Warm-Up # 7 3/12/13• In humans, brown eyes (B) are dominant

over blue (b)*. A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed.

1) What is the man’s genotype? 2) The woman’s genotype?3) Draw the Punnett square that illustrates

this marriage. 4) What are the genotypes of the children?

Bb bb

Bb bb

B b

b

b

Man’s genotype: Bb (Heterozygous Dominant)

Woman’s genotype: bb (Homozygous recessive)

Kid’s genotypes:

2-Bb (Heterozygous Dominant)

1-bb (Homozygous recessive)

Independent Assortment, Dihybrid Crosses, and Beyond

Dominant/ Recessive

Ch 11-3

What’s This???

• Essential Question– How are

independent assortment and dihybrids related?

• Objectives – What is the principle

of independent assortment?

– What inheritance patterns exist aside from simple dominance?

– Explain how Mendel’s principles apply to all organisms?

Independent Assortment Review

• Genes for different traits separate independently from one another when gametes are formed.

• In order to come to the conclusion of independent assortment, Mendel did an experiment…

Independent Assortment & 2-Factor Crosses

• Mendel followed 2 different genes.• It is called a two-factor (Dihybrid)

cross.– Type of Punnett Square – 16 squares– Results: 9:3:3:1 (ratio)

Dihybrid Crosses Example

• Followed two traits • Gene for seed color and texture

– Seed color………….Y=yellow, y=green– Seed texture ……… R=round,

r=wrinkled

• They were dihybrid, meaning both traits were hybrids (heterozygous)

• Let’s try one………

Dihybrid Cross – RrYy x RrYy

RY Ry rY ry

RY

Ry

rY

ry

RRYY RRYy RrYY RrYy

RRYy RRyy RrYy Rryy

RrYY RrYy rrYY rrYy

RrYy Rryy rrYy rryy

9 round-yellow:

F1 Gametes

3 round-green: 3 wrinkled-yellow: 1 wrinkled-green

Mendel’s Results

• Out of 556 seeds, he found – 315 were round and yellow– 108 were round and green– 101 were wrinkled and yellow– 32 were wrinkled and green

• Guess what ratio this is???

– 315: 108: 101: 32 ≈ _______9:3:3:1

Mendel’s Conclusion

• He concluded: Genes that separate independently DO NOT influence each other’s inheritance. (independent assortment)

• Helps account for the many genetic variations

When Heredity Follows Different Rules

• Some alleles are neither dominant nor recessive.

• Many are controlled by multiple alleles or multiple genes.

Incomplete Dominance

• Neither allele is completely dominant.

• The heterozygous phenotype is a blend of the two homozygous phenotypes.

• Ex: Red flower x white flower = pink flower.

Codominance

• Both alleles are ‘dominant’.• Both colors show at the same time.• Ex: black chicken x white chicken

= black AND white chicken (NOT GRAY).

Multiple Alleles• Many genes

have more than 2 alleles.

• The organism still gets ONLY 2 alleles for the trait.

• Ex: rabbit color and human blood type.

Human Blood TypesAlleles = IA, IB, and iBlood types (phenotypes) = A, B, AB, O

Phenotype (blood type)

Genotype

A IAIA or IAi

B IBIB or IBi

AB IAIB

O ii

Let’s Practice!

• On the back of your notes, complete the following crosses and list offspring possibilities:

1) Mother has AB blood and Father has B blood (recessive)

2) Mother has AB blood and Father has B blood dominant.

1)

2)

IA IB

IB

i

MOM

DAD

IA IB IB IB

IA i iIB

Outcome:

1 child with AB blood (IAIB)

2 Children with B blood(IBIB, IBi)

1 Child with A blood (IAi)

IA IB MOM

IB

IB

IB IB IB

IB IB IB

IA

IA

DAD

Outcome:

2 children with AB blood (IAIB)

2 children with B blood (IBIB)

Multiple Alleles in Dogs • Labrador Retriever

Genetics• Black is dominant to

chocolate B or b• Yellow is recessive

epistatic (when present, it blocks the expression of the black and chocolate alleles) E or e

BBEE BbEE BBEe BbEe

bbEEbbEe

BBeeBbeebbee

Albino Rabbitcc

Chinchilla Rabbitcchc, cchcch, or cchch

Full Color RabbitCC, Ccch, Cch, or Cc

Himalayan Rabbitchc or chch

Polygenic Traits

• Poly - many• Genic - gene• Traits controlled by 2 or more

genes.• Wide variety of phenotypes• Ex: human skin color (controlled by

>4 genes) and human eye color.

Environmental Influence

• Characteristics of an organism are determined by its genes AND its environment.

• Ex: you may have the genes to be 6’ tall, but if you don’t have proper nutrition, you won’t be 6’!

Let’s Practice!• On back of

notes, complete the following cross:

• F1 guinea pigs: male BbSs x female BbSs

• B=black fur, b=brown fur

S=short fur, s=long fur

Dihybird Cross Practice

• You will work with one parnter to complete the Dihybrid cross worksheet

• Anything not finished today will need to be finished for homework tonight