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