[PPT]Mendel's genetics - Mrs. Tosh's class -...

Mendelelian Genetics

copyright cmassengale

Gregor Mendel

(1822-1884)Responsible for the Laws governing

Inheritance of Traits

Gregor Johann MendelAustrian monkStudied the inheritance of traits in pea plantsDeveloped the laws of inheritanceMendel's work was not recognized until the turn of the 20th century copyright cmassengale

Gregor Johann MendelBetween 1856 and 1863, Mendel cultivated and tested some 28,000 pea plantsHe found that the plants' offspring retained traits of the parentsCalled the “Father of Genetics"

Site of Gregor Mendel’s experimental garden in the Czech Republic

Mendel stated that physical traits are inherited as “particles”Mendel did not know that the “particles” were actually Chromosomes & DNA

Particulate Inheritance

Genetic Terminology Trait - any characteristic that can be passed from parent to offspring

Heredity - passing of traits from parent to offspring

Genetics - study of heredity

Use Your Noodle!Answer the following in your science notebook.

What traits are found in your family?

copyright cmassengale 8

You have 2 minutes

Types of Genetic Crosses

Monohybrid cross - cross involving a single traite.g. flower color

Dihybrid cross - cross involving two traits e.g. flower color & plant height

Designer “Genes” Alleles - two forms of a gene

(dominant & recessive) Dominant - stronger of two

genes expressed in the hybrid; represented by a capital letter (R)

Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r) copyright cmassengale

More Terminology Genotype - gene combination for a trait (e.g. RR, Rr, rr)

Phenotype - the physical feature resulting from a genotype (e.g. red, white)

Genotype & Phenotype in Flowers

Genotype of alleles:R = red flowerr = yellow flowerAll genes occur in pairs, so 2 alleles affect a characteristicPossible combinations are:Genotypes RR Rr rrPhenotypesRED RED YELLOW

Use Your Noodle!Answer the following in

your science notebook.

Determine which allele is dominate and recessive?

RrGGHhff

You have 2 minutes

Genotypes Homozygous genotype - gene

combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure

Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid copyright cmassengale

Use Your Noodle!Answer the following in

your science notebook.

Determine which allele is Homozygous or Heterozygous?

RrGGHhff

You have 2 minutes

Genes and Environment Determine Characteristics

Mendel’s Pea Plant

Experiments

Why peas, Pisum sativum?

Can be grown in a small area Produce lots of offspring Produce pure plants when allowed to self-pollinate several generations Can be artificially cross-pollinated copyright cmassengale

Mendel’s Experimental

MethodsMendel hand-pollinated flowers using a paintbrush

He could snip the stamens to prevent self-pollinationCovered each flower with a cloth bag

He traced traits through the several generations

How Mendel BeganMendel produced pure strains by allowing the plants to self-pollinate for several generations copyright cmassengale

Eight Pea Plant TraitsSeed shape --- Round (R) or Wrinkled

(r)Seed Color ---- Yellow (Y) or Green

(y)Pod Shape --- Smooth (S) or wrinkled

(s)Pod Color --- Green (G) or Yellow (g)Seed Coat Color ---Gray (G) or White

(g)Flower position---Axial (A) or

Terminal (a)Plant Height --- Tall (T) or Short (t)Flower color --- Purple (P) or white

22copyright cmassengale

Mendel’s Experimental Results

Following the Generations

Cross 2 Pure

PlantsTT x tt

Results in all

HybridsTt

Cross 2 Hybrids

get3 Tall & 1

ShortTT, Tt, tt

Punnett SquareUsed to help solve genetics problems

Monohybrid Crosses

Trait: Seed ShapeAlleles: R – Round r – WrinkledCross: Round seeds x Wrinkled

seedsRR x rr

P1 Monohybrid Cross

Genotype: RrPhenotype: RoundGenotypicRatio: All alikePhenotypicRatio: All alike

P1 Monohybrid Cross Review

Homozygous dominant x Homozygous recessive

Offspring all Heterozygous (hybrids)

Offspring called F1 generation Genotypic & Phenotypic ratio

is ALL ALIKE

Trait: Seed ShapeAlleles: R – Round r – WrinkledCross: Round seeds x Round seeds

Rr x Rr

F1 Monohybrid Cross

Genotype: RR, Rr, rrPhenotype: Round & wrinkledG.Ratio: 1:2:1P.Ratio: 3:1

F1 Monohybrid Cross Review

Heterozygous x heterozygous Offspring:

25% Homozygous dominant RR50% Heterozygous Rr25% Homozygous Recessive rr

Offspring called F2 generation Genotypic ratio is 1:2:1 Phenotypic Ratio is 3:1

What Do the Peas Look Like?

