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In beetles, the gene for color and the gene for pattern are located on the same chromosome and exhibit recombination. The lined pattern allele (l) is recessive to the solid unpatterned allele (L), and the aqua color allele (b) is recessive to the blue color allele (B). Geneticists cross a homozygous lined aqua beetle with a homozygous solid blue beetle. Then, they carry out a testcross using the F1 progeny. The parental chromosomes for the testcross are given. Identify all possible gametic haplotypes each parent can form

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Explanation:

The genes that determine color and pattern are linked.

  • Solid pattern allele (L) is dominant over lined pattern (l)
  • Blue color allele (B) is dominant over aqua color (b)

Initial cross

Homozygous lined aqua beetle has the genotype lb/lb

It can produce only 1 type of gamete: lb

X

Homozygous solid blue beetle has the genotype LB/LB

It can produce only 1 type of gamete: LB

The F1 is formed by the union of the parents' gametes, so it will have the genotype  lb/LB

F1 test cross

Test crosses involve a homozygous recessive individual.

The homozygous recessive individual lb/lb can only produce 1 type of gamete:

  • lb

The F1 individual lb/LB  can produce 4 types of gametes:

  • lb - parental
  • LB - parental
  • lB - recombinant
  • Lb - recombinant

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