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

Sex-influenced genes are coded by

  1. autosomal genes

  2. X linked genes

  3. Y linked genes

  4. epistatic genes

  5. none of the above
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Sex-influenced traits are autosomal traits that are influenced by sex.

Multiple choice

A study of a disorder reveals that monozygotic twins are concordant 40% of the time, whereas full siblings are concordant 10% of the time. Which of the following is the best interpretation of this finding?

  1. The trait has no genetic component.

  2. The trait is completely determined by genetics.

  3. Genes contribute to the trait, but are not deterministic.

  4. The trait must be due to the biology of twinning.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

There is an increased twin concordance, suggestive of a genetic contribution, but since twins are not fully concordant, other non-genetic factors must also be involved.

Multiple choice

Which of the following best explains the threshold model?

  1. A quantitative multifactorial trait

  2. A polygenic multifactorial trait

  3. A multifactorial trait results in a non-disease phenotype such as height

  4. A multifactorial trait exhibits all or none phenotype.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The threshold model postulates that the phenotype is absent until a threshold of liability is reached, after which the phenotype is expressed.

Multiple choice

A balanced polymorphism occurs when

  1. there is selection against the homozygous recessive individuals

  2. there is selection against heterozygotes

  3. there is selection against all genotypes

  4. there is selection against all homozygotes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

A balanced polymorphism occurs when homozygotes are selected relative to heterozygotes.

Multiple choice

Consider a family where both father and son have retinoblastoma. DNA analysis from the child's tumor shows only a single allele from the Rb locus on chromosome 13. Both parents are heterozygous in blood, as is the child. Which allele would you expect is preserved in the tumor?

  1. Mother's

  2. Father's

  3. There is a 50:50 chance that it is the mother's or father's allele.

  4. Both alleles would be abnormal due to genetic rearrangement.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The father's allele would be preserved in the tumor. This is a mutant allele, based on the fact that the father has retinoblastoma.

Multiple choice

Incompletely penetrant genes are expressed in

  1. phenotypes

  2. genotypes

  3. heterozygous individuals

  4. homozygous individuals
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The example of an incompletely penetrant genetic inheritance is multiple sclerosis. It apparently develops when an individual who carries the gene or genes for this disease is attacked by a virus that causes a flu-like illness.

Multiple choice

Which among the following does not characterise polygenic traits?

  1. These are controlled by more than a single pair of alleles.

  2. These are responsible for a number of traits in the phenotype.

  3. These are found in either men or women, but not in both.

  4. The phenotype of an individual depends on alleles in multiple genes.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Polygenic traits are determined by multiple pairs of alleles. Simple Mendelian rules of dominance do not readily apply. Human stature is an example. It results from all of the genes that determine the size of all body parts from head to foot.

Multiple choice

If a single pair of alleles determines the number of fingers for an animal species and homozygous dominant individuals have 8 fingers, heterozygous ones have 7, and homozygous recessive ones have 6, the inheritance pattern would be referred to as

  1. genome imprinting

  2. intermediate expression

  3. pleiotropy

  4. reduced penetrance
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

This hypothetical example would be an example of the intermediate expression of a trait. Apparently, this is rare. For most genes, it is expected that individuals with heterozygous genotypes will have phenotypes like homozygous dominant individuals.

Multiple choice

Few individuals are AB blood types of the ABO blood system. They posses all the features of both type A and type B blood but they are not a blend of them. This is due to the

  1. codominance

  2. dominance

  3. blending

  4. pleiotropy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Codominant traits are the ones in which both alleles are expressed when the phenotype is heterozygous. In the case of the ABO blood type system, A and B are codominant. They are also completely dominant over O.

Multiple choice

The genes for a trait are inherited by son & daughter of a couple but only show up in the phenotype of daughter, they are referred to as

  1. sex-controlled genes

  2. codominant genes

  3. sex-limited genes

  4. sex-linked genes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Only one gender actually has sex-limited genes expressed in the phenotype, while both inherit them. The typical heavy male facial beard is an example of a trait whose inheritance follows this pattern.

Multiple choice

The monozygotic twins may not have identical phenotypes because

  1. their genotypes are different

  2. their phenotypes are effected by environment

  3. their phenotypes are independent of their genotypes

  4. they develop from different zygotes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

While monozygotic twins are identical in genetic makeup, but the individuals after conception and birth can alter their phenotypes.

Multiple choice

The interaction between different genes is termed as

  1. multiple-allelism

  2. mutation

  3. syndrome

  4. epistasis
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

It is described as the interaction between genes. It can be contrasted with dominance, which is an interaction between alleles at the same gene locus.

Multiple choice

Which of the following can be regarded as an exception to Mendel's concept that genes are passed on, unchanged, from one generation to other?

  1. Codominance

  2. Multiple-alleles

  3. Stuttering alleles

  4. Incomplete dominance
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Stuttering or unstable alleles structurally change from generation to generation. Segments of these rare genes are doubled with each generation, resulting in an intensification of a trait. One form of muscular dystrophy apparently can follow this pattern.