Download Warm Up - Ms. Chambers' Biology

Dihybrid Cross
&
Beyond Dominant and Recessive
Genetics
January 6, 2011
Warmup

In ginuea pigs, short hair (S) is dominant
to long hair (s). Two short-haired ginuea
pigs breed and one of the resulting
offspring is long-haired.
◦ Draw the punnett square to represent this
situation
◦ What are the genotypes of the parents?
Law of Independent
Assortment
Mendel wondered if alleles were “linked”
together.
 He knew yellow seeds (Y) were
dominant over green (y), and round seeds
(R) were dominant over wrinkled (r).
But…

◦ Are all yellow seeds were round?
◦ And all green seed were wrinkled?
Independent Assortment cont.

So he crossed them- Got the F1

RRYY (round yellow) x rryy (wrinkled green)
rryy
RRYY
ry
ry
ry
ry
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
RY
RrYy
RrYy
RrYy
RrYy
Independent Assortment cont
Then he did the F2
 He crossed the RrYy with
RrYy
 Since the seeds in the
generation no longer
linked being yellow and
round and green and
wrinkled. Mendel now
new that genes were
independent of each
other

Two laws from his observations

Law of
Segregation- when
you make your gametes
(sex cells), the copies of a
gene separate.

Ex. One of your sex cells may have
an allele for brown hair and
another gamete may have an allele
for red hair

Law of Independent
Assortment- genes for
different traits separate
independently of one
another
◦ Contributes to genetic
variations observed in plants
and animals
Beyond Dominant and Recessive

Some alleles are not dominant or
recessive and others are not controlled
by just one gene!
◦ Incomplete Dominance
◦ Codominance
◦ Multiple Alleles
◦ Polygenic traits
Incomplete Dominance



When one allele is not
dominant over another.
The heterozygous
genotype produces a mix
of the phenotypes
Red and white flower
producing PINK
Codominance

When both alleles contribute to the
phenotype
◦ Not mixed, but both present

Example: Red cows x White cows  red
and white spotted cows
Multiple Alleles
When a gene has more than 2 possible
alleles
 Although individuals can only have 2 there
are more in nature
 Example – ABO Human Blood Type
 Example– Fur color in rabbits

◦ Single gene, 4 alleles
Blood Types
Polygenic trait



When trait/phenotype is
controlled by the interaction
of more than 1 gene
Example: Skin color in
humans, high blood pressure
and height
Skin color- more than four
different genes that control
this trait
Polygenic traits- Skin Color
Homework

Finish green “Genetic Basics” worksheet
◦ # 15, 16, 17, 20
Fill in front side of 11-3 notes sheet (read
the section to complete)
 Quiz tomorrow!
