Question

A geneticist is mapping the chromosomes of the newly captured gremlin. Stripe is heterozygous for three linked genes with alleles Ee, Hh, and Bb, that determine if gremlins are evil (E), have hair (H), and biting teeth (B). In order to determine if the three genes are linked, a standard testcross was done, and the 1000 offspring had the following genotypes: 48 400 ee Hh bb ee hh Bb ee Hh Bb Ee Hh Bb Ee hh bb Ee hh Bb Ee Hh bb ee hh bb 426 38 What is the recombination frequency between genes E and H? 7.4% º 8% O 40% o 92% O 8.4% Submit Previous Answers Request Answer X Incorrect; Try Again; One attempt remaining

Answer 1

Answer:

Recombination frequency between E & H = 8%

Explanation:

Testcross will be done between triple heterozygote and triple recessive parent. Triple recessive parent (eehhbb) will produce only one type of gametes, ehb). If we remove ehb from each of given genotype, we can obtain the triple zygote genotypes. Based on the larger number, we can judge the genotype of triple zygote.

48 eeHhbb = eHb

36 eehhBB = ehB

400 eeHhBb = eHB

4 EeHhBb = EHB

426 Eehhbb = Ehb

46 EehhBB = EhB

38 EeHhbb = EHb

2 eehhbb = ehb

Hint: Non-recombinant (parental) combinations are produced more in number than recombinants. The parental (non-recombinant) genotypes is eHB/Ehb

1).

If single crossover occurs between e&h…

Normal combination: eH/Eh

After crossover: eh/EH

eh progeny=36+2=38

EH progeny = 38+4=42

Total this progeny = 80

Total progeny = 1000

The recombination frequency between e&h = (number of recombinants/Total progeny) 100

RF = (80/1000)100 = 8%

2).

If single crossover occurs between h&b

Normal combination: HB/hb

After crossover: Hb/hB

Hb progeny= 38+48 = 86

hB progeny = 36+46 = 82

Total this progeny =168

The recombination frequency between h&b = (number of recombinants/Total progeny) 100

RF = (168/1000)100 = 16.8%

3).

If single crossover occurs between e&b…

Normal combination: eB/Eb

After crossover: eb/EB

eb progeny=48+2 = 50

EB progeny = 46+4=50

Total this progeny = 100

Total progeny = 1000

The recombination frequency between e&b = (number of recombinants/Total progeny) 100

RF = (100/1000)100 = 10%   

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

h--------8cM------e----10cM----b

The order of genes = h—e---b