Dihybrid crosses
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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

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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.


Applying the law of segregation

Applying the Law of Segregation


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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