How is a punnett square a mode for what happens during meiosis?

Answer 1

As I'm sure you know, we get half of our genetic material from each parent, and we have two genes for every characteristic, one from mother and one from father, with the exception of a few traits found on the end of the X chromosome in males, who have an XY configuration and must depend on whichever gene the mother gave for certain characteristics such as color vision and proper blood clotting.

During meiosis, egg or sperm cells are formed when our chromosomes are split in half to allow for the fertilization process to complete the genetic codes from the other parent.

A Punnett square can be used to predict only which possible gene might be given by a single egg or sperm cell based on genotype of the parent, if known, but it is incomplete without the other portion of the code. However, it can be used to show how one parent may contribute either a dominant or recessive gene for a particular trait if the parent's complete genotype is known.

For example, I know that my blood type is A, which is my phenotype, but that my genotype is AO because my father was type O and that is the only gene a type O person can donate. Type O genes are recessive, so that phenotype would not show up if someone inherits either a type A or type B gene from the other parent, but the type O gene would have a 50-50% chance of ending up in my egg cells after meiosis split my blood type gene combination (AO), called the genotype, in half. Half of my eggs would therefore contain type A genes and the other half would have type O genes, and that could be put on a Punnett square to show the 50-50% chance of my offspring having either type A or type O blood, depending on which gene he inherits from me, but the father's genotype is needed to complete the full Punnett square possiblities.

Since my husband is type O, he could donate only an O gene in every sperm cell, which means that his meiotic Punnett square would have only type O genes in every square.

For a true genetic prediction, both genotypes of each parent must be combined, but at least in meiosis, it can be predicted that I have a 50-50% chance to donate either a type A gene or a type O gene to my offspring, while my husband has a 100% chance to donate a type O gene because his genotype has to be OO. Our son, therefore must be either type A or type O and has a 50% chance of having either. We don't know because his blood type has never been tested, but those are his only possibilities.

Since neither my husband nor I have type B genes, it would be impossible for our child to have type B or AB blood, which could be deduced from a Punnett square for meiosis for his mother and his father since our genotypes for this trait are known positively.

I hope this helped!