hybrid produced by crossing two different plants. In hexaploid wheat triticale 2m = 6x = 42. So x stands for basic chromosome number and n for haploid chromosome number. So, n- 21 and x = l for hexaploid wheat.
68. Inheritances of skin colour in humans is an example of
(a) point mutation
(b) polygenic inheritance
(c) codominance
(d) chromosomal aberration.
Answer and Explanation:
68. (b): Polygenic inheritance is that type of inheritance in which the complete expression of a trait is controlled by two or more genes in which a dominant allele of each gene contribution only a unit fraction of the trait and total phenotypic expression is the sum total of a additive or cumulative effect of all the dominant alleles of genes/polygenes. Human skin colour is an example of such polygenic inheritance which is controlled by three pairs of polygenes A, B and C. Negro/black colour is due to presence of all the six dominant contributing alleles AABBCC. Very light colour or white olour is due to presence of all six recessive noncontributing alleles aabbcc.
69. In pea plants, yellow seeds are dominant to green. If a heterozygous yellow seeded plant is crossed with a green seeded plant, what ratio of yellow and green seeded plants would you expect in F[ generation?
(a) 9 : 1
(b) 1 : 3
(c) 3 : 1
(d) 50 : 50
Answer:
(d) 50 : 50
