Mendel and Heredity Ch Genetics

Genetics Study of Heredity Passing of traits from parents to offspring Trait: a specific characteristic

Gregor Mendel Father of genetics Parents were farmers He became ordained as a priest Studied science & math at Univ of Vienna

Mendel’s Experiments Chose Pea plants as exp. Subjects –Easy to cross –Grow quickly –Produce high number offspring –Showed variety of contrasting traits Purple vs white flowers Tall vs short stems Round vs wrinkled seeds

Mendel’s experiments cont. 1.Chose true breeding lines of each plant/trait he studied. a.True breeding always produced offspring of the same type 2.Crossed a true breeding plant with a plant of the opposite trait. (purple x white) a.Called this the Parental (P) generation

3.Recorded data on the offspring of this cross. (hybrid) 3)First Filial generation (F1) 4.Self pollinated the F1 offspring 5.Recorded data on the offspring of the 2 nd generation. 5)Second Filial generation (F2)

Analysis: F1 Generation Always displayed one trait (he later called this the dominant trait) Must have within it the trait from the original parents – the white trait

Analysis: F2 Generation Displayed the hidden trait, ¼ of the F2 gen. had it (he later called this hidden trait the recessive trait) Each individual has 2 ”factors” that determine what external appearance the offspring will have –These factors are now called genes or alleles

Mendel established 3 principles or laws from his research

The Principle of Dominance and Recessiveness One trait is masked or covered up by another trait

Principle of Segregation The 2 factors (alleles) for a trait separate during gamete formation

Principle of Independent Assortment Factors of a trait separate independently of one another during gamete formation.

Example: Whether a flower is purple has nothing to do with the length of the plants stems – each trait is independently inherited.

Modern Genetics Mendel’s factors are now called Alleles. (different versions of a gene) –For every trait a person has, 2 alleles determine how that trait is expressed

We use letters to denote alleles, since every gene has 2 alleles, all genes can be represented by a pair of letters PP = purple, Pp = purple pp = white

Terms to know: Homozygous: When the alleles are the same. (true breeding) Ex. AA, bb, EE, dd

Terms to know: Heterozygous: When the alleles are different. (dominant allele is expressed) Ex. Pp, Aa, Bb

Terms to know: Genotype: Letters used to denote alleles (BB, Pp, aa)

Terms to know: Phenotype: What an organism looks like. (brown, purple, curly hair….)

Terms to know: Monohybrid cross: a cross involving one pair of contrasting traits. Ex. Pp x Pp

Terms to know: Punnett Square: Used to determine the Probability of having a certain type of offspring given the alleles of the parents.

How to solve a Punnett Square: 1.Determine the genotypes (letters) of the parents. 1.(AA x aa ) or (Rr x Rr) 2.Set up the punnett square w/one parent on each side. 3.Fill out the punnett square middle. 4.Analyze the number of offspring of each type.