genetics i. heredity: how traits are passed from parents to offspring

GENETICSGENETICS

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

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

“Father of Genetics “• Austrian Monk• Worked with pea plants• 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•Self-fertilize•Easy traits to view, many offspring•Pea plants have DNA just like people

B. 7 traits Mendel Studied

A. Self FertilizationOffspring= Purebred

III. Fertilization

B. Cross Fertilization a. Offspring = Hybrid

CROSS POLLINATIONCROSS POLLINATION

HYBRID HYBRID

COCKAPOCOCKAPOOO

COCKER SPANIEL

+POODLE

HYBRIDHYBRIDPUG

+BEAGLE

PUGGLE

male lion and

a female tiger

Liger

Peas!

GENETIC GENETIC TERMINOLOGYTERMINOLOGY

•DominantDominant•RecessiveRecessive•HomozygousHomozygous•HeterozygouHeterozygouss

•GenotypeGenotype•PhenotypPhenotypee

•TraitTrait•AlleleAllele

A. Dominant allele: trait is always expressed if

present

- Written as capital letter

Ex: Tall = T

B. Recessive allele: only expressed if no

dominant allele is present (Dominant allele

masks this one)

- Written as the same letter but lower case

Ex: Short = t

IV. Genetic Terminology

C. Homozygous – two identical alleles for a gene - TT or tt or SS

D. Heterozygous – two different alleles for a

trait

- Tt or Ss

E. Genotype: the genes you get from your

parents

– You get two copies of every trait

– One from mom one from dad

– Ex: TT, Tt, tt

F. Phenotype: the physical

appearance, what you look

like

– Ex: “Tall” “short”

“yellow” or “green”

– Ex: TT, tt what is the

phenotype?

Trait = HeightTrait = Height

TALL SHORT alleles

G. Trait: variation of a particular character

H.H. Each trait is controlled by a gene that is in Each trait is controlled by a gene that is in two two contrasting formscontrasting forms

The different forms of a gene are called The different forms of a gene are called allelesalleles..

I. I. GeneGene: : section on section on DNA that DNA that codes for a codes for a protein protein (trait)(trait)

Reginald PunnettReginald Punnett

Punnett Square:chart to predict offspring Monohybrid: looks at ONE trait

In Starfish In Starfish being being redred is is dominant over dominant over being being pinkpink..1)1)What would What would PatrickPatrick’’s s phenotypephenotype be? be? 2)2)What would What would his his genotypegenotype be?be?

1) Because Patrick is pink… his phenotype is PINKPINK

2) And since pink is recessive – his genotype would be “r rr r”

RedRed is dominant over pinkpink

Suppose we had a HETEROZYGOUS redred starfish.

What would the genotype be?

R r

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 letter to useSelect a 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 & phenotypes Determine genotypes & phenotypes of offspring of offspring

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

In pea plants being tall is In pea plants being tall is dominant over being shortdominant over being short

Cross a heterozygous tall plant Cross a heterozygous tall plant with a homozygous tall plant.with a homozygous tall plant.

Heterozygous tall parent= T tHomozygous tall parent = T T

Tall= Tshort= t T

TT T T

TT T

t

t

T t

What is the genotype ratio?

50% TT50% TT50% tt50% tt

What is the phenotype

ratio?100% Tall100% Tall

Punnett Square2) Cross two heterozygous tall parents.

T

TT T T

Tt t

t

t

tt

What are the genotypes?

25% TT25% TT50% Tt50% Tt25% tt25% tt

What is the phenotype

ratio?75% Tall75% Tall25% short25% short

In sponges, In sponges, beingbeing blueblue is is dominant dominant over beingover being yellow.yellow.

Cross a Cross a heterozygous heterozygous blue sponge blue sponge with a yellow with a yellow one.one.

Heterozygous Heterozygous BlueBlue = Bb = BbRecessive Recessive YellowYellow= bb = bb

so we cross…so we cross…

Bb x bbBb x bb

B b

b

b b b

b bb

b

B

B

Genotype:50% Bb 50% bb

Phenotype:50% blue 50% yellow

Time for someTime for some

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

Red Red is is

dominant dominant over over BlueBlue

TTEESSTT CCRROOSSSS

Test Cross: mate an unknown genotype ( TT or Tt) with homozygous recessive (tt)

MENDELS LAWSMENDELS LAWS

1. Dominance & Recessiveness

2.Segregation3. Independent

Assortment

Dominance and Recessiveness

• One gene (dominant) can mask the other

(recessive)

Principle of Segregation

• Genes are separated or segregated during the formation of sex cells

• Only one gene from one parent

Independent Assortment

• Genes for traits separate independent of each other

• In Nemo- short fin can be inherited with a red body or an orange body due to separate chromosomes

PEDIGREEPEDIGREEmale female

Albino

polydactyly.