Genetics & Heredity Mendel and His Peas

Gregor Mendel Heredity – the passing of traits from parents to offspring Gregor Mendel – “father of genetics” Austrian monk performed experiments on peas to help answer questions about genetics Genetics – the study of how traits are passed from parents to offspring

Mendel’s First Pea Experiment Cross-pollinated Purple flowers x purple flowers = all purple flowers White flowers x white flowers = all white flowers Purple flowers x white flowers = all purple flowers

Mendel’s Second Pea Experiment Self-pollinated the hybrid flowers from the first generation (the offspring that were a result of the purple flowers x white flowers) Results: some offspring were purple and some were white

Mendel’s Conclusions Dominant and Recessive Dominant Trait a genetic factor that blocks another genetic factor (ex. purple color (P)) Recessive Trait a genetic factor that is blocked by the presence of a dominant factor (ex. white color (p)) recessive trait is observed only when two recessive genetic factors are present in offspring (pp)

Ratios A comparison of two numbers or quantities by division Try it: The ratio of purple to white flowers in Mendel’s second experiment is 3 to 1 or 3:1 or 3/1 Try it: There are 14 girls and 7 boys in a classroom. What is the ratio of girls to boys? Boys to girls?

Inheritance

Genes & Alleles Gene – a section on a chromosome that has genetic information for one trait ex. flower color Allele – the different forms of a gene ex. purple, white

Genotype & Phenotype Phenotype – how a trait appears, or is expressed ex. purple flowers, blue eyes, red hair Genotype – the two alleles that control the phenotype of a trait expressed as letters uppercase for dominant lowercase for recessive

Homozygous and Heterozygous Homozygous – when the two alleles of a gene are the same homozygous dominant - purple flowers (PP) homozygous recessive - white flowers (pp) Heterozygous – when the two alleles of a gene are different ex. purple flowers (Pp)

Punnett Squares Punnett square – a model used to predict possible genotypes and phenotypes of offspring expressed as a probability (percent chance) Phenotype: Green = 75% Yellow= 25% Genotype: GG = 25% Gg = 50% Gg = 25%

Punnett Square Examples

Draw a Punnett square for the following breeding pair of frogs: Gg x Gg If green skin (G) is dominant to yellow skin (g), what is the probability of the offspring being green?

Try Some Punnett Squares: Brown eyes (BB) x Blue eyes (bb) Freckles (Ff) x no freckles (ff)

Pedigree Pedigree – a chart that shows phenotypes of genetically related family members Symbols: MALE FEMALE Homozygous Dominant Heterozygous Homozygous recessive

Pedigree Example

Patterns of Inheritance

Types of Dominance Incomplete Dominance – when the phenotype of an offspring is a combination of the parents’ phenotype ex. white flower x red flower = pink flower Codominance – when two alleles can be observed in a phenotype ex. white cow x black cow = spotted cow

Other Patterns of Inheritance Multiple Alleles genes with more than two alleles ex. blood type (A, B, AB, O) Sex-linked Traits alleles found on the sex chromosomes (X, Y) Polygenic Inheritance when multiple genes determine the phenotype of a trait ex. height