Genetics – Life’s Blueprint

Genetics – Life’s Blueprint

Before MendelBefore Mendel

The Theory of Blended Traits

Why wasn’t it a good theory?

Mendel and his PeasMendel and his Peas

1822 - 18841822 - 1884

The Seven Traits• Flower Color

purple vs white• Flower placement

axial vs terminal• Seed Color

yellow vs green• Seed Shape

round vs wrinkled• Pod Shape

plump vs wavy• Pod Color

green vs yellow• Stem Length

tall vs dwarf

Mendel First CrossMendel First CrossTrait Studied – Flower ColorGeneratio

nPhenotype Phenotype

Parents

F1

F2

Ratio 3 1

Mendel’s First Law – the Law of SegregationMendel’s First Law –

the Law of Segregation

Observation - There is more than one version of a trait. (Each version is called an allele)

Law – • Each organism inherits two alleles, one from

each parent• One allele “dominates” when present • The other allele “recedes” when the

dominant allele is present

Mendel First CrossMendel First CrossTrait Studied – Flower ColorGeneratio

nPhenotype Phenotype

Parents

F1

F2

Ratio 3 1

Punnet SquaresPunnet SquaresTrait Studied – Flower ColorGeneratio

nPhenotype Phenotype

Parents PP pp

F1 Pp

F2

Ratio

PPPp

3

pp

1

Punnet SquaresPunnet Squares

Trait Studied – Flower Color in F1 Cross

Pp x Pp P p

P PP Pp

p Pp pp

Punnet Squares – Test Cross

Punnet Squares – Test Cross

Trait Studied – Flower Color

P? x pp p p

P Pp Pp

? ?p ?p

Simple Mendelian Problems

Simple Mendelian Problems

1. Given the parents’ genotypes what are the offsprings’ possible phenotypes and ratios?

2. Given the parents’ phenotypes and the offsprings phenotypic ratios, what are the parents’ genotypes?

Mendel’s Second Law – the Law of Independent

Assortment

Mendel’s Second Law – the Law of Independent

Assortment

Observation – When two traits are followed, they don’t always stay together

Law – Each pair of alleles segregates independently

ofthe other pairs of alleles during gamete

formation

Punnet Squares – Two Traits

Punnet Squares – Two Traits

Parents

Green Smooth vs Yellow Wrinkled

F1

Green Smooth only

F2 Green Smooth Green Wrinkled Yellow Smooth and Yellow Wrinkled

Punnet Squares – Two Traits

Punnet Squares – Two Traits

Parent Gametes and F1 Genotypes

Parents Gametes GS GS

gs GgSs GgSs

gs GgSs GgSs

Punnet Squares – Two Traits

Punnet Squares – Two Traits

F1 Gametes and F2Traits– Seed Color and Texture

GgSs x GgSs GS Gs gS gs

GS GGSS GGSs GgSS GgSs

Gs GGSs GGss GgSs Ggss

gS GgSS GgSs ggSS ggsS

gs GgSs Ggss ggSs ggssPhenotype Ratio

Green Smooth 9/16

Green Wrinkled

3/16

Yellow Smooth 3/16

Yellow Wrinkled

1/16

Phenotypic ProbabilitiesPhenotypic ProbabilitiesF1 Gametes and F2Traits– Seed Color and

Texture

GgSs x GgSs GS Gs gS gs

GS GGSS GGSs GgSS GgSs

Gs GGSs GGss GgSs Ggss

gS GgSS GgSs ggSS ggsS

gs GgSs Ggss ggSs ggssPhenotype Ratio

Green Smooth

9/16 = 56%

Green Wrinkled

3/16 = 19%

Yellow Smooth

3/16 = 19%

Yellow Wrinkled

1/16 = 6%

Multiple Trait ProblemsMultiple Trait Problems

1. Given the parents’ genotypes what are the offsprings’ possible phenotypes and ratios?

2. Given the parents’ phenotypes and the offsprings phenotypic ratios, what are the parents’ genotypes?