The scientific study of heredity. Genetics The scientific study of heredity.

Vocabulary: Make sure to DEFINE these words as you go through the notes Heredity Phenotype Variation Genotype Dominant DNA Recessive Allele Purebred Meiosis Hybrid Homozygous Heterozygous

What is Heredity ? The passing of traits from parents to their offspring Traits are passed to you through your parent’s sperm and egg 50% of DNA from mom, 50% from dad Variation (differences in people’s traits) are due to the combination you inherit

1860s: Gregor Mendel “Father of Genetics” (he was an Austrian monk) He figured out how traits are passed on before we knew about DNA, or chromosomes or meiosis

To begin, Mendel created pure breeding plants all pure purple Purple white all pure white

First Cross: pure purple with pure white Cross fertilized P (Parental) generation Pure purple with pure white P Generation F1 Generation purple white X All purple

Second Cross: Cross 2 F1 plants Cross fertilized two of the offspring of the F1 generation purple purple purple purple X purple white These were the F2 This was always 3:1 ratio or out of 929, 705 : 224

Mendel’s Experiments led him to 3 Laws of Inheritance The Law of Dominance The Law of Segregation The Law of Independent Assortment

The Law of Dominance: Each individual has TWO factors for each trait known as alleles Some alleles dominate over others – the dominant allele is expressed in the offspring Homologous chromosomes-same traits -different forms These are alleles Freckles No Freckles Dimples No dimples Tongue roller Non-roller From Mom From Dad

Alleles are: Represented by a letter of the alphabet Capital = dominant allele A lowercase = recessive allele a Each allele corresponds to a gene on a chromosome - the alleles represent different forms of the gene

Law of Segregation The two alleles for each trait separate and move into different gametes – meiosis Since only one egg or one sperm will contribute to the new offspring, only one allele for a trait is passed on The chance that any allele will be passed on is 50%

Law of Independent Assortment the inheritance of alleles for one trait doesn’t affect the inheritance of alleles for another trait - occurs in meiosis during metaphase 1

Meiosis: division of the sex cells

Genotype: Genotype is the combination of alleles for a trait expressed with letters Homozygous dominant (purebred) TT - two capital letters Heterozygous (hybrid) Tt - one of each letter (big and small) Homozygous recessive (purebred) tt - two lower case letters

Phenotype: Phenotype is physical expression of the genotype. (how it looks) Genotype Phenotype TT tall plant Tt tall plant *dominant allele always is expressed over the recessive allele tt short plant *recessive trait is expressed only if there is no dominant gene

If R = red, and r = white What is the genotype of homozygous dominant? What is the heterozygous genotype? Rr What is the homozygous recessive genotype? rr

If R=red and r =white What is the phenotype of of RR? What is the phenotype of Rr? What is the phenotype of rr? White

If two parents are crossed (TT X tt), what are the resulting offspring? You can determine phenotypes using a Punnet square. T T parent Tt Tt t Genotypes: 4 Tt Tt Tt Phenotypes: 4 Tall t This is the first or parent generation parent

Now try on your paper a cross of two of the offspring from the parent generation. This is called the first generation or the F1. T t T Tt TT Tt tt t Genotypes: 1TT: 2Tt : 1tt Phenotypes: 3 Tall: 1 Short.