Mendelian Genetics Ch. 6

What is Genetics? The study of the inheritance of traits and variation in organisms. Trait: characteristics that are inherited (eye color, height, leaf shape, etc.)

GREGOR MENDEL Mendel is known as the “Father of Genetics.” He was an Austrian monk & studied pea plants in the monastery garden.

Mendel’s Experiments: Mendel worked with pure breeding (self-pollinating) pea plants He controlled breeding between plants He studied 7 different traits of pea plants: pea shape, pea color, pod shape, pod color, plant height, flower color, and flower position First experiments were monohybrid crosses (cross one trait at a time)

Mendel’s Experiments: P Generation Tall Short True-breeding

Mendel’s Experiments: F1 Generation Tall Tall 100% tall

Mendel’s Experiments: F2 Generation Tall Tall Tall Short Ratio = 3 talls to 1 Short

Mendel’s Experiments: Mendel observed the same results every time he crossed two different forms of a trait. P Generation F1 Generation F2 Generation Short Tall Tall Tall Tall Tall Short Tall

Mendel’s Conclusions: 1. Biological inheritance is determined by factors (or GENES) that are passed from one generation to the next.

2. Law of Segregation: Organisms inherit 2 copies of each gene (one from each parent) When gametes (egg & sperm) are formed the pair of genes responsible for each trait separate.

3. “Principle of Dominance” – some alleles are dominant and some are recessive. The dominant trait prevents the expression of the recessive trait.

An allele is a different form of the same gene Each parent donates one allele for every gene. Homozygous: two alleles are the same (GG or gg) Heterozygous: two alleles are different (Gg)

Alleles can be represented using letters. dominant allele: expressed when at least one copy is present; capital letter (GG or Gg) recessive allele: expressed only when two copies are present; lowercase letter (gg)

All of an organism’s genetic material is called the genome. Genotype: genetic makeup (Bb vs. bb) Phenotype: physical traits (brown eyes vs. blue eyes)

Probability The likelihood that an event will occur Probability is used to predict outcomes of genetic crosses Ex: flipping a coin What is the probability that it will land on heads?

Punnett squares are used to predict genetic crosses. The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. Axes = gametes of parents Boxes = genotypes of offspring

Monohybrid crosses examine the inheritance of only one specific trait. Examples: Cross a homozygous dominant with a homozygous recessive:

Cross one heterozygous with another heterozygous

Cross a heterozygous with a homozygous recessive

Terms to Know!! Gene Allele Dominant Recessive Homozygous Heterozygous Genotype Phenotype