Chapter 10: Mendel and

MeiosisSeptember 28 2010

Who is this Mendel Guy anyway?•Austrian Monk in 1800’s- 1st to determine how traits are transferred from parent to offspring

- FATHER OF GENETICS, given credit after he died

- Named the gene- Formulated three laws

What did he Discover?1. Law of Segregation: two alleles for a trait segregate (separate) during meiosis.

Out of the two alleles that are present, only one is present in the gamete.

B <-- Bb --> b

2. Law of Dominance: one gene of a pair may dominant the expression of another

TT - tall - Homozygous Tall, DominantTt - tall - Heterozygous Tall, Dominanttt - short - Homozygous Short, Recessive

3. Law of Independent Assortment: each pair of alleles separates independently of each other pair during gamete formation

How did he figure this out?

By following two separate alleles through time, he was able to identify that there was no connection of two of more traits being inherited together.

What type of trait is that?

When an organism carries two of the SAME alleles, it is considered homozygousWhen an organism carries two DIFFERENT alleles the organism is known as heterozygous

There are two types of traits known as dominant or recessive. Each parent passes along one to its offspring. It is

these traits that determine an organism’s appearance

A DOMINANT trait trumps a RECESSIVE one.

TTBBBbttbbPpRR

Examples:

Vocabulary:Genotype: The genetic makeup or set of alleles of an organism

Phenotype: The physical and physiological traits of an organism, which are determined by its genetic makeup.

Who would have thought…Peas could have such a huge impact on genetics as we know it today!Why the Pea Plant?•Easy to grow• Simple fertilization• Many possible traits to observe• Short generation time• Large number of offspring

What Traits did he Test?

• Flower color & position• Seed color and shape• Pod shape and color• Stem length

How do we determine an organisms genotype?

Monohybrid cross

Testcross: Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype

Mendel’s Experiment

Now it’s your turn!

Cross a homozygous Round Pea with a Wrinkle. Round is Dominant. What are the genotype and phenotype?

Heterozygous plant crossed with a heterozygous plant. What are the genotype and phenotype ratios?

1. Cross a heterozygous round pea with a wrinkle pea. What are the phenotype and genotype ratios?

2. Cross a heterozygous Purple pea with a homozygous purple. What are the phenotype and genotype ratios?

Punnet Square that crosses two different traits at the same time.

Example1. Cross a Yellow Tall homozygous pea with a Green Short Pea. Yellow and Tall are dominant

Dihybrid Cross

2. Cross a heterozygous Yellow Tall with a green heterozygous tall pea.

3. Cross a yellow tall heterozygous and a green short pea