…And Now the Test CrossMendel then crossed a pure &

a hybrid from his F2 generation

This is known as an F2 or test cross

There are two possible testcrosses:Homozygous dominant x HybridHomozygous recessive x Hybrid

Trait: Seed ShapeAlleles: R – Round r – WrinkledCross: Round seeds x Round seeds

RR x Rr

F2 Monohybrid Cross (1st)

Genotype: RR, RrPhenotype: RoundGenotypicRatio: 1:1PhenotypicRatio: All alikecopyright cmassengale

Trait: Seed ShapeAlleles: R – Round r – WrinkledCross: Wrinkled seeds x Round seeds

rr x Rr

F2 Monohybrid Cross (2nd)

Genotype: Rr, rrPhenotype: Round & WrinkledG. Ratio: 1:1P.Ratio: 1:1

F2 Monohybrid Cross Review

Homozygous x heterozygous(hybrid)

Offspring:50% Homozygous RR or rr50% Heterozygous Rr

Phenotypic Ratio is 1:1 Called Test Cross because the

offspring have SAME genotype as parents

Practice Your Crosses

Work the P1, F1, and both F2 Crosses for each of the other

Seven Pea Plant Traits

Mendel’s Laws

Results of Monohybrid Crosses

Inheritable factors or genes are responsible for all heritable characteristics

Phenotype is based on Genotype

Each trait is based on two genes, one from the mother and the other from the father

True-breeding individuals are homozygous ( both alleles) are the samecopyright cmassengale

Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation.All the offspring will be heterozygous and express only the dominant trait.RR x rr yields all Rr (round seeds)

Law of Dominance

Law of SegregationDuring the formation of

gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.

Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

Applying the Law of Segregation

Law of Independent Assortment

Alleles for different traits are distributed to sex cells (& offspring) independently of one another.

This law can be illustrated using dihybrid crosses.

Dihybrid CrossA breeding experiment that

tracks the inheritance of two traits.

Mendel’s “Law of Independent Assortment”

a. Each pair of alleles segregates independently during gamete formation

b. Formula: 2n (n = # of heterozygotes)copyright cmassengale

Question:How many gametes will be

produced for the following allele arrangements?

Remember: 2n (n = # of heterozygotes)

1. RrYy

2. AaBbCCDd

3. MmNnOoPPQQRrssTtQqcopyright cmassengale

Answer:1. RrYy: 2n = 22 = 4 gametes

RY Ry rY ry

2. AaBbCCDd: 2n = 23 = 8 gametesABCD ABCd AbCD AbCdaBCD aBCd abCD abCD

3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes

Dihybrid CrossTraits: Seed shape & Seed colorAlleles: R round

r wrinkled Y yellow y green

RrYy x RrYy

RY Ry rY ry RY Ry rY ry

All possible gamete combinationscopyright cmassengale

Dihybrid CrossRY Ry rY ry

Dihybrid Cross

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 19:3:3:1 phenotypic ratio

RY Ry rY ry

Dihybrid Cross

Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1

9:3:3:1

Test CrossA mating between an individual of

unknown genotype and a homozygous recessive individual.

Example: bbC__ x bbcc

BB = brown eyesBb = brown eyesbb = blue eyes

CC = curly hairCc = curly haircc = straight hair

bC b___

Test CrossPossible results:

bC b___

bc bbCc bbCc

C bC b___

bc bbCc bbccor

Summary of Mendel’s laws

LAW PARENT CROSS OFFSPRING

DOMINANCE TT x tt tall x short

100% Tt tall

SEGREGATION Tt x Tt tall x tall

75% tall 25% short

INDEPENDENT ASSORTMENT

RrGg x RrGg round & green x round & green

9/16 round seeds & green pods

3/16 round seeds & yellow pods

3/16 wrinkled seeds & green pods

1/16 wrinkled seeds & yellow pods

Incomplete Dominanceand

Codominance

Incomplete Dominance

F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties.

Example: snapdragons (flower)red (RR) x white (rr)

RR = red flowerrr = white flower

All Rr = pink(heterozygous pink)

produces theF1 generation

CodominanceTwo alleles are expressed

(multiple alleles) in heterozygous individuals.

Example: blood type

1. type A = IAIA or IAi2. type B = IBIB or IBi3. type AB= IAIB

4. type O = iicopyright cmassengale

Codominance ProblemExample:homozygous male Type B

(IBIB)x

heterozygous female Type A (IAi)

IAIB IBi

1/2 = IAIB

1/2 = IBi IB

Another Codominance Problem

• Example: male Type O (ii) x female type AB (IAIB)

IAi IBi

1/2 = IAi1/2 = IBi

CodominanceQuestion:

If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents?

boy - type O (ii) X girl - type AB (IAIB)

CodominanceAnswer:

Parents:genotypes = IAi and IBiphenotypes = A and B

Sex-linked Traits

Traits (genes) located on the sex chromosomes

Sex chromosomes are X and YXX genotype for femalesXY genotype for malesMany sex-linked traits carried

on X chromosome

Sex-linked Traits

Sex Chromosomes

XX chromosome - female Xy chromosome - male

fruit flyeye color

Example: Eye color in fruit flies

Sex-linked Trait Problem

Example: Eye color in fruit flies (red-eyed male) x (white-eyed

female) XRY x XrXr

Remember: the Y chromosome in males does not carry traits.

RR = red eyedRr = red eyedrr = white eyedXY = maleXX = female

Sex-linked Trait Solution:

50% red eyed female

50% white eyed male

Female Carriers

Genetic Practice Problems

Breed the P1 generation

tall (TT) x dwarf (tt) pea plants

Solution:

Tt All Tt = tall(heterozygous tall)

produces theF1 generation

tall (TT) vs. dwarf (tt) pea plants

Breed the F1 generation

tall (Tt) vs. tall (Tt) pea plants

Solution:

T tproduces theF2 generation1/4 (25%) = TT1/2 (50%) = Tt1/4 (25%) = tt1:2:1 genotype 3:1 phenotype

tall (Tt) x tall (Tt) pea plants

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