Mendelian Genetics

Father of Modern Genetics

• Austrian monk, high school teacher, and part-time garden keeper

• First to propose biological inheritance of traits

• Work not recognized until after his death

Gregor Mendel

Why pea plants?

• It’s what he had• They grow fast• Pea plants are true

breeding• Gregor noticed that one

stock of seed would produce only tall plants and another only short plants

Traits…

• Specific characteristics that vary from one individual to the next– Hair color– Eye color– Seed color– Flower color

P generation

Cross-pollination

Next, Mendel wanted to find out if the white alleles had disappeared, or were they still present in the F1 generation.

Mendel’s Experiment

Vocabulary…

• P generation: parental• F1: “first son” – the offspring of the P

generation• F2: “second son” – the offspring of the F1 cross• Phenotype: the physical characteristics, what

the trait “looks” like• Hybrid: cross between parents with different

versions of the trait.

• Mendel crossed the F1 generation with itself

• He found that the white flower trait reappeared in some of the F2 generation

Perplexed?

• Conclusion One: inheritance is due to factors that are passed from one generation to the next– Today, we call those factors GENES– Allele: different forms of a gene (like pink vs white

for flower color)

• Conclusion Two: some alleles are dominant and others are recessive

How did the white trait “reappear”?

• He proposed this was due to segregation of alleles during formation of gametes.

What are these called?!

What are these called? What process made them?

• Homozygous: two copies of the same allele– Dominant: AA– Recessive: aa– TRUEBREEDING

• Heterozygous: different alleles (Aa)

Practice: Cats

1. What trait is represented by “T” and “t”?2. “NN” = phenotype or genotype?3. Long hair = phenotype or genotype?4. A homozygous tabby cat would have what

genotype?5. A cat that is “nn” would have what

phenotype?

Applying and practicing your vocab

• Crazy Traits• Exit Slip

• Vocab quiz on Wednesday

Probability

• Mendel categorized and counted the many offspring of each of his experiments.

• He noticed that each time he repeated a particular cross he obtained similar results.

For example:Every time he crossed two

plants that were heterozygous for stem height (Tt), about ¾ of the offspring were tall and ¼ were short.

Probability and Punnett Squares

• Punnett squares are used as a tool to predict this probability

• Monohybrid crosses can be performed to determine probability of phenotype for one particular trait

Genotypes

AAAa

aa

Homozygous Dominant

Heterozygous

Homozygous Recessive