Introduction to

Genetics

We’ve all heard of it, but … What is genetics?

Genetics: the study of gene structure and

action and the patterns of inheritance of traits from parent to offspring.

Ancient ideas about genetics

•Selective breeding of plants and animals

Ancient ideas about genetics

•Theories why offspring resemble parents •Spontaneous generation?

•Miniature pre-formed organisms?

•Blending of “vital fluids”?

Then, in 1860…

Gregor Mendel successfully discovered genetic principles

Pea Characteristics Mendel studied traits of pea plants one at a time

Mendel and Plant Breeding

• Mendel examined thousands of crosses and offspring

• Mendel analyzed

his results mathematically- saw patterns no one else saw

Mendel’s

experiments

Mendel’s Principle Findings

•Dominant and Recessive

•Certain characteristics are dominant to others

•The dominant trait will mask another (recessive) trait, preventing it’s expression •The recessive trait “disappears” for a generation

•Law of Segregation •For each trait, organisms have 2 genes

• (which may be different versions or forms of the genes, these are called alleles)

•Each pea plant got one gene from each parent

•Genes are segregated from each other during egg or sperm formation (meiosis)

Mendel’s Principle Findings

Remember Meiosis?!? The Law of Segregation is the SAME THING! Mendel just theorized about it before it was actually discovered.

diploid (2n)

Segregation of Genes during Meiosis

meiosis I

sperm

haploid (n)

meiosis II

Bb

B

b

B

B

b

b

Mendel’s Principle Findings

•Independent Assortment • Factors for different traits are

distributed to reproductive cells independently

• Later it was seen that orientation of homologous pair to poles during meiosis is random.

• So, for example, genes from the individual’s mother don't all stay together

Click here for an animation!

Some terms …

•Trait: characteristics of an

organism passed from generation to generation. •Eye color

•Skin color

•Hair color and type

•Height

•Temperament

•Symptoms for genetic diseases

Not all traits are easy to predict… For example: polygenic inheritance. (Where have we seen the prefix “poly” before?)

Genotype

•Tells you the genetic makeup of the organism

•The genes the organism carries

Genotype •Written using symbols

•Each allele is represented by a letter

•Tall = T dominant

•Short = t recessive

•Capital letter designates the dominant trait and lower case letter designates the recessive trait.

•Capital letter is always written first.

Homozygous •An individual which contains one allele for a genetic trait

•TT-- homozygous dominant

•tt -- homozygous recessive

Heterozygous •An individual which contains different alleles for a genetic trait

•Tt heterozygote

Phenotype

•What the organism looks like

•Controlled by the genotype

•TT---------- tall

•Tt----------- tall

•tt------------ short TT Tt tt

Remember:

Example

eye color gene

Allele b

(blue eyes)

eye color gene

Allele B

(brown eyes)

Paternal Maternal

This person would have brown eyes (Bb)

Phenotype

Genotype