In: Biology
Please explain!
1) A monohybrid cross for is performed between a Normal eyed Wild type (AA) and true breeding eyeless flies (aa).
Parental cross : AA (Wild Type) x aa (Eyeless)
Gametes: A A a a
F1 Progeny
Male/Female | A | A |
a | Aa | Aa |
a | Aa | Aa |
Genotype: All are heterozygotes
Phenotype: All all Normal Eyed
2) In a cross between two F1 generations.
F2 cross : F1 x F1
Gametes: A a A a
F2 progeny:
Male/Female | A | a |
A | AA | Aa |
a | Aa | aa |
Genotype: 1AA : 2Aa : 1aa
Phenotype: 3 Normal eyed : 1 eyeless
3) The Following conclusion can be made from the question
S_ - Sharp Spines
ss - Dull spines
N_ - Spines
nn- No spines
The Phenomenon observed here is know and Recessive epistasis (9:3:4). Recessive epistasis occurs when the recessive allele at one loci or gene masks or modifies the effect alleles at other loci or gene. Here the function of the gene products of both the alleles occur in series, that is a precursor molecule X is converted to an intermediate precursor A by S_ genotype and this intermediate A precursor is converted to final phenotype by N_ genotype.
4) The recessive allele ss is epistatic over the expression of N allele.