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Dihybrid Crosses. Genetics Continued. Law of Segregation. During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.

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Dihybrid crosses

Dihybrid Crosses

Genetics Continued


Law of segregation
Law of Segregation

  • During the formationofgametes(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.



Law of independent assortment
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 cross
Dihybrid Cross

  • A 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)


Question how many gametes will be produced for the following allele arrangements

Remember: 2n (n = # of heterozygotes)

1. RrYy

2. AaBbCCDd

3. MmNnOoPPQQRrssTtQq

Question:How many gametes will be produced for the following allele arrangements?


Answer
Answer

1. RrYy: 2n = 22 = 4 gametes

RY RyrYry

2. AaBbCCDd: 2n = 23 = 8 gametes

ABCD ABCdAbCDAbCd

aBCDaBCdabCDabCD

MmNnOoPPQQRrssTtQq:

2n= 26 = 64 gametes


Dihybrid cross1
Dihybrid Cross

  • Traits: Seed shape &Seed color

  • Alleles:(R)round, (r)wrinkled(Y)yellow, (y) green

  • Cross:

RrYy x RrYy

**use FOIL**

RY, Ry, rY, ry

RY, Ry, rY, ry

All possible gamete combinations


Dihybrid cross2

RY

Ry

rY

ry

RY

Ry

rY

ry

Dihybrid Cross


Dihybrid cross3

RY

Ry

rY

ry

RY

Ry

rY

ry

Dihybrid Cross

: 1

RRYY

RRYy

RrYY

RrYy

RRYy

RRyy

RrYy

Rryy

RrYY

RrYy

rrYY

rrYy

RrYy

Rryy

rrYy

rryy

9:3:3:1 phenotypic ratio


Dyhybrid analysis
Dyhybrid Analysis

  • Genotypes:

  • Genotypic Ratios:

  • Phenotypes:

    Round/Yellow : Round/green : wrinkled/Yellow : wrinkled/green

  • Phenotypic Ratios:

    9 : 3 : 3 : 1


Dihybrid cross4
Dihybrid Cross

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

9:3:3:1


Test cross

bC

b___

bc

Test Cross

  • A mating between an individual of unknown genotype and a homozygous recessive individual.

  • Example:bbC__ x bbcc

  • BB = brown eyes

  • Bb = brown eyes

  • bb = blue eyes

  • CC = curly hair

  • Cc = curly hair

  • cc = straight hair


Test cross1

bC

b___

C

bC

b___

c

bc

bbCc

bbCc

or

bc

bbCc

bbcc

Test Cross

  • Possible results:


Summary of mendel s laws

LAW

PARENT CROSS

OFFSPRING

DOMINANCE

TT x tttall x short

100% Tt tall

SEGREGATION

Tt x Tttall x tall

75% tall 25% short

INDEPENDENT ASSORTMENT

RrGg x RrGground & 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

Summary of Mendel’s laws


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