Dominant and Recessive and Punnett Squares?

Question

I don't know these answers. I am so confused. We are supposed to make a Punnett Square and answer the question

A disease, (call it whatever), is inherited as an X-linked dominant trait. What will happen if you cross a homozygous recessive woman and a man with hypophosatemia?

Find the genotypes and phenotypes of their sons and daughters.

AND

In a certain kind of flower, the allele for red flowers is co-dominant to the allele for white flowers. A red-flower plant and white-flowered cross. What color with the new plants be when crossed? What is the expected frequency of each color in the first & second generation?

Answer 1

Disease

Let's call the disease trait A and the non-disease trait b.*

If a trait is X-linked, then that means it only shows up in X chromosomes. Women have two, men have one. Since the woman is pure (homozygous) recessive, she has two b traits:

bX and bX

The man, has one A trait, and since the other s*x chromosome is a Y chromosome, it carries no trait for that disease.

AX and Y

So, you place the parents (one on the top, the other on the left). A punnet square is basically algebra, just multiply the variables together (except they're not variables)

_ _ AX___|  Y

bX| AbXX |  bXY   |

bX| AbXX |  bXY   |

--------------------------

And there's ur punnet square, two X's means it's a girl, and an x and a y is a boy!

Genotype - The gene make-up (AbXX / bXY)

Phenotype - What is expressed (Has diease/ Doesn't have disease)

The genotype of any son is bXY, and their phenotype is they don't have the disease.

The genotype of any daughter is AbXX, and their phenotype is they do have the disease.

Codominance

When two codominant alleles are expressed, they mix. So, red plus white equals pink!

Let's say R= red and W = White

The first generation of plants

_ _R__|R

W|RW_|RW|

W|RW_|RW|

They're all pink!

Second generation

_ _R__|W

R | RR_|RW|

W|RW_|WW|

Now, in the second generation the expected frequency is:

25% Red, 50% Pink, and 25% White.

Hope this helps!

*In case you don't know, Capital letters are assigned to the dominant trait and lower case letters to the recessive trait