The Punnett squares provide information about the genotype and phenotype of individuals produced by the crosses. Cross 1) 3/4 = 75%. Cross 2) 2/4 = 50%.
What is a punnett square?
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.
Available data:
- S represents a dominant star-bellied gene
- s represents the recessive trait.
We will assume this is a diallelic gene expressing complete dominance, this is, the dominant allele S completely hides the expression of the recessive allele s.
1st cross: mother and father both have star bellies and the recessive gene
Parentals) Ss x Ss
Gametes) S s S s
Punnett square) S s
S SS Ss
s Ss ss
F1)
Genotype
1/4 = 25% of the progeny is expected to be h0m0zyg0us dominant SS
2/4 = 50% of the progeny is expected to be heter0zyg0us Ss
1/4 = 25% of the progeny is expected to be h0m0zyg0us recessive ss
Phenotype
3/4 =75% of the progeny is expected to have star bellies
1/4 = 25% of the progeny is expected not to have star bellies
The chance their child will have a star-belly is 3/4 or 75%.
2nd cross: motherhas star bellies and the recessive gene and the father does not have a star-belly
Parentals) Ss x ss
Gametes) S s s s
Punnett square) S s
s Ss ss
s Ss ss
F1)
Genotype
2/4 = 50% of the progeny is expected to be heter0zyg0us Ss
2/4 = 50% of the progeny is expected to be h0m0zyg0us recessive ss
Phenotype
2/4 =50% of the progeny is expected to have star bellies
2/4 = 50% of the progeny is expected not to have star bellies
The chance their child will have a star-belly is 2/4 or 50%
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