The study of... Traits that can be passed on from parents to offspring

Inheritable traits include eye and skin colour, nose shape, height, etc.

Cells – basic building block for all living things

Genes are: • structures inside cells• carry traits from one

generation to another. • made of DNA.• strung together to form

long chains of DNA coiled in structures called chromosomes

• like blueprints for a house. In living things, these are the plans for building cells, tissues, organs, and bodies.

Aristotle• Inheritance based on

blood• Blood of parents mixed

to produce offspring’s characteristics (blood relatives, pureblood, bloodlines, etc.)

After discovery of sperm and eggs...• A tiny person existed in

sperm/egg• Once implanted, the tiny

sperm grew into a person

• Egg and sperm contained sample cells from all body areas

All organisms made of similar units called cells1) Cells come from

pre-existing cells (not spontaneous generation)

2) Cells are unit of structure and function in living things

3) Cells contain hereditary information which is passed onto other cells

Genetic Terms Phenotype – the physical

expression of a gene (E.g.tall, short, green, yellow)

Genotype – the genes that are present in a pairing (E.g. Tt, TT, or tt)

Dominant – gene whose presence “masks” the appearance of the recessive gene (E.g. Tt = tall plant)

Recessive – gene whose presence is “masked” by the dominant gene. Recessive genes are only expressed when both alleles are present (E.g. tt = short plant)

Genetic Terms Homozygous – when

pairs of genes are the same (e.g. TT or tt)

Heterozygous – when pairs of genes are different (e.g. Tt)

Alleles – Different forms of genes. E.g. There is an allele for tall plants (T) and an allele for short plants (t)

Genetic Terms

F1 generation – offspring from the cross of two true breeding parents (parents that are TT and tt)

F2 generation – offspring from the self-fertilization of F1 offspring (3:1 ratio of Tall to short)

Monohybrid cross- a genetic cross that looks at one traits at a time (e.g. eye colour)

Gametes – Sex cells (egg and sperm)

The basic laws of heredity were first formed during the mid-1800’s by an Austrian botanist monk named Gregor Mendel. Because his work laid the foundation to the study of heredity, Mendel is referred to as “The Father of Genetics.”

Mendel was interested in finding out why some pea plants were tall, some short, some with yellow seeds, and some with green seeds.

He used pea plants because they were:• easy to grow• short life cycles• able to self-pollinate or

artificially pollinate• possessed opposing

characteristics (short vs. tall, green vs. yellow)

Started with pure breeding parents (plant that reproduce exact copies of themselves generation after generation)

He took pure breeding parents for one trait (i.e. Short stem) and crossed them with pure breeding parents for another trait (i.e. Tall stem)

All offspring were tall These offspring were

called the F1 or first filial generation

t t

T Tt Tt

T Tt Tt

In his second experiment, Mendel allowed individuals of F1 generation (all Tall) to pollinate themselves

Result = Some individuals were short and some were tall. How did this happen?

These second generation individuals were referred to as the F2 or second filial generation

P p

P PP Pp

p Pp pp

Mendel’s Laws of Heredity Law #1

• Traits were controlled by pairs of “factors” with one “factor” coming from each parent

• Today we call “factors” genes.

• Different forms of genes are called alleles

• E.g. there is one allele for tall plants (T) and another allele for short plants (t)

Mendel’s Laws of Heredity Law #2

• Called Principle of Dominance and Recessiveness

• States that one factor (gene) in a pair may mask (or overtake) the other, preventing it from having an effect.

• “Stronger” genes were called dominant and the genes that were masked were called recessive

Mendel’s Laws of Heredity Law #3

• Law of segregation• States that members of a

pair of factors (genes) are separated during the formation of gametes

• This means one allele (T) is present in the egg while another allele (t) is present in the sperm. When the egg and sperm combine, the individual has genes Tt.

Law #4• Called Law of

Independent Assortment• States that gene pairs

separated from each other and were distributed to gametes independently of each other

• E.g. gametes of stem length separated independently from gametes of flower colour.

Mendel’s Laws of Heredity