Biology

Genetics and Plant Breeding

1,240 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

The fact that fraternal twins are more similar in intelligence than ordinary siblings suggests the importance of

  1. common hereditary factors

  2. common environmental factors

  3. genetic effects

  4. effects of intrauterine environment
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Fraternal twins share the same genetic relatedness (50%) as ordinary siblings, yet they show greater similarity in intelligence. This indicates that factors beyond genetics contribute to intelligence - specifically, the shared environment they experience both in the womb and growing up together. Common environmental factors like prenatal conditions, family upbringing, and similar life experiences play a crucial role.

Multiple choice

The best summary statement regarding the role of heredity on human intelligence is that

  1. heredity may impose upper limits on intelligence

  2. heredity may impose lower limits on intelligence

  3. intelligence is almost completely related to genetic inheritance

  4. the similarity in IQ scores among maternal relatives is greater than that among paternal relatives
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Heredity sets potential upper bounds on intelligence, but environment determines where within those bounds an individual falls. This reflects the nature-nurture interaction. Neither heredity nor environment alone determines intelligence - it's their interplay.

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.