GENETICSGENETICS

I. Heredity:How traits are passed from parents to offspring

II. GREGOR MENDEL (1822- 1884)II. GREGOR MENDEL (1822- 1884)

- “Father of Genetics” - Austrian Monk from 1822-

1884 - Job was to take care of the

garden- worked with peas - Noticed that traits were

passed from parent peas to their offspring

- Before him people believed in the blending hypothesis

A. Why are pea plants good to study? - Reproduce quickly, easy traits to view, many offspring

- Pea plants have DNA just like we do

A. Self Fertilization: Sperm and egg from the same plant produce offspring

Offspring= Purebred

a. Offspring = Hybrid heterozygous

B. Cross Pollination process by which sperm from one flower's pollen fertilizes different flower’s eggs

HYBRID HYBRID

COCKAPOCOCKAPOOO

COCKER SPANIEL

+POODLE

HYBRIDHYBRIDPUG

+BEAGLE

PUGGLE

HYBRIDHYBRID

DOG DOG ANDAND WOLFWOLF

male lion and

a female tiger

Liger

Peas!

GENETIC GENETIC TERMINOLOGYTERMINOLOGY

•DominantDominant•RecessiveRecessive•HomozygousHomozygous•HeterozygouHeterozygouss

•GenotypeGenotype•PhenotypPhenotypee

•TraitTrait•AlleleAllele

• Dominant allele- trait is always expressed

- Written as capital letter

- Ex. Tall= T

• Recessive allele- only expressed if no dominant allele is present (Dominant allele masks this one)

- For a particular trait written as the same letter but lower case

- Ex. Short= t

Dominant & Recessive Alleles

• Homozygous – identical alleles for a trait

– TT, tt

• Heterozygous – not identical alleles for a trait

– Tt

• Genotype- the genes you get from parents– Two letters represent the two chromosomes– One from each parents– Ex: TT, Tt, tt

• Phenotype- the physical trait, what you look like – “Tall”, “short”, “yellow”, or “green”

Trait = A genetic characteristicTrait = A genetic characteristic Ex: Height Ex: Height

TALL alleles SHORT

Flower Color Trait

Allele- alternative forms of a gene

Reginald PunnettReginald Punnett

Introduction to Monohybrid Crosses

• Punnett Square- chart to predict offspring

• Monohybrid- looks at ONE trait• Ex: Looking at just plant color, or just

height, or just seed color

In Starfish In Starfish being being redred is is

dominant over dominant over being being pinkpink.. What would What would

PatrickPatrick’’s s phenotypephenotype be? What be? What would his would his

genotypegenotype be? be?

Because Patrick is pink… his

phenotype is PINKPINK

And since pink is

recessive – his

genotype

would be “rrrr ”

RedRed is dominant over

pinkpinkSuppose we

had a HETEROZYGO

US redred starfish what

would the genotype be?

Rr

LetLet’’s do some… s do some… MONOHYBRID MONOHYBRID

CROSSES!CROSSES!

MonohybridMonohybrid means means we are only using we are only using

ONE TRAITONE TRAIT

STEP by STEPSTEP by STEP1.1. Select a Select a ““goodgood”” letter to use letter to use

2.2. Write down your Write down your ““givensgivens””

3.3. Determine parents and recordDetermine parents and record

4.4. Set up Punnett SquareSet up Punnett Square

5.5. Determine genotypes & Determine genotypes & phenotypes of offspring phenotypes of offspring

(use percentages or fractions)(use percentages or fractions)

In pea plants, In pea plants, Tall is dominant to shortTall is dominant to short

Cross a Cross a Heterozygous Tall plant Heterozygous Tall plant

with a with a Homozygous Tall plantHomozygous Tall plant

Tt x TT

Geno = 50% T T50% T t

Pheno =100% Tall

A

A

A

T

t

T T

T T T T

T t T t

In sponges, In sponges, beingbeing blueblue

is dominant is dominant over beingover being

yellow.yellow.Cross a Cross a

heterozygouheterozygous blue s blue

sponge with sponge with a yellow a yellow

one.one.

HeterozygoHeterozygous us BlueBlue = = BbBbRecessive Recessive YellowYellow = bb = bb so we so we cross…cross…

Bb x Bb x bbbb

Time for someTime for some

LOONEY Monohybrid Monohybrid Crosses onCrosses on your own! your own!

MENDELS LAWSMENDELS LAWS

1. Dominance & Recessiveness

2.Segregation3. Independent

Assortment

1. Dominance & Recessiveness

one gene (dominant) can mask the other (recessive)

2. Segregation• genes are separated during the formation of sex

cells. • Offspring inherit only one gene from each parent.

3. Independent Assortment

• genes for different traits inherited independently from each other

• In dihybrid crosses, gives you several possibilities– Ex: In Nemo- short fin can be inherited with a

red body or an orange body- separate chromosomes

Independent Assortment

TTEESSTT CCRROOSSSS

Test Cross:In a test cross, always cross the unknown genotype (TT or Tt) with homozygous recessive (tt).

Using the context of what the results were, will determine which genotype is the unknown.

PEDIGREEPEDIGREEmale female