END OF LECTURE QUESTIONS Coracle bugs spin around on the surface of small stream
ID: 133536 • Letter: E
Question
END OF LECTURE QUESTIONS Coracle bugs spin around on the surface of small streams. One true-breeding strain of bugs spins only to the right and a different true-breeding strain spins only to the left. When the two strains are crossed, the F1 progeny go straight ahead. Crossing of the F1 progeny results in F2 progeny that are 9/16 straight 4/16 left and 3/16 right. A) How many genes are involved in development of this trait? B) Define symbols for the gene(s) and give the genotype for each phenotype of bugs in the P, F1, and F2 generations outlined above. You can use an underscore to represent multiple genotypes if applicable - ex. A AA or Aa You are studying a gene that controls ossicone (horn) length in giraffes. The wild-type long-ossicone allele (L) is dominant to the mutant short-ossicone () allele.. However the L allele is only 60% penetrant. You cross two giraffes, one heterozygous (LI) and one homozygous recessive (II). What phenotypic progeny classes do you expect and at what frequencies (assume the penetrance of L applies equally to both homozygotes and heterozygotes).Explanation / Answer
Answer:
1).
Recessive epistasis (9:3:4)
A Punnet Square for the AaBb x AaBb cross is shown below. Rather than the 9:3:3:1 seqregation of phenotypes normally seen with an AaBb x AaBb dihybrid cross, the phenotypic ratio is 9:3:4. There are only three different phenotypes for straight, right and left. The individual with genotype recessive for both traits, i.e. aabb, has the same albino phenotype as the aaBB and aaBb individuals due to epistasis. The left phenotype masks any phenotype that might be caused by the recessive homozygous, recessive bb genotype.
A_B_ = straight
A_bb = right
aaB_ or aabb = left
AAbb (right) x aaBB(left)------Parents
AaBb (straight)-------------------F1
AaBb x AaBb ------------------Selfcross
AB
Ab
aB
ab
AB
AABB (straight)
AABb(straight)
AaBB(straight)
AaBb(straight)
Ab
AABb (straight)
AAbb (right)
AaBb(straight)
Aabb (right)
aB
AaBB (straight)
AaBb(straight)
aaBB (left)
aaBb (left)
ab
AaBb(straight)
Aabb (right)
aaBb (left)
aabb (left)
AB
Ab
aB
ab
AB
AABB (straight)
AABb(straight)
AaBB(straight)
AaBb(straight)
Ab
AABb (straight)
AAbb (right)
AaBb(straight)
Aabb (right)
aB
AaBB (straight)
AaBb(straight)
aaBB (left)
aaBb (left)
ab
AaBb(straight)
Aabb (right)
aaBb (left)
aabb (left)
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