A) if a large number of matings were made between two double heterozygotes, what
ID: 187605 • Letter: A
Question
A) if a large number of matings were made between two double heterozygotes, what phenotypic ratio would be expected in the progeny? B) this phenotypic ratio is a result of what mode of inheritance? C) what phenotypic ratio would be expected is rabbits homozygous recessive for trait A and heterozygous for trait B were mated to rabbits heterozygous for both traits?In rabbits, one enzyme (the product of a functional gene A) is needed to produce a substance needed for hearing. Another enzyme (the produce of a functional gene B) is needed to produce another substance also required for normal hearing. The genes responsible for the two enzymes demonstrate independent assortment. Individuals homozygous for either one or both of the nonfunctional recessive alleles, a or b, are deaf. 6) If a large number of matings were made between two double heterozygotes, what phenotypic ratio would be expected in the progeny? This phenotypic ratio is a result of what mode of inheritance? What phenotypic ratio would be expected if rabbits homozygous recessive for trait A and heterozygous for trait B were mated to rabbits heterozygous for both traits? a) b) c)
Explanation / Answer
a)given that,
only A-B is normal and
aaB, A-bb, aabb are deaf.
The cross is between AaBb x AaBb (4x4 Punnett square), the result comes: normal (A-B) is 9 and 7 deaf in which 3 are A-bb + 3 are aaB- and 1 aabb, 4 kinds of gametes are produced and the phenotypic ratio of F1 generation is 9:3:3:1.
b) This phenotypic ratio is a result of epistasis i.e.double recessive epistasis.
c) The cross between aaBb x AaBb, where aaBb produces gametes aB, ab and AaBb produces gamete AB, Ab, aB and ab (2x4 Punnett square).
| AB | Ab | aB | ab |
aB | AaBB | AaBb | aaBB | aaBb|
ab | AaBb | Aabb | aaBb | aabb |
expected phenotypic ratio would be 3 : 5 ( 3 are normal and 5 are deaf).
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