GENETICS CH. 12 (and 10.1)

Origins of Genetics: Gregor Mendel: Father of Modern Genetics 1. Austrian monk 2. Spent 14 yrs. Working in the monastery, taught high school, and was also in charge of the garden. 3. Changed biology forever with his work.

Mendel’s Breeding Experiments Bred different varieties of the garden pea in an attempt to understand heredity. Useful Features of Peas:  Several traits show different forms (alternating) Ex. Tall/Short, Yellow/Green  Self-pollinating & Cross-pollinating  Easy to grow  Produce many offspring  True-breeding – if allowed to self-pollinate they would produce offspring identical to themselves.

The Origin of Genetics Mendel cross-pollinated two different plants with different characteristics and then studies the results (cross-bred). Trait – specific characteristics that varies from one individual to another. By studying two contrasting characteristic plants and their offspring he created hybrids (heterozygous). Biological inheritance is determined by factors that are passed from one generation to the next. Gene- chemical factor that determines traits (segments of DNA that code for proteins!)

Genetic Principles: Alleles – different forms of a gene. Ex. Height – Tall (T) & Short (t) Discovered the principle of dominance – some alleles are dominant and others are recessive. Rules:  The dominant allele for a particular trait will ALWAYS exhibit that form of the trait.  Recessive alleles will only be shown when the dominant allele is NOT present.

RESULTS: Crossing 2 parents that were true bred (either fully dominant or fully recessive) created offspring that all showed the dominant trait. Example: flowers PP (purple) x pp (white) P P Pp p p

RESULTS: p Second generation crossing Pp x Pp created a 3:1 ratio of purple to white flower plants Purple – 75% White – 25% PP – 25%, Pp – 50%, pp – 25% P PP Purple Pp purple white P p

Mendel’s Theory: 1) Hypothesis: Different versions of a gene are called alleles. An individual usually has 2 alleles for a gene, each inherited from a different parent. 2) Individuals with the same two alleles for a gene are homozygous. 3) Individuals with the two different alleles are heterozygous for that trait.

GENOTYPE & PHENOTYPE 4) Genotype & Phenotype: The set of alleles that an individual has is called its GENOTYPE (G = GENETIC) The physical expression of a trait or outward appearance of the genotype is called the PHENOTYPE (P = PHYSICAL) Ex. Bb – genotype (B-brown, b-blue) Brown - phenotype

Laws of Heredity: Law of Segregation: The different alleles for a trait separate when gametes are formed. Law of Independent Assortment: The genes for different traits can segregate independently during the formation of gametes. Both laws account for the many genetic variations of organisms.

Laws of Heredity

Punnett Squares Punnett Squares: Show the different gene combinations that might result from a genetic cross. Used to predict and compare the genetic variations that will result from a cross. Probability can be used to predict the outcomes of a cross (% and ratios). Monohybrid cross – compares the outcome of 1 set of alleles or 1 trait. Dihybrid Cross – compares the outcome of 2 sets of alleles 2 traits.