1. Imagine hypothetically that the gender of a reptile is controlled by a single
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Question
1. Imagine hypothetically that the gender of a reptile is controlled by a single gene with two alleles, designated A and a. The outcome of this trait is affected by the temperature of the environment. When raised in a cooler environment, the dominant A allele confers maleness, and the a allele confers femaleness. However, when raised in a warmer environment, the homozygote aa animal is male. If a heterozygous individual is crossed to a female reptile, what are the proportions of offspring that are male and female when raised in a cool environment? How do the proportions change if the offspring are raised in a warm environment?
2. In the laboratory, a genetics student crossed flies with normal long wings to flies with mutant short wings, which the student believed to be a recessive trait. In the F1 generation, all flies had long wings. In the F2 generation, the following results were obtained:
792 long-winged flies and 208 short-winged flies
Is this gene behaving according to standard Mendelian genetics? What do the data suggest about the short-winged mutation?
Explanation / Answer
1)
In cooler temperature AA confers to male and aa to female.
Then AA x aa = Aa; Aa
The resultant offspring are males.
In warm temperature aa confers to male and Aa to female.
Then, aa x Aa; the resultant offspring are a male and a female.
2)
When the normal long winged fly crossed with short winged mutant fly, the resultant offspring produced are 792 long winged and 208 short mutant flies. According Mendelian monohybrid cross ration the resultant progeny should be 3:1 ratio (standard)
But, here the long winged = 1000/792 = 1.26
Short mutants = 1000/208 = 4.8.
The progeny produced slightly deviated from the monohybrid cross ratio and not perfectly fit into standard Mendelian genetics.
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