Question

6. In Cross 1, a yellow eyed, long wing fruit fly from a pure breeding strain is mated to a red eye, short wing fruit fly from a pure breeding strain. All of their offspring (F1) had red eyes and long wings. In Cross 2, one of the F1 offspring is mated to a fly with yellow eyes and short wings, and this cross gave the following F2 population: 194 flies with long wings and red eyes, 796 flies with yellow eyes and long wings, 206 flies with yellow eyes and short wings, and 804 flies with red eyes and short wings. a. Assign gene names and allele names and abbreviations for each b. Write the genotypes of the two parents in Cross 1 c. Write the genotype of the F1 offspring and the fly that it mates to (Cross 2) d. Which allele of each gene is dominant and which is recessive? e. What gamete genotypes would you expect from the red/long parent in Cross 2 if the genes involved were assorting independently (i.e. as if they were on different chromosomes)? f. What ratio would you expect to find in the progeny of Cross 2 if the genes involved were assorting independently? Draw a Punnett square to support your answer.

Answer 1

Answer 6:

Given that upon crossing a pure breeding (homozygous) yellow eyed fly with long wings to a red eyed fly with short wings (homozygous state) produced F1 in which all have red eyes and long wings. Hence, red eyes and long wings are dominant traits.

(a)

Gene name	Dominant allele	Recessive allele
Eye color	R (red)	r (yellow)
Wing length	S (long)	s (short)

(b) Genotypes of parents for Cross 1:

Genotype of pure preeding yellow eyed, long winged parent	rrSS
Genotype of pure breeding red eyed, short winged parent	RRss

(c) Genotype of F1 and it's mate:

Genotype of F1	RrSs
Genotype of mate of F1	rrss

(d)

For eye color, allele for red eye is dominant over allele for yellow colored eye.

Also, for wing length, allele for long wings is dominant over short wings.

(e) Gametes formed by red/long parent in Cross 2:

Red/long parent in Cross 2: RrSs. It will form the following four types of gametes:

• RS.
• Rs.
• rS.
• rs.

(f) Ratio for Cross two can be determined using punett square , as follows:

	RS	Rs	rS	rs
rs	RrSs	Rrss	rrSs	rrss

Expected ratio will be 1:1:1:1