By 1902, the movement of structures called _______ during meiosis had been worked out, which Walter Sutton and Theodore Boveri noted was parallel to the behaviour of genes.

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

• Chromosomes
• Factors
• Nucleoli
• Centrioles
Correct Option: A  [ Chromosomes ]

Remark: By 1902, the chromosome movement during meiosis had been worked out, which led Sutton and Boveri to note that the behaviour of chromosomes was parallel to the behaviour of genes.

Thomas Hunt Morgan worked with Drosophila melanogaster because it could be grown on simple medium and completed its life cycle in about _______ weeks.

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

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

Remark: Drosophila melanogaster complete their life cycle in about two weeks.

Morgan coined the term _______ to describe the physical association of genes on a chromosome, noting that parental gene combinations were much higher than non-parental types.

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

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

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

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

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

• 1.3
• 37.2
• 50.0
• 25.0
Correct Option: A  [ 1.3 ]

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

Traits generally controlled by three or more genes, such as human height or skin colour, 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, as seen in human skin colour.

[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 single 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.

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

Thomas Hunt Morgan worked with the tiny fruit fly, Drosophila melanogaster, to provide experimental verification of the chromosomal theory of inheritance.

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

• Drosophila melanogaster
• Pisum sativum
• Musca domestica
• Antirrhinum sp.
Correct Option: A  [ Drosophila melanogaster ]

Remark: Thomas Hunt Morgan worked with the tiny fruit flies, Drosophila melanogaster, which were found very suitable for studies related to the chromosomal theory of inheritance.

Drosophila melanogaster complete their life cycle in about _______ weeks, making them suitable for genetic studies.

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

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

Remark: Drosophila melanogaster complete their life cycle in about two weeks.