Genetics

Ms. Tetrev

• Do all dogs look alike? What types of features indicate a particular breed?

• Can you tell individuals within a particular breed apart?

• What does this tell you about the inheritance of these features?

Genetics

• The science of heredity, began with Mendel, who is regarded as the father of genetics.

• Mendel performed cross-pollination in pea plants.

• Mendel followed various traits in the pea plants he bred.

• The passing of traits from generation to the next generation is called INHERITANCE or Heredity.

• True-breeding means it consistently produces offspring with only one form of a trait.– Why is it important that Mendel’s Experiments

used a true-breeding plant?

• Mendel performed cross-pollination by transferring male gametes from the flower of a true-breeding green-seed plant to the female organ of a flower from a true-breeding yellow-seed plant.

• The parent generation is also known as the P generation

• The offspring of this P cross are called the first filial (F1) generation.

• The second filial (F2) generation is the offspring from the F1 cross.

• Why are the seeds in the F1 generation all yellow?

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Mendel studied seven different traits.

• Seed shapeSeed shape --- Round --- Round (R)(R) or Wrinkled or Wrinkled (r)(r)• Seed ColorSeed Color ---- Yellow ---- Yellow (Y)(Y) or Green or Green ((yy))• Pod ShapePod Shape --- Smooth --- Smooth (S)(S) or wrinkled or wrinkled ((ss))• Pod ColorPod Color --- Green --- Green (G)(G) or Yellow or Yellow (g)(g)• Seed Coat ColorSeed Coat Color ---Gray ---Gray (G)(G) or White or White (g)(g)• Flower positionFlower position---Axial ---Axial (A)(A) or Terminal or Terminal (a)(a)• Plant HeightPlant Height --- Tall --- Tall (T)(T) or Short or Short (t)(t)• Flower color Flower color --- --- Purple Purple (P)(P) or white or white ((pp))

• An Allele is an alternative form of a single gene passed from generation to generation.– Example: The gene for seed shape in pea plants

exists in two forms, one form or allele for round seed shape (R) and the other for wrinkled seed shape (r).

• Dominant -The stronger allele, represented by a capital letter (R)

• Recessive- the weaker allele that is masked, represented by a lowercase letter (r)

• An organism with two of the same alleles for a particular trait is homozygous. Gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure pure

• An organism with two different alleles for a particular trait is heterozygous. Gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid

• An organism’s allele pairs are called its genotype. The gene combination for a traitgene combination for a trait What genes, letters, the organism has (TT, Tt, tt)

• The observable characteristic or outward expression of an allele pair is called the phenotype. The physical feature resulting The physical feature resulting from a genotype from a genotype What it looks like!

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Following the GenerationsFollowing the Generations

Cross 2 Cross 2 Pure Pure PlantsPlantsTT x ttTT x tt

Results Results in all in all HybridsHybridsTtTt

Cross 2 Cross 2 HybridsHybridsgetget3 Tall & 1 3 Tall & 1 ShortShortTT, Tt, ttTT, Tt, tt

Mendel’s Law of Segregation• Two alleles for each trait separate during

meiosis.• During fertilization, two alleles for that trait

unite.• Heterozygous organisms are called hybrids.

Punnett Squares

• Predict the possible offspring of a cross between two known genotypes

Law of SegregationLaw of Segregation

• During the During the formation of gametesformation of gametes (eggs or (eggs or sperm), the sperm), the two allelestwo alleles responsible for a responsible for a trait trait separateseparate from each other. from each other.

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

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Applying the Law of SegregationApplying the Law of Segregation

copyright cmassengale

Monohybrid

• A cross that involves hybrids for a single trait is called a monohybrid cross.

• Trait: Seed ShapeTrait: Seed Shape• Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled• Cross: Cross: RoundRound seedsseeds xx Wrinkled Wrinkled seedsseeds• RRRR xx rr rr

PP11 Monohybrid Cross Monohybrid Cross

R

R

rr

Rr

RrRr

Rr

Genotype:Genotype: RrRr

PhenotypePhenotype: RoundRound

GenotypicGenotypicRatio:Ratio: All alikeAll alike

PhenotypicPhenotypicRatio:Ratio: All alike All alike

PP11 Monohybrid Cross Review Monohybrid Cross Review

Homozygous dominant x Homozygous Homozygous dominant x Homozygous recessiverecessive

OffspringOffspring allall HeterozygousHeterozygous (hybrids)(hybrids) Offspring calledOffspring called FF11 generation generation Genotypic & Phenotypic ratio isGenotypic & Phenotypic ratio is ALL ALIKEALL ALIKE

• Trait: Seed ShapeTrait: Seed Shape• Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled• Cross: Cross: RoundRound seeds seeds xx Round Round seedsseeds• RrRr xx Rr Rr

FF11 Monohybrid Cross Monohybrid Cross

R

r

rR

RR

rrRr

Rr

Genotype:Genotype: RR, Rr, RR, Rr, rrrr

PhenotypePhenotype: Round Round && wrinkled wrinkled

G.Ratio:G.Ratio: 1:2:11:2:1

P.Ratio:P.Ratio: 3:1 3:1

FF11 Monohybrid Cross Review Monohybrid Cross Review

Heterozygous x heterozygousHeterozygous x heterozygous Offspring:Offspring:

25% Homozygous dominant25% Homozygous dominant RRRR50% Heterozygous50% Heterozygous RrRr25% Homozygous Recessive25% Homozygous Recessive rrrr

Offspring calledOffspring called FF22 generation generation Genotypic ratio isGenotypic ratio is 1:2:11:2:1 Phenotypic RatioPhenotypic Ratio is 3:1 is 3:1

Law of Independent assortment

• Random distribution of alleles occurs during gamete formation

• Genes on separate chromosomes sort independently during meiosis.

• Each allele combination is equally likely to occur

Dihybrid Cross

• The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross.

• Dihybrids are heterozygous for both traits.

Dihybrid CrossDihybrid Cross• A breeding experiment that tracks the A breeding experiment that tracks the

inheritance of two traitsinheritance of two traits..

• Mendel’s Mendel’s “Law of Independent “Law of Independent Assortment”Assortment”

• a. Each pair of alleles segregates a. Each pair of alleles segregates independentlyindependently during gamete formationduring gamete formation

• b. Formula: 2b. Formula: 2nn (n = # of heterozygotes) (n = # of heterozygotes)

Dihybrid CrossDihybrid Cross• Traits: Seed shape & Seed colorTraits: Seed shape & Seed color• Alleles:Alleles: R round

r wrinkled Y yellow y green

•

RrYy x RrYy

RY Ry rY ryRY Ry rY ry RY Ry rY ryRY Ry rY ry

All possible gamete combinationsAll possible gamete combinations

Dihybrid CrossDihybrid Cross

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Dihybrid CrossDihybrid Cross

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 1

9:3:3:1 phenotypic ratio

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

Dihybrid CrossDihybrid Cross

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

9:3:3:1