Question

717 pts). In Drosophila, two recessive mutations delta vein (d) and rough eye (r) both map to chromosome 3 and are known to be 20 m.u. apart. Another recessive mutation, garnet eye color (a) has been mapped to the X chromosome. A delta veined, rough and garnet eyed- female was crossed to a wild-type male. The resulting fī females are testcrossed to delta-veined, rough and, garnet-eyed males. dng larg & ORG/ A. (6pts) Write the genotype of the Fı female and the tester male. DR Goraxdratdira B. (10pts) Write the phenotypes and the proportions of the progeny (F2) of the Fi female testcrossed to the triple recessive; delta vein, rough and garnet-eyed male. (You can write the phenotype by using the one letter symbol of the gene).

Answer 1

In a drosophila A male has 1X chromosome and Female has 2X chromosome

if a mutant is recessive (dd,rr,gg).It means the wild should  be Dominant either homozygous or Heterozygous

But note these genes are transmitted through X and a male has only 1X chromosome.So A wild type  male should have all dominant genes in its only X chromosome otherwise it will be a mutant.So the Genotype of the wild male is DRG

For a female to be mutant it should have all recessive genes and since it has two X chromosome its phenotype will be (ddrrgg)

A cross that involves X chromosome in drosophila will be

X (Male) vs XX (Female)

The cross would be

DRG x ddrrgg

A female from the resulting cross will not express the mutation but will be a carrier .its genotype is DdRrGg .

A male who is mutant for all three genes will have genotype drg

So F1 Female :DdRrGg ,Tester Male: drg

A cross between F1 Female :DdRrGg x Tester Male: drg (Triple recessive)

During a cross the alleles in a female will assort in different combinations.

the number of combination possible can be calculated by the product rule.There are three genes and either a dominant or recessive can be present.   

Two understand this assume three vacant slots for three different genes _ _ _

In each vacant slot either dominant or recesive of one gene is present .This is the same for other two genes son now we calculate the possible number of combination that can happen.Since these genes assort independently at the same time we can use the product rule to calculate 2*2*2=8 combination.

In order to get 8 combination we can use punnett square in asequential manner

	R	r
D	DR	Dr
d	dR	dr

	G	g
DR	DRG	DRg
Dr	DrG	Drg
dR	dRG	dRg
dr	drG	drg

cross between F1 Female :DdRrGg x Tester Male: drg (Triple recessive)

The phenotypes are indicated by the dominant gene only or the recessive

	drg	Phenotype
DRG	DdRrGg	DRG
DrG	DdrrGg	DrG
dRG	ddRrGg	dRG
drG	ddrrGg	drG
DRg	DdRrgg	DRg
Drg	Ddrrgg	Drg
dRg	ddRrgg	dRg
drg	ddrrgg	drg

Total no of Phenotypes possible 8

The proportion of the phenotypes in the above cross (1:1;1:1:1:1:1:1)