GENETICS & HEREDITY

Mendel and His Peas

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

Gregor Mendel

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)

A comparison of two numbers or quantities by division 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?

Ratios

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