Genetics The study of heredity - how traits are passed from parent to offspring or x = or

The study of heredity started with the work of Gregor Mendel and his pea plant garden Mendel was an Austrian Monk that lived in the mid 1800’s

Why did Mendel work with pea plants? Fast to grow Easy to cross pollinate Two distinct forms for traits Tall or short Yellow or green pods Smooth or pinched pods Yellow or green peas Round or wrinkled peas Colored or white seed coats Side flowers or end flowers

Mendel’s cross between tall pea plants yielded all tall pea plants Mendel’s cross between tall pea plants yielded all tall pea plants. His cross between short pea plants yielded all short pea plants. X = X = Mendel’s cross between tall pea plants and short pea plants yielded all tall pea plants. x =

Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being short. x =

Mendel’s Factors Mendel repeated this experiment with many pea plants with many different traits For each, he discovered that there seem to be “factors” that disappeared in one generation and then reappeared in the next This went against the idea that an organism is a blend of their parents’ traits

Why was Mendel’s work so important? Mendel worked at time when microscopes were not very good and the cell theory was only just being thought of When scientists understood DNA and chromosomes, they understood how important his work with pea plants was

Dominant vs. Recessive Genes There are TWO basic kinds of genes: Dominant - A gene that is always expressed and hides others Represented with a capital letter Recessive - A gene that is only expressed when a dominant gene isn’t present Represented with a lowercase letter

A Human Example A dominant gene will always mask a recessive gene. Eddie Munster A dominant gene will always mask a recessive gene. A “widow’s peak” is dominant, not having a widow’s peak is recessive. If one parent contributes a gene for a widow’s peak, and the other parent doesn’t, the off- spring will have a widow’s peak.

Latin Roots All organisms have two copies of each gene: one contributed by the father and the other contributed by the mother. Homozygous - Two copies of the same gene “homo” - same Heterozygous - Two different genes “hetero” - different

Genotypes and Phenotypes For the widow’s peak: Genotypes: WW, Ww, or ww Phenotypes: widow’s peak or no widow’s peak WW - has a widow’s peak Homozygous dominant Ww - has a widow’s peak Heterozygous ww - no widow’s peak Homozygous recessive

Eddie Munster’s Parents Father = Herman - No Widow’s Peak Mother = Lilly - Has a Widow’s Peak

What can you determine about a genotype from a phenotype? Since Herman has no widow’s peak, he must be “ww”, since Lilly has a widows peak she could be either “WW” or “Ww” Definitely ww Homozygous recessive Either Ww Heterozygous or WW Homozygous dominant

Punnett Squares A Punnett Square is a tool used to predict the possible gene combinations of the offspring. In this case, we can work backwards… A Punnet Square begins with a box 2 x 2 One gene is called an “allele” One parents pair is split into alleles on top, the other along the side Each allele is crossed with the other allele to predict the traits of the offspring Assume Lilly is heterozygous Ww W w Assume Herman is homozygous recessive ww w Ww ww w Ww ww

How can you tell? So which is true? Is Lilly homozygous dominant (WW) or is she heterozygous (Ww)? W w W W w Ww ww w Ww Ww w Ww ww w Ww Ww

More Information Needed Recall that Herman and Lilly had another offspring, Marylin. She had no widow’s peak. Therefore, Lilly must be heterozygous.

Incomplete dominance Two forms blend

Co-dominant Traits both forms are shown

Multiple Alleles more than two forms of a trait

Polygenic Traits Controlled by many genes