Biology

Genetics and Plant Breeding

1,177 Questions

Genetics and Plant Breeding explores the principles of heredity, chromosomal inheritance, and hybridization techniques. It includes key concepts like Mendelian genetics, gene linkage, and polygenic inheritance. This topic is essential for students tackling advanced biology or botany sections in competitive examinations.

Mendelian InheritanceChromosome TheoryGene LinkagePolygenic InheritancePlant HybridizationPopulation Genetics Equilibrium

Genetics and Plant Breeding Questions

Multiple choice

Which of the following statements is/are false?

a. Blonde hair is a phenotype produced by the genotype HH or Hh. b. The dihybrid cross is the inheritence of two pairs of contrasting characteristics of plants such as round-yellow seeds and wrinkled-green seeds. c. The male and female gamete carry one gene for each characteristic from the gene pairs of parents.

  1. Only a

  2. Only a and b

  3. Only b

  4. Only b and c

  5. Only c
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is the correct option as this statement is false. Blonde hair is a phenotype produced by the genotype hh.

Multiple choice

Match the following:

 
a. Gene 1. It is the description of genes present in an organism.
b. Genotype 2. It is a unit of heridity that transfers characteristics from parents to their offsprings during reproduction.
c. Phenotype 3. It is the trait that is visible in an organism.

  1. a - 2, b - 1, c - 3

  2. a - 2, b - 3, c - 1

  3. a - 1, b - 3, c - 2

  4. a - 1, b - 2, c - 3

  5. a - 3, b - 1, c - 2
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is the correct option. Gene is a unit of heridity that transfers characteristics from parents to their offsprings during reproduction. Genotype is the description of genes present in an organism. Phenotype is the trait that is visible in an organism.

Multiple choice

Which of the following are correct about sex-linked recessive inheritance? P. Most affected individuals are males. Q. Affected females come from affected fathers and affected or carrier mothers. R. The sons of affected females should be affected. S. The trait does not skip generations.

  1. P and S

  2. P, Q and R

  3. Q, R and S

  4. P, Q, R and S
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In X-linked recessive inheritance, males are primarily affected because they have only one X chromosome. Affected females require an affected father and a carrier or affected mother to inherit two recessive alleles. Sons of affected females always receive the X chromosome with the recessive allele and will be affected. These traits can skip generations through carrier females, so S is false.

Multiple choice

Hemophilia is a recessive X-linked trait in humans. If a heterozygous woman has children with a normal man, what are the odds of the following combinations of children? P. An unaffected daughter or son Q. Two out of five offsprings that are affected

  1. P - 1/4 and Q - 52.6%

  2. P - 3/4 and Q - 26.3%

  3. P - 3/4 and Q - 50%

  4. P - 81/256 and Q - 26.3%
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For a heterozygous female (X^H X^h) crossed with a normal male (X^H Y): each child has 1/4 chance of being unaffected (X^H X^H female or X^H Y male). So P (unaffected) = 3/4. For 5 offspring, the probability exactly 2 are affected is calculated using binomial distribution: C(5,2) × (1/4)^2 × (3/4)^3 = 10 × 1/16 × 27/64 ≈ 26.3%.

Multiple choice

Which of the following is not true about autosomal dominant traits?

  1. Every affected person should have at least one affected parent.

  2. Males and females should be equally often affected.

  3. An affected person has a 50% chance of transmitting the dominant allele to each offspring.

  4. All the daughters of an affected male will be affected but none of the sons.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For autosomal dominant traits, every affected individual must have an affected parent (except new mutations), males and females are equally affected, and there's a 50% transmission risk to each offspring. However, both sons AND daughters of an affected male have equal 50% chance - not all daughters and no sons. This sex-specific pattern describes X-linked inheritance, not autosomal dominant.

Multiple choice

Which statement about allele frequencies is not true?

  1. The sum of any set of allele frequencies is always 1.

  2. If there are two alleles at a locus and we know the frequency of one of them, we can obtain the frequency of the other by subtraction.

  3. If an allele is missing from a population, its frequency is 0.

  4. If two populations have the same allele frequencies at a locus, they must have the same proportion of homozygotes at that locus.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Allele frequencies always sum to 1, and if there are two alleles, knowing one frequency gives the other. A missing allele has frequency 0. However, two populations can have identical allele frequencies but different homozygote proportions because the frequencies themselves don't determine homozygosity - you need to know whether the population is in Hardy-Weinberg equilibrium to make that calculation.

