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GrogVix [38]
3 years ago
5

What phenotypic ratio would you expect as a result of a test cross between two individuals where 9) one that is homozygous reces

sive for alleles at two independent loci?

Biology
1 answer:
olasank [31]3 years ago
8 0

What phenotypic ratio would you expect as a result of a test cross between a dihybrid organism and one that is homozygous recessive for alleles at two independent loci?

a. 3:1

b. 9:3:3:1

c. 1:1:1:1

d. 1:2:1

e. 9:4:2:1

Answer:

c. 1:1:1:1

Explanation:

When a heterozygous individual for two genes is test crossed with a double homozygous recessive individual, the progeny is obtained in 1:1:1:1 phenotypic ratio. This occurs as the heterozygous dominant individual forms four types of gametes in 1:1:1:1 ratio while the homozygous recessive individual would form only one type of gamete having one recessive allele for each gene.  

For example, a test cross between TtRr (tall and red) and ttrr (short and white) would produce a progeny in following ratio=

1 tall, red: 1 tall, white: 1 short, red: 1 short, white

Here, T= tall, t= short, R= red, r= white

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 <span>I is dominant, i is recessive. The A's and B's are just show which allele I is. When there is just one dominant allele, it masks the recessive in blood typing. Remember IA and IB are codominant. 

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_______IA ____ i 

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Sorry, that was difficult on here, hope it's understandable. 
The father's alleles run across the top, the mother's are on the side, you follow to where they meet to find the possibilities for the children. IBIA (AB blood type), IBi (B), IAi (A), and ii (O) are the possibilities in this case. 

Hope that helps!</span>
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