Punnett squares are used to get the genotypic and phenotypic frequencies among the progeny produced from a cross. Punnett squares and answers below.
<h3>What is a punnett square?</h3>
The Punnett square is a graphic representation that shows the different types of gamete combinations according to the alleles involved in a cross.
Punnett square shows the probabilities of getting offspring with different genotypes and their consequent phenotypes.
In the exposed example,
- Diallelic genes that codes for color
- Y = yellow ⇒ dominant allele
- y = blue ⇒ recessive allele
We will assume complete dominance, meaning that with at least one dominant allele in the genotype, the expressed color is yellow.
1)
a- Cross 1
Parentals) YY x Yy
Gametes) Y Y Y y
Punnett square) Y Y
Y YY YY
y Yy Yy
F1) Genotype
1/2 = 50% of the progeny is expected to be h0m0zyg0us dominant, YY
1/2 = 50% of the progeny is expected to be heter0zyg0us, Yy
Phenotype
100% of the progeny is expected to be yellow.
b- Cross 2
Parentals) YY x yy
Gametes) Y Y y y
Punnett square) Y Y
y Yy Yy
y Yy Yy
F1) Genotype
100% of the progeny is expected to be heter0zyg0us, Yy
Phenotype
100% of the progeny is expected to be yellow.
2)
a. What are the resulting phenotypes? Only yellow kernels
b. Are there any blue kernels? No
c. How can you tell whether or not there are blue kernels?
Blue is the recessive phenotype for kernels. Assuming complete dominance, since all genotypes are expected to carry at least one dominant allele, all the F1 kernels are yellow.
3) Let us cross two heter0zyg0us individuals from the F1
Parentals) Yy x Yy
Gametes) Y y Y y
Punnett square) Y y
Y YY Yy
y Yy yy
F1) Genotype
1/4 = 25% of the progeny is expected to be h0m0zyg0us dominant, YY
1/2 = 50% of the progeny is expected to be heter0zyg0us, Yy
1/4 = 25% of the progeny is expected to be h0m0zyg0us recessive, yy
Phenotype
75% of the progeny is expected to be yellow.
25% of the progeny is expected to be blue.
4)
a. What are the genotypes of the F2 generation?
- 25% YY (h0m0zyg0us dominant)
- 50% Yy (Heter0zyg0us)
- 25% yy (H0m0zyg0us recessive)
b. What are their phenotypes?
- 75% yellow kernels
- 25% blue kernels
c. Are there more or fewer blue kernels than in the F1 generation?
More. Blue kernels appeared in the F2.
5. Assuming independent genes, the , are as follows
<u>Gametes</u>
a. YY Ss ⇒ YS, YS, Ys, Ys
b. Yy Ss ⇒ YS, Ys, yS, ys
You can learn more about punnett squares at
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