1. Genetics: Punnett Square Notes
First…some vocab!

2. Let’s Review… What is heredity? What is a gene? What is an allele?
The passing of traits to offspring
What is a gene?
A specific section on a strand of DNA that codes for a certain trait
What is an allele?
Different versions of a gene

3. Vocab: Trait- physical characteristic that we see
Dominant- expressed allele (overpowers and covers up recessive allele, if present)
Recessive- unexpressed allele (covered up by dominant gene)

4. Phenotype- the physical appearance of a trait in an organism
Genotype- the genes of an organism; for one specific trait we use two letters to represent the genotype.
Uppercase letter= dominant allele
Lowercase letter= recessive allele.
Phenotype- the physical appearance of a trait in an organism

5. Homozygous- two same alleles (2 dominant or 2 recessive) [purebred]
Heterozygous- two different alleles- 1 dominant and 1 recessive
[hybrid]

6. Tt QQ Ff rr Yy hh mm Ss GG PP Ll Bb dd
Underline the following that are homozygous and circle the ones that are heterozygous:
Tt QQ Ff rr Yy hh mm Ss GG PP Ll Bb dd

7. B= brown eyes b= blue eyes
What would the genotype be for an individual who is heterozygous? ______
What would be the phenotype be for an individual who is heterozygous? _________
If a person has blue eyes, what must their genotype be? _______ Bb
Brown eyes bb

8. Punnett Square What is it?
A diagram used to predict the probability of traits being passed from parents to offspring.
What do I need to know before doing a Punnett Square?
Both parents’ genotypes for that trait (Tt x tt)
Does the Punnett Square guarantee anything??
No! It just predicts the probability of traits being passed on to offspring.

9. Important Note! Probability is NOT influenced by previous results
Each offspring has the exact same chance of getting a trait as previous offspring
Ex: every time a baby is born, there is a 50% chance of being a boy or a girl.

10. Step-by-Step Punnett square review
1st. Draw your square
Parental Cross: Tt x tt

11. 2nd. Then place the parent’s genotypes on the outside
2nd. Then place the parent’s genotypes on the outside. Each allele goes next to its own box!!
Parental Cross: Tt x tt

12. T t t t 3rd. Complete the square. (“Drag & Drop”)
Parental Cross: Tt x tt
3rd. Complete the square. (“Drag & Drop”) T t t t

13. Genotypes (letters): Phenotypes (physical appearance):
4th. Summarize your results, using percentages.

14. Sample Problem #1
1. An elephant with large ears (EE) is crossed with an elephant with small ears (ee). What are the expected offspring?

15. Sample Problem #2
2. A heterozygous white chicken, which is the dominant allele, is crossed with a red chicken (recessive). What is the probability of having a red chicken?

16. Now it is your turn! Refer to vocab list as you work
You must show a completed Punnett Square for each problem.
Answer Key will be posted on screen in a few minutes

17. Answer Key- check yourself!
1. BB x bb G: 100% Bb P: 100% Black bulls 2. Pp x pp G: 50% Pp, 50% pp P: 50% horned, 50% polled 3. Ss x Ss G: 25%SS, 50%Ss, 25%ss P: 75% Large, 25% Small
First Generation- SS x ss
G: 100% Ss
P: 100% Long hair
Second Generation- Ss x Ss
G: 25%SS, 50%Ss, 25%ss
P: 75% Long, 25% short
“Genetic Problem Solving” wkst is due TOMORROW.