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

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

Genotype vs Phenotype

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

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

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?

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

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

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

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

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

Trisomy 21 – Down Syndrome

The End