Mendelian GeneticsMendelian Genetics

The Father of GeneticsThe Father of Genetics

• Gregor Mendel• A monk that worked with

pea genetics.– Purple vs. White - Flowers– Yellow vs. Green - Pea Color– Round vs. Wrinkled - Pea Shape– Tall vs. Short - Plant Size

• Genetics is the study of how traits are passed to offspring.

The Father of GeneticsThe Father of Genetics1. Gregor Mendel discovered that different

versions (alleles) of traits exist.

2. For each trait an organism inherits one version (allele) from each parent.

3. If the two versions (alleles) are different then one dominates over the other.

4. The two versions (alleles) separate during gamete production.

Genes and TraitsGenes and Traits

• GenesGenes code for proteinprotein that makes a traittrait.

• There can be different versions of a trait.

• EX: eye color is a traittrait.• Blue• Green• Brown

• These are different versions of the trait eye color. Different versions are called allelesalleles.

Chromosomes and GenesChromosomes and Genes

• Homologous chromosomes – one from mom and one from dad.

• Both have the same genes but each can have different alleles (different versions of the same gene).

Chromosomes and GenesChromosomes and Genes

• PhenotypePhenotype = trait = nose size

• GenotypeGenotype = gene letters = GG

• Maternal chromosome can have G or g (big or small)

• Fraternal chromosome can have G or g (big or small)

GG GGgg gggg GGGG gg

Chromosomes and GenesChromosomes and Genes

• G is dominantdominant over g

• GG or Gg = a big nose

• g is recessiverecessive under G

• gg = a small nose

• Gg = heterozygousheterozygous (different)(hybrid)

• GG or gg = homozygoushomozygous (same)(pure breed)

GG GGgg gggg GGGG gg

What kind of gametes can we get?What kind of gametes can we get?

• Gametes are made by what process?

• Meiosis!

Punnet Squares Punnet Squares • Take the genotype of both parents.• EX: father = Gg x mother = gg• During meiosis and gamete production the two

alleles are separated. (independent assortment)

Gg gg

G g g g

GG will produce

these gametes.

gg will produce

these gametes.

Which two

gametes will form a zygote?

Dominant: ( ) ______________________

Recessive: ( ) ______________________

Parents: GG X gg

Possible Sperm: ______ Possible Egg: ______

Offspring:

Genotypes: __________________

Ratio: _______________________

Phenotypes: _________________

Ratio: _______________________

Punnet Squares Punnet Squares

Dominant: ( ) ______________________

Recessive: ( ) ______________________

Parents: Gg X Gg

Possible Sperm: ______ Possible Egg: ______

Offspring:

Genotypes: __________________

Ratio: _______________________

Phenotypes: _________________

Ratio: _______________________

Punnet Squares Punnet Squares

P P F F11 F F22

• P = parents (GG gg)

• F1 = 100% Gg & big nose

• F2 = 3:1 phenotype

• F2 = 1:2:1 genotype

GgGg g

GgGg g

GG

Mom’s gametes

Dad

’s

gam

etes

GgGG G

ggGg g

gG

Mom’s gametes

Dad

’s

gam

etes

PROBABILITYPROBABILITY

• If I flip a coin. What can I get?• Heads or Tails• If I flip a coin 10 times what should I get?• 5 Heads & 5 Tails?• How many times can I get a heads?• Can I get 10 heads?

Boy or Girl? 50/50Boy or Girl? 50/50• Each time a couple mates there is a 50/50 chance of getting a boy

or a girl.

• If the same couple has 10 kids what are they most likely to have?

• 5 boys and 5 girls

• Is it possible to have 10 boys?

• Yes

• Is it likely?

• No