Need help on making punnet squared for the following question:?

Question

2. In the years after the rediscovery of Mendel’s work at the turn of the 20th century geneticists found exceptions to and extensions of his principles. These include the existence of multiple alleles at a locus, modification of dominance relationships, interactions between different genes controlling the same phenotype, various kinds of epistasis and the existence of lethal alleles. Describe three of these, using punnet square diagrams to illustrate your answers.

Answer 1

Okay, so you have to choose three, I am choosing multiple alleles at a locus, modification of dominance relationships and lethal alleles.

1. Multiple Alleles at a Locus

One of the most common and easiest understood is blood type.  You can have the A allele, B allele or O allele (multiple typically indicates more then 2).  For ease, I will use A, B and O in the punnet square (O is recessive), but they are commonly denoted as an I with the superscript A or B and a little i for O.

This is a punnet square for AO and BO

_ _ A _ O

B _ AB _ BO

O _ AO _ OO

The parents have blood types A and B, but the offspring can have AB, B, A or O.

2. Modification of Dominance Relationships

There are several modifications of dominance relationships, but I will show one for incomplete dominance.  A typical example is with red and white flowers. A red flower is RR and a white flower is WW, because it is incomplete dominance, both traits are dominant.

The punnet square is for RR and WW

_ _ R _ R

W _ RW _  RW

W _ RW _ RW

The parents are red and white, but because both are dominant the offspring are all pink, a mix between the two.

3. Lethal Alleles

One example of lethal alleles is with genetic disorders.  I will use an example for skeletal dysplasia, or dwarfism.  It is a dominant disorder (there are many many different types and they are sure to be inherited differently, but for ease of the example, I will treat it as a dominant disorder), but if it is received in the dominant homozygous form it is lethal.

This is a punnet square for Dd and Dd (two people who both have skeletal dysplasia)

_ _ D _ d

D _ DD _ Dd

d _ Dd _ dd

For this cross, 25% of the offspring will inherit the lethal alleles (DD), 50% will have skeletal dysplasia (Dd) and 25% will be 'normal' (dd)

I hope this is what you were looking for and that it helps!