Genetics Notes

Gregor Mendel Father of genetics Austrian monk worked with pea plants.

Mendel derived three basic principles:

Rule of dominance in the majority of traits, one allele is dominant over the other

Law of segregation when gametes are formed, the two alleles separate; one allele into one gamete and the other allele into a different gamete.

Law of independent assortment – the alleles for different traits are inherited separately or independently of each other.

Genetics – study of heredity. Heredity – transmission of traits from parent to offspring. Traits – characteristics that are inherited.

Genes – specific portions of DNA that determine your characteristics; carry traits to be passed on from one generation to the next Allele – alternative form of a gene.

One of a pair of genes for contrasting traits Ex. R r alleles **An allele can be dominant or recessive.

Dominant allele -observed trait; will always show up; will mask (or hide) the expression of the recessive allele. ***represented with a capital letter ***dominant letter is always written first

Recessive allele – disappears; seen only when no dominant allele is present. ***represented with a lowercase letter (use the lowercase form of the same capital letter)

An offspring has 2 alleles for each trait (mother passes one gene for a trait, and the father passes the other gene for the trait to the offspring)

Genotype – gene combination of an organism; written in symbols. Examples: yy, Tt, BB, etc. Phenotype – way an organism looks; observable appearance. Examples: green, tall, hairy,

Homozygous – (pure trait) two alleles for a trait are identical (the same). Examples: TT, tt, YY, yy Heterozygous – (hybrid) two alleles for a trait are different. Examples: Tt, Yy

Example: 1 Trait = stem length, tall plants are dominant & short plants are recessive. T = tall t = short Genotype Phenotype TT tall Tt tall tt short

Example: Trait 2 =seed color Yellow seeds are dominant & green seeds are recessive. Y = yellowy = green GenotypesPhenotypes YY yellow Yy yellow yy green

Punnett square – grid used to determine the possible combinations of alleles that the parents may pass to an offspring Monohybrid cross – genetic cross involving 1 trait (2 symbols ; 4 offspring)

Steps to Solve Genetic Problems 1. Write symbols for each trait. 2.Set up cross. 3.Set up Punnett square. 4.Genotype and ratio. 5.Phenotype and ratio.

Symbols P 1 – 1st set of parents P 2 – 2nd set of parents F 1 – 1st generation of offspring (filial) F 2 – 2nd generation of offspring (filial)