In Drosophila melanogaster, a single mating could produce a large number of progeny flies, and they complete their life cycle in about _______ weeks.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Two
• One
• Four
• Six
Correct Option: A  [ Two ]

Remark: Drosophila melanogaster complete their life cycle in about two weeks, and a single mating could produce a large number of progeny flies.

Morgan observed that when two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations were much higher than the non-parental type, which he described as physical association or _______.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Linkage
• Recombination
• Assortment
• Mutation
Correct Option: A  [ Linkage ]

Remark: Morgan coined the term linkage to describe this physical association of genes on a chromosome.

The generation of non-parental gene combinations due to the physical association of genes is described by Morgan using the term _______.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Recombination
• Linkage
• Crossing Over
• Mutation
Correct Option: A  [ Recombination ]

Remark: Morgan coined the term recombination to describe the generation of non-parental gene combinations.

Morgan found that the genes white and yellow in Drosophila were very tightly linked and showed only _______ per cent recombination.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• 1.3
• 37.2
• 50
• 25
Correct Option: A  [ 1.3 ]

Remark: The genes white and yellow were very tightly linked and showed only 1.3 per cent recombination.

Morgan's student Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the _______ between genes.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Distance
• Linkage strength
• Allelic difference
• Dominance level
Correct Option: A  [ Distance ]

Remark: Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes.

Traits such as human height or skin colour, which are controlled by three or more genes, are called _______ traits.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Polygenic
• Monogenic
• Pleiotropic
• Multiple allelic
Correct Option: A  [ Polygenic ]

Remark: Traits generally controlled by three or more genes are called as polygenic traits.

Besides the involvement of multiple genes, _______ inheritance also takes into account the influence of environment.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Polygenic
• Mendelian
• Sex-linked
• Co-dominant
Correct Option: A  [ Polygenic ]

Remark: Besides the involvement of multiple genes, polygenic inheritance also takes into account the influence of environment.

The underlying mechanism of pleiotropy in most cases is the effect of a gene on _______ pathways which contribute towards different phenotypes.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Metabolic
• Hormonal
• Nervous
• Structural
Correct Option: A  [ Metabolic ]

Remark: The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes.

The initial clue about the genetic/chromosomal mechanism of sex determination came from the cytological observations made in a number of _______.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• Insects
• Mammals
• Birds
• Reptiles
Correct Option: A  [ Insects ]

Remark: The initial clue about the genetic/chromosomal mechanism of sex determination can be traced back to some of the experiments carried out in insects.

In 1891, Henking traced a specific nuclear structure during spermatogenesis in a few insects and named it the _______ body, which was later identified as the X-chromosome.

[Principles-of-Inheritance-and-Variation] [class-xii ]

• X
• Y
• Z
• W
Correct Option: A  [ X ]

Remark: Henking (1891) could trace a specific nuclear structure all through spermatogenesis in a few insects, and he gave a name to this structure as the X body.