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)
717 pts). In Drosophila, two recessive mutations delta vein (d) and rough eye (r) both map...
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