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Exploring Mendelian Genetics

Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

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Two-Factor Cross: F1 Generation Mendel crossed true-breeding plants that produced only round yellow peas (RRYY) with plants that produced wrinkled green peas (rryy). All F1 offspring from this cross had round yellow peas (RrYy) This cross produced hybrid plants for the next cross…

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Page 1: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Exploring Mendelian Genetics

Page 2: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Independent Assortment

• Does the segregation of one pair of alleles affect the segregation of another pair of alleles?– Mendel performed an experiment to follow two

different genes from generation to generation in a Two-Factor Cross = Dihybrid Cross

Page 3: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Two-Factor Cross: F1 Generation

• Mendel crossed true-breeding plants that produced only round yellow peas (RRYY) with plants that produced wrinkled green peas (rryy). All F1 offspring from this cross had round yellow peas (RrYy)

• This cross produced hybrid plants for the next cross…

Page 4: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Dihybrid CrossCross a Round, Yellow peas plant (RRYY) with

plants that produce Wrinkled, Green peas (rryy).

RRYY x rryy

R = round seed

r = wrinkled seed

Y = yellow seed

y = green seed

RY RY RY RY

ry

ry

ry

ry

RrYy RrYy RrYy RrYy

RrYy RrYy RrYy RrYy

RrYy RrYy RrYy RrYy

RrYy RrYy RrYy RrYy

All offspring produced have Round, Yellow peas.

Round, Yellow

Round, Yellow

Round, Yellow

Round, Yellow

Page 5: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Two-Factor Cross: F2 Generation

– Mendel crossed two F1 plants (RrYy) heterozygous for both seed shape and color

– Using a Punnett square, we can see that alleles for seed shape segregate independently of those for seed color = independent assortment.

Page 6: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Dihybrid CrossCross two plants that are heterozygous for round,

yellow seeds (RrYy).

RrYy x RrYy

R = round seed

r = wrinkled seed

Y = yellow seed

y = green seed

RY Ry rY ry

RY

Ry

rY

ry

RRYY RRYy RrYY RrYy

RRYy RRyy RrYy Rryy

RrYY RrYy rrYY rrYy

RrYy Rryy rrYy rryy

Phenotype Ratio -Round, Yellow

Round, Yellow

Round, Yellow

Round, Yellow

Round, Green

Round, Yellow

Round, Yellow

Round, Yellow

Round, Yellow

Round, Yellow

Round, Green

Round, Green

Wrinkled,Yellow

Wrinkled,Yellow

Wrinkled,Yellow

Wrinkled, Green

9 Round, Yellow

3 Round, Green

3 Wrinkled, Yellow

1 Wrinkled, Green

9 : 3 : 3 : 1 Ratio

Page 7: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Dihybrid Cross

Genotype Ratio –

1 RRYY : 2 RRYy :

2 RrYY : ….Ahhh!

Punnett square shows a 9:3:3:1 phenotypic ratio –

9 yellow round : 3 yellow wrinkled : 3 green round: 1 green wrinkled

Page 8: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Principle of Independent Assortment

• Genes for different traits can segregate independently during the formation of gametes.

Page 9: Exploring Mendelian Genetics. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? –Mendel

Summary of Mendel’s Principles

– Inheritance of biological information is determined by genes

– Some forms of a gene may be dominant or recessive

– Each adult organism has two copies of each gene – one from each parent

– Alleles for different genes usually segregate independently of one another