Question

In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u.. long. The X-linked gene for body color-with two alleles, y ⁺for gray body and y for yellow body-resides at one end of the chromosome at map position 0.0. A nearby locus for eye color, with alleles w ⁺for red eye and w for white eye, is located at map position 1.5. A third X-linked gene, controlling bristle form, with f ⁺ for normal bristles and  f for forked bristles, is located at map position 56.7. Each gene resides on the Xchromosome, and at each locus the wild-type allele is dominant over the mutant allele.

Predict the frequency of gray with white eyes and forked bristles progeny type produced by this mating.

Enter your answer as a percentage to three decimal places (example 0.235 or 0.230).

Frequency=_________

2.

Phenotype	Number
Pale	648
Pale, oval	64
Pale, short	10
Pale, oval, short	102
Oval	6
Oval, short	618
Short	84
Wild type	98
	1630

A wild-type trihybrid soybean plant is crossed to a pure-breeding soybean plant with the recessive phenotypes pale leaf l, oval seed (r), and short height (t). The results of the three-point test cross are shown in the table. Traits not listed are wild type.

Calculate the interference value for these data.

Enter your answer to three decimal places (example 0.201).

Answer 1

2). Interference: 0.263

Explanation:

Phenotype	Number	Genotype
Pale	648	l R T
Pale, oval	64	l r T
Pale, short	10	l R t
Pale, oval, short	102	l r t
Oval	6	L r T
Oval, short	618	L r t
Short	84	L R t
Wild type	98	L R T
	1630

Hint: Always recombinant genotypes are smaller than the non-recombinant genotypes.

Hence, the parental (non-recombinant) genotypes are more in number and their trihybrid genotype is L r t / l R T

1).

If single crossover occurs between L & r..

Normal combination: Lr / l R

After crossover: LR/lr

LR progeny= 84+98 = 182

lr progeny = 64+102 = 166

Total this progeny = 348

The recombination frequency between L&r = (number of recombinants/Total progeny) 100

RF = (348/1630)100 = 21.35%

2).

If single crossover occurs between r & t..

Normal combination: rt / RT

After crossover: rT/Rt

rT progeny= 64+6=70

Rt progeny = 84+10=94

Total this progeny = 164

The recombination frequency between r&t = (number of recombinants/Total progeny) 100

RF = (164/1630)100 = 10.06%

3).

If single crossover occurs between L & t..

Normal combination: Lt / lT

After crossover: LT/lt

LT progeny= 6+98= 104

lt progeny = 10+102=112

Total this progeny = 216

The recombination frequency between L&t = (number of recombinants/Total progeny) 100

RF = (216/1630)100 = 13.25%

Recombination frequency (%) = Distance between the genes (cM)

L----------13.25cM--------T-----------10.06 cM--------------R

Expected double crossover frequency = (RF between h & w) * (RF between w & b)

= 13.25% * 10.06% = 0.0133

The observed double crossover frequency = 10+6 / 1630 = 0.0098

Coefficient of Coincidence (COC) = Observed double crossover frequency / Expected double crossover frequency

= 0.0098 / 0.0133

= 0.737

Interference = 1-COC

= 1-0.737 = 0.263

1). The parental phenotypes or genotypes are not mentioned in the question. It is not possible to answer