Patterns of Inheritance Chapter 9

Gregor Mendel Austrian monk “Father of Modern Genetics” Famous for his work with peas

Mendel’s Peas

Cross-Pollinating

General Background Vocabulary Self-pollination: pollen from flower fertilizes the same plant True-breeds: pure gene lines – offspring match parent due to self-fertilization) Cross-pollination: pollen will fertilize a different plant Hybrid: Offspring that result from a cross between organisms with different traits; express a combination of traits from Character: heritable feature that varies among individuals (ex. seed color) Trait: possible variations for a particular character (ex. yellow seeds vs. green seeds)

Mendel’s Crosses Mendel noticed that one trait was always expressed over the other in the F1 offspring However, trait that disappeared always reappeared in about 25% of the F2 offspring.

Mendel’s Initial Conclusion Biological inheritance is determined by chemical factors passed from one generation to the next Geneticists now refer to these heritable factors as genes Genes can come in more than one form, each form is an allele ex. B or b (The “B” gene w/ 2 alleles) Additional relevant terminology: Homozygous: two identical alleles (AA or aa) Heterozygous: two different alleles (Aa) Phenotype: Physical appearance Genotype: Genetic make-up Homozygous dominant (AA) Homozygous recessive (aa) Heterozygous (Aa)

The Principles Dominance & Segregation Dominance: Certain alleles will be expressed over others, the expressed alleles are dominant to the unexpressed recessive alleles Segregation: Each parent carries two alleles for each gene. During meiosis, the pairs are separated to that only one allele is sent to the offspring in the gamete from each parent.

Genetics & Probability Probability is the likelihood of an event happening Consider flipping a coin Likelihood of flipping heads = 50% (1 of 2 possibilities) Likelihood of flipping heads twice? 50% x 50% = 25% To predict outcomes of genetic crosses we use punnett squares

The Test Cross

Exploring Mendelian Genetics Does segregation of one set of alleles influence the segregation of another pair of alleles? Mendel’s Two Factor (dihybrid) Crosses Followed two traits at a time. Same method as his original single-factor crosses Cross-pollinated to produce the F1 and allowed them to self-pollinate Mendel found that alleles for different traits did not influence each others segregation. This is referred to as the principle of independent assortment.

Pedigrees Pedigrees are like genetic “family trees”. They are used to show the inheritance of traits within families and to predict genotypes and/phenotypes of certain individuals. The following key explains the symbols and layout of a typical pedigree:

Autosomal Dominant Pedigree

Autosomal Recessive Pedigree