Concept explainers
To determine:
The percentage of offspring that would be homozygous for the given traits.
Introduction:
A cross that involves hybrids for two traits is called a dihybrid cross. Punnett developed a method to predict the possible offspring of a cross between two known genotypes. It is easier to keep a track of the possible genotypes involved in a cross.
Answer to Problem 12STP
Percentage of offspring homozygous (dominant) for both traits is 1 out of 16= 6.25%.
Percentage of offspring homozygous (recessive) for both traits is 1 out of 16= 6.25%.
This can be checked by drawing a Punnett square for the dihybrid cross.
Explanation of Solution
An organism with genotype ( RrYy) will produce four types of gametes- male and female- each with either the R allele or r allele and either Y or y allele. If a dihybrid cross between two organisms with genotype ( RrYy) is performed, the possible combinations of possible alleles from each parent as shown by Punnett square are:
RRYY, RRYy, RrYy, rryy, RrYY, rrYY, Rryy, rrYy and RRyy .
This can be checked by drawing a Punnett square as shown below.
RY | Ry | rY | ry | |
RY | RRYY | RRYy | RrYY | RrYy |
Ry | RRYy | RRyy | RrYy | Rryy |
rY | RrYY | RrYy | rrYY | rrYy |
ry | RrYy | Rryy | rrYy | rryy |
Out of these the offspring with homozygous genotypes are RRYY (dominant) and rryy (recessive ).
Percentage of offspring homozygous (dominant) for both traits is 1 out of 16= 6.25%.
Percentage of offspring homozygous (recessive) for both traits is 1 out of 16= 6.25%.
Chapter 12 Solutions
Biology Illinois Edition (Glencoe Science)
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