Mendel’s GeneticsMendel’s Laws Apply to Genes on

Separate Chromosomes

Where are our genes?• Chromosomes are made of DNA and

contain genes that have different versions or alleles. Combinations of genes make up our traits or characteristics.

3 Laws Mendel Studied about our

Genes

• Law of Segregation

• Law of Dominance

• Law of Independent Assortment

Law of Segregation

• Gametes get one copy of each homologous chromosome

• What would happen if you got less or more than one?

Segregation of Sex Chromosomes

• Males are XY and Females are XX

• All eggs contain an X• Sperm either contain an X

or Y• SRY gene on Y

Chromosome makes youForm testes and appearmale

Probability can be shown with a Punnett Square

• Probability is a prediction based on what is known.

• Actual results can deviate from what is expected.

• Probability resets each time.

• A couple has 5 girls and are pregnant again. What is the probability that their 6th kid is a boy?

Karyotype

• Chart organizing chromosomes in developing embryo.

• Cells taken from placenta in process called amniocentesis

• See if you can determine:– Sex– Health

Normal Male Normal Female

Trisomy 21 (Down’s Syndrome) Turner’s Syndrome

More Necessary Vocabulary

• Genotype: Combination of alleles (Letters)

• Homozygous: Both letters represent same allele (aa, AA)

• Phenotype:

How and organism looks.

• Heterozygous: Hybrid, or both alleles (Aa)

Law of Dominance

• Dominant (capital letters) traits overpower recessive traits (lowercase letters).

• Dominant traits are NOT more common! Example: Polydactly

Punnett Square: Shows outcome of mating between to individuals

Let’s use Mendel’s Peas to Practice! Dominant Traits are shown first

Easy• A smooth pea

whose genotype for seed shape WW is crossed with a seed that is wrinkled ww. – Will their offspring

be wrinkled or smooth?

– What will be the % of the genotypes of their offspring?

Medium• Two tall pea plants

were crossed and they ended up with the following results:75% tall offspring; 25%

short offspring.

What are the genotypes of the parents?

Hard• Two pea plants are crossed and 80 seeds are produced. Of those 80 seeds, 46 produce purple flowers and 34 produce white flowers.

Use a Punnett Square to show if this is possible.

What are the genotypes and phenotypes of the parents?

Mendel’s Law of Independent Assortment

• Homologous chromosomes line up randomly during meiosis and therefore many different gene combinations can be produced.

Back to Mendel’s Peas

• A pea homozygous recessive (wrinkly green) for the traits shape and color is crossed with a homozygous dominant (smooth yellow) plant

• What will the F1 (first generation) look like?

• What will the second generation look like?

First..Find the parental genotypes

• First Generation

– Homozygous Dominant

– Homozygous Recessive

Second FOIL for gametes

• First Generation– Parent 1: SSYY

– Parent 2: ssyy

Make a 16 box Punnett Square, one parent on each side, two letters on top of each box, 4

letters inside each box!

Analyze Data

• What are the expected portions of each phenotype?

Generation 2

• Parent 1:

• Parent 2:

Foil for Gametes• Parent 1:

– F– O– I– L

• Parent 2:– F– O– I– L

Punnett Square…2 letters above each box, 4 letters in each box

Analyze for independent assortment

of phenotypes

Corn Activity

• You will determine if your baby corn, belongs to the parent corn!

• The Punnett Square is hypothesis showing probability, you must determine if the actual results match the expected results!