Download Intermediate Patterns of inheritance

Genetics
Incomplete and Co-dominant inheritance patterns
Work with a
partner and
answer the
following:
Do you think twins could be
born of two different color
skins? If yes, how do you think
this can happen and if no, why
could this not happen?
·
Intermediate
Patterns of
Inheritance
Review:
Complete
Dominance
Mendel experiments showed the
following:
● One homozygous recessive (rr
and white color) X homozygous
dominant (RR and purple
color) = All off offspring
Heterozygous (Rr and Purple
color)
● Then, cross two of the F1
offspring (Heterozygous) (Rr
and Purple color). All F2
offspring show 3:1 phenotypic
ratio or 1:2:1 genotypic ratio
● Well, this is not always the
case….
Incomplete
dominance
● A form of inheritance in
which the heterozygous
alleles are both expressed,
resulting in a combined
phenotype.
● Think: Blending
● Example: Flowers
Recap
● We have examined complete dominance, in which one
allele is clearly dominant over the other
● incomplete dominance, in which neither allele
dominates over the other.
● In a third type of dominance, codominance, both
alleles are expressed in the phenotype of individuals
that have heterozygous alleles.
Codominance
In a certain fish, blue scales and red scales are
codominant. When a fish has the genotype B R, it has
a patchwork of blue and red scales. What happens if
you breed this fish with a fish that only has Blue Scales.
Step 1: Determine the genotypes of the parents
Step 2: Set up the box!
B R = patchwork fish
B B = blue fish
Step 3: Count the number of each phenotype:
R R = red fish
What
happens
when you
cross two
patchwork
fish?
1/2 will by patchwork, 1/2 will be blue
Solve?
1: BB
2: BR
1: RR
Multiple Alleles- Three or more alleles for a
particular gene
● Great Example: Human Blood Type
● 3 Alleles for the 1 gene that determines your blood
type (Remember you only have 2 of the 3 alleles- one
from each parent)
● Four possible phenotypes
One more example- Work with a partner and
solve the following problem:
Genotype: Phenotype
Blood type A: IA IA
Blood type B: IBIB
Blood type AB: IAIB
What is the probability of having a child with a different genotype, if mother
has type A blood type and father has type B blood type? Be sure to include
genotypes and phenotypes in your work:
● Complete an F1 generation cross, show your work and then complete an
F2 cross. Show your work
Answer: genotype and phenotype ratio both 1:2:1
● red blood cells have special
markers called antigens
● Type AB has both antigens,
Color Blindness- How is this inherited?
● Work with a partner and think of possible two reasons of how
a person could inherit color blindness?
● List two challenges an individual could face if color blind.
● Gender determined
from Dad, because mom
will always supply an X
Sex-linked Traits “Gender”
50% chance of being male or 50% chance
of being female
What does it mean to have a
sex-linked trait?
If the gene is recessive, then males only need one such
recessive gene to have a sex-linked trait rather than
the customary two recessive genes for traits that are
not sex-linked. This is why males exhibit some traits
more frequently than females.
So...Henry the
VIII
Decapitated Anne Boleyn
because no male heirs….
Sex-Linked Example:
Hemophilia
• genetic disorder, impair
the body's ability to
control blood clotting
• recessive, What does
that mean?
.
Polygenic Traits
● Trait controlled by more than one gene
o The result is the perception of continuous gradation in the
expression of these traits.
o specialized skin cells produce the pigment, melanin
● Height, skin color and even eye color (recently discovered)
● Example: Skin color
o A genotype of AABBCC would express dark skin
o A genotype of aabbcc would express light skin
Test Cross
● Test crosses involve breeding the individual in question
with another individual that expresses a recessive
version of the same trait.
● Test cross = the cross of an organism with an unknown
dominant genotype with an organism that is
homozygous recessive for that trait
● If all offspring display the dominant phenotype, the
individual in question is homozygous dominant
● if the offspring display both dominant and recessive
phenotypes, than the individual is heterozygous.
Guinea Pig Test Cross
I hand you a black Guinea pig (BB or Bb) and ask you, what
is the genotype?
Preform a test cross to identify genotype of the black Guinea
pig.
To perform an actual test cross with this guinea pig, we
would need a guinea pig (of the opposite sex) that is
homozygous recessive ("bb").
In other words, we would need a white guinea pig to mate
with our black guinea pig.
Work both crosses to determine genotype!