Mendelian Genetics Day 2

AIM: How can we tell what traits anoffspring will have?

DO NOW: Worksheet(you have 5 minutes!)

HOMEWORK: SpongeBob SquarePants exercises

A. Mendel studied many different traits of peasex. flower color, seed pod shape, pea wrinkliness

1. All of these things are controlled by alleles

What's an allele?

Allele – different versions of a gene for a trait

Mendel learned 2 things from his experiments:

1.Genes are passed from one generation to the next2.Genes come in (at least) pairs

What made him think genes were passed down?

Why did he think genes came in pairs?

Mendel realized that there aredominant and recessive traits

Dominant - can mask or hide a recessive traitRecessive - can only be seen if there are 2 recessive alleles for the trait. Otherwise, the dominant one will hide it!

*REMEMBER! Dominant does not mean better and recessive does not mean worse!*

P generation

F1 generation

F2 generation

What’s dominant here?How do we know?

What’s recessive here?How do we know?

Homozygous - the trait has two of the same alleles ex. YY or yy, BB or bb, AA or aa

Heterozygous - the trait has two different allelesex. Yy, Bb, Aa

*NOTICE* The CAPITAL letter always comes first

BUT we know there was a hiding green allele in F1 generation! What happened?!

Genotype - the pair of alleles in the DNAPhenotype - what we end up seeing in the organism

R R r r R r R r

RrRr

RrRr

RR Rr Rr rr

Rr

Rr

Rr

Rr

Punnett Squares

RR

Rr

Rr

rr

Punnett squares are used to figure out the outcome of a cross-breeding event

Do we use Punnett squares for asexual or sexual mating?

What are the alleles we use to describea female? A male?

X X

X

Y

What are the chances we have a boy? A girl?

50% chance of a girl!50% chance of a boy!

XX XX

XY XY

Summary

How can we tell what traits an offspring will have?Make sure to use the words allele, Punnett square,

genotype, and phenotype.

Discuss with your neighbor!

Homework: SpongeBob SquarePants Punnett Square worksheet!