Introduction to GeneticsChapter 11

Genetics The study of how traits are passed on

from parents to offspring.

Trait: Physical characteristic Ex: hair color, seed color, height

Gregor Mendel (1822-1884)

“Father of genetics” A monk from Austria Lived in a monastery where he was a

priest and a school teacher Experimented with pea plants in the

garden

Mendel studied 7 different pea plant traits Pea color, plant height, flower color, etc…

He wanted to know how the traits were passed

So he crossed (bred) two different plants to see what the offspring would look like

Mendel believed that the characteristics of pea plants are determined by the:

a) inheritance of units or factors from both parents

b) inheritance of units or factors from one parent

c) relative health of the parent plants at the time of pollination

Crossed a tall pea plant with a short pea plant

What did the offspring look like?

Where did the short trait go? Then he crossed the F1 offspring

What happened?

Short trait reappeared!

Mendel concluded:

Allele- form of a trait (written as letters) Ex: Tall pea plant = TT or Tt

A trait has two alleles 1 from mom, 1 from dad

Some traits are dominant and others are recessive.

(Why some of us look more like 1 parent than the other)

An allele is…

a) another word for a gene b) a homozygous genotype c) a heterozygous genotype d) one of several possible forms of a

gene

Dominant- Capital letter allele overpowers small letter, and the dominant trait is shown. Ex: Tt = Tall plant

Recessive- lowercase allele that is masked by dominant one, must have two recessive alleles to show the recessive trait. Ex: tt = short plant

Traits can be described in 2 ways:

Genotype- Genetic makeup (Tt, TT or Tt) Phenotype- Physical appearance (Tall or

short)

Homozygous- Two of the SAME alleles (both dominant OR both recessive)

TT or tt Heterozygous- One dominant allele and

one recessive allele Tt

Sex cells (sperm and eggs) can only carry 1 allele at a time for each trait.

If mom has a trait Gg Her eggs can only have a G or g If dad is GG, his sperm all have one G

Those sex cells mix to form the offspring’s genotype.

Those offspring can either be GG or Gg

When the genotype consists of a dominant and a recessive allele, the phenotype will be like _________________ allele.

a) the dominant b) the recessive c) neither

Stop Do activity

Problem: Cross a heterozygous tall pea plant with a heterozygous tall pea plant.

Step 1: What are the parents (P) genotypes?

Tt x Tt

Step 2: Set-up your Punnett square.

Step 3: Fill-in genotypes of offspring

Step 4: Make table to organize data

Step 5: Answer any questions asked of you about the results

Genotypic ratio: Phenotypic ratio: %chance having tall offspring: % chance having short offspring:

Freckles (F) is a dominant trait. Patty is homozygous for freckles while her hubby Harry is heterozygous for freckles.

What are the chances of their children having freckles ?

What is the phenotypic ratio?

Practice: Two dogs mate and have puppies. The

male dog is homozygous for black fur and the female is homozygous for yellow fur. Black is dominant and yellow is recessive.

Parents: ____ x ____How many puppies will have black fur?

What percent of the offspring have yellow fur?

Is it possible for these dogs tohave a puppy with yellow fur?

Why/Why not? Genotype # Phenotype