Researchers have a heterozygous fruit fly that exhibits a curly wing phenotype. When they cross that...

Researchers have a heterozygous fruit fly that exhibits a curly wing phenotype. When they cross that fly with a homozygote that has normal wings, they find a 1:1 segregation ratio, which is consistent with simple dominance at the locus that determines wing morphology. However, when they cross two heterozygotes (i.e., a monohybrid cross), they consistently find a 2:1 segregation ratio (2 curly : 1 normal) in the mature flies in the next generation. What is the most likely explanation for the observed deviation from the expected 3:1 segregation ratio? What are the different genotypes produced by the monohybrid cross and what phenotype is associated with each genotype? [Hint: The researchers also notice that the monohybrid crosses produce a smaller number of surviving offspring than normal.]

Expert Solution

If we assume Genotype of homozygote fly with normal wings is CC,then genotype of fly with curly wings will be Cc.

In first cross between homozygote fly with normal wings and curly winged fly

Normal winged fly. Curly winged fly Genotypes CC Cc

Gametes Only one type here two gametes here

That is C. That are C and c

Cross

Gametes	C	c
C	CC(Normal)	Cc(Curly)

So genotypes produced from this cross are CC and Cc that are normal winged fly and curly winged fly in the ratio of 1:1.

In second cross both are heterozygous with curly wings (Cc) and both produces two type of gametes C and c.

)Gametes	C	c
C	CC (Normal)	Cc(curly)
c	Cc(curly)	cc(lethal)

Here ratio is changed from 3:1 to 2(curly):1(normal).

It is due to recessive lethal gene.Lethal gene are the genes which causes death of individual carrying them in recessive or dominant form.lethal genes results from mutation in normal genes essential for normal growth and function.

gladiator answered 2 years ago

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