Question

1. List the possible genotypes of the parents if a cross resulted in a F1-generation consisting of 50% white colonies and 50% red colonies:
2. List the possible genotypes of the parents if the cross resulted in a F1-generation consisting of 100% tryptophan independent colonies:

c. Give the genotypes and their percentages resulting from a cross between a homozygous independent tryptophan parent and a heterozygous tryptophan independent parent:

1. Following a RrTt x RrTt cross, state the fraction of the offspring predicted to have a genotype that is heterozygous for both characteristics and the fraction that would be homozygous for both characteristics .
2. What is a dominant trait versus a recessive one?

Answer 1

a. 50% Red and 50% white colonies is result of test cross.In test cross, heterozygous dominant is crossed with the pure precessive pure breed.

The red color is dominant and determined by the allele-'R' while the recessive white color is determined by 'r'

A heterozygous dominant Rr if crossed with homozygous recessive rr

The resultant progenies are-see the image below.

Therefore for 50% red and 50% white offsprings, the parental genotypes are

Rr and rr.

b. The tryptophane independency is determined by a dominent allele 'T" and trytophane dependency is determined by recessive allele 't'

If a purebreed (homozugous) dominant parent 'TT' is crossed with the homozygous recessive parent 'tt'-

then the F1 offspring will be 100% tryptophane independent.

c. if a  homozygous independent tryptophan parent (TT) and a heterozygous tryptophan independent parent (Tt) crossed

the result would be-

50% homozygous independent tryptophan (TT)

50% heterozygous tryptophan independent (Tt).

See the figure below.

a. Following a RrTt x RrTt cross-

the fraction of the offsprings having genotype

Heterozygous for both characteristic (RrTt)- 1/4 or 25% (red tick in the following figure)

Homozygous for both characteristic -RRTT, RRtt, rrTT and rrtt ----1/4 or 25% (red dot in the figure).

b. A dominant is one varient of gene which can mask the characters of other varient when both of the varient is present. The varient which is masked by the dominant one is called recessive.

If two pure breed contrasting characters are crossed, then the dominant will be one, which expressd in the F1 progeny-

for example- the red flower RR) and the white flower (rr) is crossed. the genotype of the progeny will be Rr.

In the offspring (Rr), The dominant character will expressed and the recessive character will be masked.