Punnett squares are convenient ways to represent the types and frequencies of gametes and progeny in experimental crosses. This
Punnett square shows the results of a Yy x Yy cross to form F2 progeny. Use your understanding of Mendel’s law of segregation and the rules of probability to complete the Punnett square for this cross.
If the two genotypes are crossed, during meiosis, the alleles segregate and at the point of fertilization randomly unite to form zygote of offspring. Maternal alleles randomly unite with paternal alleles.
Yy x Yy = YY, Yy, Yy and yy.
The Punnet square for the cross is shown in the attached image.
G always pairs with C...So, if there is 30% G, then there's 30% C...which is 60%...that leaves 40% A+T - and you have to split this up too - so 20% Thymine (T) and 20% Adenine (A).