1. Homozygous & Heterozygous
Homo-means the same as
Homozygous--a genotype that has two identical alleles.
Homozygous dominant-AA
Homozygous recessive-- aa

2. Homozygous & Heterozygous
Hetero—means difference between two
Heterozygous—a gene has two different alleles(one dominant allele & one recessive allele).
Aa Tt

3. Punnett Squares

4. Turn to your shoulder partner to think about this question.
Is there anyway to predict what the distribution of traits will be in the F₃ generation?
Turn to your shoulder partner to think about this question.

5. Let’s see if we can figure out if any of the larkeys will have gray eyes in the F₃ generation
We know that if one parent is homozygous dominant for eye color (EE), all the offspring will have red eyes because they will inherit the dominant allele for eye color. The likelihood of gray eyes is 0%.

6. We know if both parents are homozygous recessive for the eye color gene (ee), the offspring will all have gray eyes because the only allele either parent can contribute is the recessive allele. The likelihood of gray eyes is 100 %.

7. What happens when both parents are heterozygous for eye color (Ee & Ee), or one parent is heterozygous and the other is homozygous recessive (Ee & ee)?

8. A diagram called a Punnett Square
Start with a square and divide it in half both ways

9. EE Ee ee Female E e E e Male
There were 4 ways the alleles can combine-EE, Ee, Ee, ee
3 combinations produce the dominant trait- EE, Ee, and Ee
1 produces the recessive trait-ee

10. EE Ee ee Female E e E e Male
3 out of every 4 offspring produced will have red eyes
1 out of 4 will have gray eyes
3:1—On average the ratio of red eyes to gray eyes
75% chance of red eyes
25% chance of grey eyes

11. What happens with one heterozygous parent and one homozygous recessive parent?
Female E e e Ee ee
Male

12. Female E e e Ee ee
Male
2 combinations contain the dominant red-eye allele, 2 do not
Eye color is a 50/50 chance (ratio of 2 : 2 )
On average, half (50%) of the offspring will have red eyes, and half will have gray eyes

13. Let’s Practice
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