Test: Heredity And Variation 5 - From Past 28 Years Questions

A child will be albino only if it is homozygous for albinism genes (since albinism is a recessive character). As parents have normal skin, it means they are hetrozygous. As a result of cross between two heterozygous parents, 25% of the children will be homozygous recessive. The nature of the second child is not affected in any way by the nature of the first child because both are independent events. 

Crossing over involves physical exchange of genetic material between non sister chromatids of homologous chromosomes, which leads to recombination.

Three types of genome, occur in a typical green plant cell - nuclear genome, mitochondrial genome and chloroplast genome.

If Mendel had studied a plant with 12 chromosomes, he would have encountered linked genes, and hence he would not have arrived at principle of independent assortment

Different types of gametes produced will be   ABC,  AbC,  ABc,  Abc

Molecular weight of chromosome of yeast cell is 2.56 × 10⁹.

Somatic mutation is the mutation occurring in somatic or body cells. Mutations occurring  in germ cells which are transferable to the progeny is called germinal mutation. Mutation occuring in genes is called genetic mutation.

During industrial revolution in England the frequency of melanic forms of species of Peppered Moth (Biston betularia)  increased in polluted areas. Generally the moths are light coloured. This change in colour is known as "Industrial melanism". The change was presumed to be a result of natural selection since the melanic moths better matched the blackened tree trunks where they rest during day.

The mother must have been a haemophilic carrier (X^hX). One of  the twins would have inherited the normal X chromosome and the other would have received the X chromosome carrying the gene for haemophilia.

Normal woman whose father was colour blind would have received  the X will be chromosome from her father  − X^cY →

The number of base pairs (bp) found in one genome of man is 3 × 10⁹.

In human the Y chromosome bears  the androgenic factor or the male determining factor. Whereas in Drosophila the ratio of sex chromosomes to autosomes is the factor determining sex of the individual. 

Downs syndrome develops due to trisomy of the 21^st chromosome. Affected individual possess a characteristic appearance. They have short stature, small round heads, broad forehead, open mouth and projecting lower lip (Mongoloid idiocy).

Hemolytic disease of the newborn occurs when a Rh– mother conceives a Rh+ child.  Mother’s blood starts producing antibodies against the foetal red blood cells.

Round seed shape is dominant over wrinkled. Yellow seed colour is dominant over green seed colour Axial flower position is dominant over terminal.

Independent assortment of genes takes place only when they are located on separate non-homologus chromosomes. Where two or more than two genes are located on same chromosome, independent assortment will not be possible.

According to principle of dominance, out of the two factors of alleles representing different traits of a  character, only one expresses itself.  But when both express themselves it is codominance.

In complementary gene action, both the non allelic pair independently produce similar phenotypes and when present together produce a new phenotype. So, that F₂ ratio 9 : 3 : 3 : 1 would become 9 : 7.

Natural selection operates through differential reproduction. Genetic drift is random change in the allele number and frequency in a gene pool. 

In eukar yotic cells, two cytoplasmic organelles, mitochondria and chloroplast of green plants, contain their own genetic materials.