In peas,tallness is dominant over dwarfness, and red colour of flowers is dominant over the white colour. When a tall plant bearing red flowers was pollinated with a dwarf plant bearing white flowers, the different phenotypic groups were obtained in the progeny in numbers mentioned against them
$$ \begin{aligned} & \text { Tall, Red }=138 \\ & \text { Tall, } \text { White }=132 \\ & \text { Dwarf, Red }=136 \\ & \text { Dwarf, } \text { White }=128 \end{aligned} $$
Mention the genotypes of the two parents and of the four offspring types.
The result shows that the four types of offspring are in a ratio of $1: 1: 1: 1$. Such a result is observed in a test cross progeny of a dihybrid cross.
The cross can be represented as
Parents Tall and red $(\mathrm{TtRr}) \times$ Dwarf and white (ttrr)
Offsprings
Why is the frequency of red-green colourblindness is many times higher in males than that in the females?
Colourblindness is a X-inked sex inheritance. For becoming colourblind, the female must have the allele for it in both her X-chromosomes and if only one X-chromosome of female possess allele for colour blind character she becomes the carrier for this characteristics But males develop colourblindness when their sole X- chromosome has the allele for it. Thus males are more prone to colour blindness while females are carriers.
If a father and son are both defective in red-green colour vision, is it likely that the son inherited the trait from his father? Comment.
Gene for colourblindness is X-chromosome linked, and sons receive their sole X-chromosome from their mother, not from their father. Male to male inheritances is not possible for X-linked traits in humans.
In the given case the mother of the son must be a carrier (heterozygous) for colour blindness gene, thus transmitting the gene to her son.
Discuss why Drosophila has been used extensively for genetical studies?
Morgan worked with the tiny fruit flies, Drosophila melanogaster, which were found to be suitable for genetical studies due to the following characteristics
(i) They could be grown on simple synthetic medium in the laboratory.
(ii) They complete their life-cycle in about two weeks.
(iii) A single mating could produce a large number of progeny flies.
(iv) A clear differentiation of the sexes- the male and female flies are easily distinguishable.
(v) It has many types of variations (hereditary) that can be seen with low power microscopes.
How do genes and chromosomes share similarity from the point of view of genetical studies?
By 1902, the chromosome movement during meiosis had been worked out.
Walter Sutton and Theodore Boveri, (1902) noted that the behaviour of chromosomes was parallel to the behaviour of genes and used chromosome movement to explain Mendel's Laws.
They studied the behaviour of chromosomes during mitosis (equational division) and during meiosis (reduction division). The chromosomes as well as genes occur in pairs and the two alleles of a gene pair are located of homologous sites of homologous chromosomes.
Chromosome movement in meiosis and germ cell formation in a cell with four chromosomes. Chromosomes segregate when germ cells are formed