Genetics

Chapter 9.1

Genetics

• Genetics - the study of genes and heredity

Heredity

• Heredity – passing of traits from parents to offspring through genes

Traits

• Traits - characteristics that are inherited through genes

Gregor Mendel

• A monk in the 1800s• First to identify

heredity• Father of Genetics

Garden Peas

• Studied the traits in garden peas– Tall/short– Round/wrinkled– Green/yellow pods– Purple/white flowers

Alleles

• Each trait or characteristic has 2 copies of DNA that code for that trait

• Each copy of the trait is called an allele

• Different form of a gene

The Rule of Dominance

• Alleles can be either dominant or recessive (strong or weak)– Dominant (A) alleles are observable– Recessive (a) alleles are not usually

observable, when the dominant allele is present

Dominant

• The allele that is expressed – you can see it

• Represented by capital letters

• C curly hair

• B brown hair

Recessive

• The allele that is not expressed when covered up by the dominant allele– It is there you just cannot see it

• Use the lower case for the recessive allele

• c for straight hair• b blonde hair

Genotype

• The copies of alleles or genes that an organism has

• BB, Bb, bb/ TT, Tt, tt

Phenotype• The way an organism physically looks

– Brown hair, tall

Homozygous (homo = same)

• Pure

• When an organism has 2 copies of the same allele

• BB – homozygous dominant

• bb – homozygous recessive

Heterozygous (hetero = different)

• Hybrid

• When an organism has 2 different alleles for a gene

• Bb, Gg, etc.

The Law of Segregation

• Alleles for a gene separate when forming a sperm and egg

Law of Independent Assortment

• Alleles for different genes are distributed to sperm and egg independently

• Could be – tall and fat– short and thin– tall and thin– short and fat

• This is why all siblings do not look exactly alike

So…