Answer:
A punnet square can be described as a diagram which is made to check the outcomes of a cross.
To check the probability of the offsprings of a cross between homozygous dominant thumb shape parent with a homozygous recessive thumb shape parent, let's draw a punnet square:
t t
T Tt Tt
T Tt Tt
The results of the punnet square depict that:
Genotype: All of the offsprings will be heterozygous for the thumb shape trait. Tt will be the genotype.
Phenotype: All of the offsprings will show the thumb shape like the thumb shape of the dominant parent.
Answer:
Because natural selection selects for it. Thus it persists.
Explanation:
You have to understand heterozygote advantage. Basically, it's where heterozygotes have an advantage over homozygotes. In the case of sickle cell disease, heterozygotes have an advantage, and natural selection favors whatever is advantageous. Thus, because heterozygotes each have one recessive sickle-cell allele, as natural selection favors the heterozygotes, the recessive sickle-cell allele persists and remains in the gene pool.
