GENETICS Heredity – how traits are passed from parents to offspring

GENETICSGENETICS

Heredity – how traits are passed from parents to offspring

GREGOR MENDELGREGOR MENDEL (1822- (1822- 1884)1884)

- Father of Genetics - Austrian Monk from 1822- 1884 - Job was to take care of the

garden- Worked with pea plants ( lots of pea soup)

- Noticed that traits were passed from parent peas to their offspring

- Before him people believed in the blending hypothesis

Why are pea plants good to study?

- Reproduce quickly, easy traits to view, many offspring - Pea plants have DNA just like we do

Self FertilizationOffspring= Purebred

Sperm and egg from the same plant produce offspring

Cross Fertilization Offspring = Hybrid

process by which sperm from one flower's pollen fertilizes the eggs in a flower of a different

plant, heterozygous

CROSS POLLINATIONCROSS POLLINATION

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 if present

- 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 and Recessive Alleles

• Homozygous - the same alleles for a gene

– TT, tt

• Heterozygous - having different alleles for a gene

– Tt

• Genotype- the genes you get from your parents– Two letters represent the two alleles– One from mom one from dad – TT, Tt, tt

• Phenotype- the physical trait, what you look like – Tall short, yellow or green – TT, tt what is the phenotype?

Trait = CharacteristicTrait = CharacteristicEx: HeightEx: Height

TALL SHORT alleles

Flower Color Trait

• Gene- unit of inherited information in DNA • Allele- alternative form of a gene (white purple)

Reginald PunnettReginald Punnett

Introduction to Monohybrid Crosses

• Punnett Square- chart to predict offspring

• Monohybrid- looks 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 or segregated during

the formation of sex cells. • Only one gene from one parent.

3. Independent Assortment

• genes for traits separate independent of 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- mate an unknown genotype ( TT or Tt) with homozygous recessive (tt)

PEDIGREEPEDIGREEmale female