1. Important Terms Genotype type of genes (ex: Tt) Phenotype
traits (ex: tall)
Homozygous
Two of same allele (ex: TT or tt)
Heterozygous
One of each allele (ex: Tt)
Dominant
Gets expressed; use capital letter
Recessive
Gets covered; use lowercase letter

2. Punnett Square Basics Parent genotypes listed on edges
Fill in spaces…big letter listed first
List genotype (G) and phenotype (P) including fractions or percents
G: 4/4 Aa
P: 4/4 red

3. Genotype vs Phenotype

4. Cross 2 heterozygous tall, purple pea plants with each other…
(T=tall, t=short, P=purple, p=white)

5. Cross 2 heterozygous tall, purple pea plants with each other…
(T=tall, t=short, P=purple, p=white) TP Tp tP tp

6. Cross 2 heterozygous tall, purple pea plants with each other…
(T=tall, t=short, P=purple, p=white) TP Tp tP tp
TTPP
TTPp
TtPP
TtPp
TTpp
Ttpp
ttPP
ttPp
ttpp
How many different phenotypes is that?

7. Cross 2 heterozygous tall, purple pea plants with each other…
(T=tall, t=short, P=purple, p=white) TP Tp tP tp
TTPP
TTPp
TtPP
TtPp
TTpp
Ttpp
ttPP
ttPp
ttpp
P: 9/16 tall, purple 3/16 short, purple
3/16 tall, white 1/16 short, white

8. Which other pattern does this reflect?
Multiple Alleles
Some traits have more than 2 possible alleles
Ex: Human blood has A, B, and O
Which other pattern does this reflect?
codominance

9. Polygenic Inheritance
Due to more than one gene controlling a trait
Has an “additive effect”
Ex: human eye color, skin color, hair color, height

10. Sex-linked Gene Inheritance
In humans, sex-linked genes are the ones on the X chromosome
Fathers pass these on to their daughters only
Mothers pass these on to both sons & daughters
Males more likely to have recessive sex-linked traits

11. Sex-linked Inheritance
Ex: male-pattern baldness; hemophilia; color-blindness

12. Trisomy 21 – Down Syndrome

13. The End