Multiple choice

Which of the following are correct? P. Classical Mendelian traits are qualitative in nature. Q. Qualitative traits show discontinuous variations. R. Qualitative traits are polygenic traits. S. Qualitative traits are referred to as metric traits.

  1. P and Q

  2. P and S

  3. Q and R

  4. R and S
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Classical Mendelian traits are qualitative and show discontinuous variation (distinct categories like tall vs short). They are typically monogenic (controlled by one or few genes), not polygenic. Polygenic traits show continuous variation and are called quantitative or metric traits, not qualitative.

Multiple choice

If A/A/.B/B is crossed to the a/a.b/b, and the F1 is test crossed. What percent of the test cross progeny will be a/a.b/b if the two genes are P. unlinked Q. completely linked (no crossing over at all) R. 10 map units apart S. 24 map units apart

  1. P – 0%, Q – 0%, R – 38%, S – 45%

  2. P – 25%, Q – 50%, R – 45%, S – 38%

  3. P – 0%, Q – 25%, R – 45%, S – 38%

  4. P – 25%, Q – 0%, R – 38%, S – 45%
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For test cross of AaBb: P (unlinked) - parental aabb is 1/4 (25%). Q (completely linked) - aabb requires no crossover, so 50% parental types. R (10 map units) - 10% recombinants, so aabb = 45% parental. S (24 map units) - 24% recombinants, so aabb = 38% parental. The further apart the genes, the more crossing over, so fewer parental aabb progeny.

Multiple choice

Two genes are located on the same chromosome and are known to be 12 map units apart. An AABB individual is crossed to an aabb individual to produce AaBb offspring. The AaBb offsprings are then crossed to aabb individuals. If this cross produces 1000 offsprings, what is the predicted number of offsprings with each of the four genotypes: AaBb, Aabb, aaBb and aabb?

  1. 60 Aabb, 440 aaBb, 440 AaBb and 60 aabb

  2. 0 Aabb, 0 aaBb, 440 AaBb and 440 aabb

  3. 440 Aabb, 440 aaBb, 60 AaBb and 60 aabb

  4. 60 Aabb, 60 aaBb, 440 AaBb and 440 aabb
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The genes are 12 map units apart, so the recombination frequency is 12%. Parental gametes (AB and ab) occur 88% of the time (44% each), while recombinant gametes (Ab and aB) occur 12% of the time (6% each). When AaBb is crossed with aabb, we get 440 AaBb, 440 aabb, 60 Aabb, and 60 aaBb.

Multiple choice

In Drosophila melanogaster, cherub wings (ch), black body (b) and cinnabar eyes (cn) are recessive to their corresponding alleles (represented as ch+, b+ and cn+, respectively) and are all located on chromosome 2. Homozygous wild type flies were mated with cherub, black and cinnabar flies and the resulting F1 females were test crossed with cherub, black and cinnabar males. The following progenies were produced from the test cross: ch b+ cn 110 ch+ b+ cn+ 780 ch+ b cn 70 ch+ b+ cn 6 ch b cn 769 ch b+ cn+ 60 ch+ b cn+ 111 ch b cn+ 9 Total 1915 Of these three genes, which one is in the middle?

  1. The locus that determines cherub wings

  2. The locus that determines cinnabar eyes

  3. The locus that determines black body

  4. Cannot be determined

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In a three-point cross, the double crossover classes have the lowest frequency. Here, ch b+ cn+ (60) and ch+ b cn+ (111) are the double crossovers. Comparing these to the parental types (ch+ b+ cn+ at 780 and ch b cn at 769), we see that cn+ stays with ch+ (parental) and with ch (double crossover), meaning cn is in the middle. The gene order is ch-cn-b.

Multiple choice

Mitochondrial Eve is the woman from whom all living humans are descended matrilineally, and __________________ is the man from whom all living humans are descended patrilineally.

  1. Mitochondrial Adam

  2. Nucleic Adam

  3. X-chromosomal Adam

  4. Y-chromosomal Adam

  5. Somaclonal Adam
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In human genetics, Y-chromosomal Adam (Y-MRCA) is a hypothetical name given to the most recent common ancestor (MRCA) from whom all currently living people are descended patrilineally.