Notes Chapter 11 Introduction to Genetics

11-1: The Work of Gregor Mendel

Heredity is the passing of traits from parent to offspring.

Genetics is the scientific study of heredity.

Gregor Mendel Austrian monk born in 1822 in the Czech Republic. worked with ordinary garden peas.

fertilization Gamete – specialized cell involved in sexual reproduction. Examples: -Sperm (pollen) -Egg

self pollination Single parent (true breeding). Sperm/pollen fertilize the egg cells in the same flower. The offspring are identical to the parent.

cross pollination Two parents. Hybrid- cross of traits from different parents.

Gregor Mendel prevented self pollination by cutting off the male parts of the pea flower. He cross pollinated by dusting the pollen from a selected flower onto the female part.

Trait A specific characteristic, such as seed color or plant height.

Gene- Chemical factors that determine traits. Allele- Different, contrasting, forms of a gene. Example: The gene for plant height has two different alleles available… T= tall t = short

Principle of Dominance Some alleles are dominant and others are recessive. (Think of it like a card game… sometimes one card “trumps” another. They’re both good cards, but when played together… one is dominant.)

Dominant & Recessive Practice Read the chart and determine which allele is dominant for…. -seed shape? -pod shape? -plant height? -seed color? -pod color? -seed coat color? -flower position?

But what happens to the recessive allele? Does it just “disappear”?

This is what Mendel observed when he crossed the F1 generation…. The “short” allele reappeared in the F2 generation! The “short” allele must have been present in the F1, however it was being “trumped out” & hidden by the dominant “tall” allele.

Segregation of Alleles (separation of alleles)

11-2: Probability and Punnett Squares

The likelihood that a particular event will occur is called probability, by the “flip-of-a-coin”. The principles of probability can be used to predict genetic crosses.

Punnett square T t TT Tt tt A diagram that depicts the gene combinations from a genetic cross. Alleles from one parent. T t TT Tt tt Alleles from the other parent. Possible combinations for offspring.

T t TT Tt tt homozygous – 2 identical alleles. (TT, tt) heterozygous – 2 different alleles. (Tt) Practice: Are the parents homozygous or heterozygous? What percentage of the offspring will be homozygous? Heterozygous? T t TT Tt tt

T t TT Tt tt genotype – genetic make-up (letters, Tt) phenotype – physical trait (what you see, tall) T t TT Tt tt

Genotype & Phenotype Practice T= tall t = short If the genotype is TT, what will the phenotype be? If the genotype is Tt, what will the phenotype be? If the genotype is tt, what will the phenotype be? If the phenotype is tall, what are the possible genotypes? If the phenotype is short, what is the genotype?

11-3: Exploring Mendelian Genetics

Beyond simple dominance… - some alleles are neither dominant nor recessive…

…and many traits are controlled by multiple alleles or multiple genes

Incomplete dominance One allele is not completely dominant over the other. The phenotypes appear blended.

Codominance Both alleles contribute to the phenotype of the offspring. The phenotypes are not blended… they both appear separately.

multiple alleles Genes that have more than 2 alleles.

polygenic traits Traits produced by the interaction of 2 or more genes (“having many genes”).

Drosophila fly – Thomas Hunt Morg

Other factors that can affect the phenotype of genes. - climate, soil conditions, water