Principles of Inheritance and Variation Test - 21

Mendel conducted hybridization experiments for 7 years on Pea plant between 1856 to 1863 and his data was published in 1865

A set of genes at different loci on the same chromosome tend to act as a single pair of genes in meiosis instead of undergoing independent assortment. The chromosome translocation is a chromosome abnormality caused by rearrangement of parts between non homologous chromosomes. Hence in translocation, there is movement of the gene from one linkage group to another and lead to change the position of the gene.

1.   A.Codominant – Alleles of both parents are expressed in the progeny.

2.  Supplementary genes - Two independent pairs of genes, which interact to produce a new trait together, but each dominant gene alone produces its own trait, are called Supplementary genes.

3.  Complementary genes - Two independent pairs of genes, which interact to produce a trait together, but each dominant gene alone does not show its effect, are called complementary genes

4.  Recessive genes – Allele which is unable to express its effect in the heterozygous condition or in the presence of dominant allele is called Recessive allele.

When heterozygous tall (Tt) is crossed with homozygous recessive dwarf (tt), it is said to be test cross. In the 50% progeny are heterozygous tall (Tt) and remaining 50% progeny are homozygous recessive dwarf (tt) are formed.

So, the correct option is ‘50% recessive’.

In family history, father and mother have normal vision, the probability of daughter becoming colour blindness is 0%, because in both parents no presence of genes for colour blindness.

XY is the sex complement of a male child with Down's syndrome. The cause of Down's syndrome is non-disjunction of 21st chromosome during oogenesis.

This chromosomal abnormality is related with autosome so, the sex complement of a male child in this syndrome will be XY.

Phenylketonuda was discovered by the Norwegian physician A Fooling in 1934, an autosomal recessive mutation of gene on chromosome 12. Phenylketonuria results when there is a deficiency of liver enzyme phenylalanine hydroxylase that converts phenylalanine into tyrosine.

Increased phenylalanine in the blood interferes with brain development, muscles and cartilage of the legs may be defective and the patients cannot walk properly.

The complementary genes are two pairs of non allelic dominant genes (i.e., present on separate gene loci), which interact to produce only one phenotypic trait, but neither of them if present alone produces the phenotypic trait in the absence of other.