Gregor Mendel and his peas…Austrian Priest and

teacher who tended the gardens.

Experimented with fertilization.

Plants can reproduce two ways.

1. Self pollination – fertilize themselves

2. Cross pollination – male x female (different plants)

Mendel’s experiment

Mendel crossed many different traits in pea plants and recorded his results.

He did 4 unique things in his experiment

1. Counted only one trait at a time

2. Used large numbers of data to off set chance

3. Did many identical experiments and combined results

4. Used probability to analyze results

A gene is a section of DNA that forms a trait.

For example: Hair color, Height, ear lobes….

Alleles are different forms of a gene.

For example: brown hair, blonde hair or Tall and short.

You get one allele for each trait from your parents…

You get one allele from each of your parents in the egg and sperm.

Dominant allele – the allele that “wins”. We use a capital letter “R”

Recessive allele – the allele that is hidden or loses . We use a lower case letter “r”.

Lets pretend that… R = can roll their tongue r = can’t roll their tongue

RR = Dominant, Dominant - HomozygousThis person can roll their tongue

Rr = Dominant, recessive – Heterozygous (hybrid)

This person can roll their tonguerr = recessive, recessive - Homozygous

This person can’t roll their tongue

Each gamete (sperm or egg) cell has one allele for a trait.

When they fertilize, the two alleles are joined – (remember most basic traits need two alleles)

The dominant alleles will always be expressed

If there are two recessive alleles, then the recessive form of the trait will be expressed.

Once you do your Punnett Square, the letters (alleles) are called the Genotype.

Example: RR, Rr, rr

The Phenotype is what the physical trait actually looks like (words)

Example: can roll tongue, blond hair, blue eyes, etc.

4 steps

1. Make a box2. Put the

genotypes of the parents on the outside.

Lets say that you were crossing a heterozygous tongue rolling mom with a dad who can’t roll his tongue.….Steps one and two would look like this……

T

t

t t

Steps, cont’d3. Fill in the box4. Figure out the genotype

and phenotype of the offspring.

Genotype - lettersTT 0%Tt 50%tt 50%

Phenotype - appearance50% can roll tongue50% can’t roll tongue

Tt Tt

tt tt

T = Tall persont = Short

personCross: Tt X Tt

Figure out genotype and phenotype.

B = Brown Hairb = blonde hairCross a homozygous brown haired man with a

heterozygous brown haired female. What are the genotype and phenotype of their possible offspring?

Genotype:BB = Bb = bb = PhenotypeBrown hair = blonde hair =