Genetics Day 3

Today, we learned of different types of genetics, such as: Incomplete Dominance, Sex-Linked Crosses, and Medical Disease Inheritance.

Incomplete Dominance:

Incomplete Dominance is when one allele is not completely dominant over another allele. Here is an example: Yellow fur in guinea pigs is represented by: C^Y C^Y, White is represented by C^W C^W, and Cream is represented by C^Y C^W. Say a white guinea pig crosses with a white guinea pig, and produces all white guinea pigs. Cross a cream guinea pig with a cream guinea pig. Determine the phenotypic ratios.

Here's how you do it:

Simply use the foil method.

So then, you just convert the genotypes to phenotypes.

1 yellow : 2 cream : 1 white.

Sex-Linked crosses

Sex linked crosses are crosses that pass down traits through a sex chromosome.

Here is an example of a problem: 

Red  eyes is dominant over white eyes.

Red = R

White = r

Cross a homozygous red-eyed woman with a white eyed male.

Females are XX and Males are XY. Thus, because males don't have 2 X's, they can only have 1 half of an allele. Here is how you solve this problem:

So then you end up with 2 red-eyed females and 2 red-eyed males.

Medical Disease Inheritance

This has or so with blood types.

O, written as i, always is recessive.

A is written as I^A, AB is written as I^A I^B, and B  is written as I^B.

Blood type A can either be I^A or I^A i.

Blood type AB is the same as above.

Blood type B can either be I^B or I^B i.

Blood type O is I^O I^O or ii.

So here's a sample problem:

A mother has a blood type A, her daughter has blood type AB, and her son, blood type O.

What is the mother's blood?

Answer: I^A i, because without the i, then the son would never be able to have the blood type O.

That's it for this class.