Who were the three scientists that independently rediscovered Mendel's results in 1900?

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

• Watson, Crick, and Franklin
• Sutton, Boveri, and Morgan
• de Vries, Correns, and von Tschermak
• Beadle, Tatum, and Lederberg
Correct Option: C  [ de Vries, Correns, and von Tschermak ]

Remark: In 1900, three scientists—de Vries, Correns, and von Tschermak—independently rediscovered Mendel’s results on the inheritance of characters.

Who noted that the behaviour of chromosomes was parallel to the behaviour of genes and used it to explain Mendel's laws?

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

• T.H. Morgan
• Gregor Mendel
• Watson and Crick
• Walter Sutton and Theodore Boveri
Correct Option: D  [ Walter Sutton and Theodore Boveri ]

Remark: In 1902, Walter Sutton and Theodore Boveri noted that the behaviour of chromosomes was parallel to the behaviour of genes and used chromosome movement to explain Mendel’s laws.

The synthesis of Mendelian principles with the knowledge of chromosomal segregation is known as:

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

• The Law of Segregation
• The Chromosomal Theory of Inheritance
• The Theory of Evolution
• Molecular Biology
Correct Option: B  [ The Chromosomal Theory of Inheritance ]

Remark: Sutton united the knowledge of chromosomal segregation with Mendelian principles and called it the chromosomal theory of inheritance.

Who provided experimental verification for the Chromosomal Theory of Inheritance?

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

• Gregor Mendel
• Charles Darwin
• Thomas Hunt Morgan
• Watson and Crick
Correct Option: C  [ Thomas Hunt Morgan ]

Remark: Experimental verification of the chromosomal theory of inheritance was provided by Thomas Hunt Morgan and his colleagues through their work with fruit flies, Drosophila melanogaster.

Which organism did T.H. Morgan use for his genetic studies?

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

• Garden pea (Pisum sativum)
• Snapdragon (Antirrhinum sp.)
• Fruit fly (Drosophila melanogaster)
• Neurospora crassa
Correct Option: C  [ Fruit fly (Drosophila melanogaster) ]

Remark: Morgan worked with the tiny fruit flies, Drosophila melanogaster, which were found very suitable for such studies.

Morgan observed that when two genes in a dihybrid cross were on the same chromosome, the proportion of parental gene combinations was:

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

• Much lower than the non-parental type
• Equal to the non-parental type
• Much higher than the non-parental type
• Absent in the F2 generation
Correct Option: C  [ Much higher than the non-parental type ]

Remark: Morgan saw 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. He attributed this to the physical association or linkage of the two genes.

The term coined by Morgan to describe the physical association of genes on a chromosome is:

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

• Recombination
• Linkage
• Assortment
• Segregation
Correct Option: B  [ Linkage ]

Remark: Morgan coined the term linkage to describe this physical association of genes on a chromosome and the term recombination to describe the generation of non-parental gene combinations.

Which student of Morgan used the frequency of recombination between gene pairs to measure the distance between genes and create genetic maps?

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

• Walter Sutton
• Theodore Boveri
• Reginald Punnett
• Alfred Sturtevant
Correct Option: D  [ Alfred Sturtevant ]

Remark: Morgan's student Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and ‘mapped’ their position on the chromosome.

Traits like human height and skin colour, which show a continuous range of variation, are generally controlled by three or more genes. Such traits are called:

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

• Pleiotropic traits
• Monogenic traits
• Polygenic traits
• Co-dominant traits
Correct Option: C  [ Polygenic traits ]

Remark: Traits that are generally controlled by three or more genes are called polygenic traits. They are not distinct in their occurrence and are spread across a gradient, like human height or skin colour.

In polygenic inheritance, the phenotype reflects the contribution of each allele, meaning the effect of each allele is:

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

• Dominant
• Recessive
• Additive
• Subtractive
Correct Option: C  [ Additive ]

Remark: In a polygenic trait, the phenotype reflects the contribution of each allele; i.e., the effect of each allele is additive. The number of each type of allele in the genotype determines the phenotype, such as the darkness or lightness of skin.