Download Incomplete Dominance

Part 2:
Non-Mendelian
Genetics
Last week we learned about
Mendelian Genetics
• This week we will learn about Complex
Patterns of Inheritance.
• Complex Inheritance - does not follow the
patterns that Mendel described.
Exceptions to Simple
Dominance
1. Incomplete Dominance
2. Co-dominance
3. Multiple Alleles
4. Sex-linked
• Incomplete DominanceWhen the heterozygous
phenotype is an
intermediate (mix)
between those of the
two homozygous
parents.
Example
• AA=red Aa=pink
aa=white
Incomplete Dominance
(One allele for a specific trait is not completely dominant over the other
allele. This results in a blended phenotype.)
Genotype
Phenotype
Example
Homozygous
Dominant
Dominant
Curly hair
Heterozygous
Dominant
Intermediate
(blend)
Wavy hair
Homozygous
Recessive
Recessive
Straight hair
Practice Problem: Incomplete
Dominance
• A wildcat comes in three colors: blue, red,
and purple. A homozygous dominant (BB)
individual is blue, a homozygous recessive
(bb) individual is red, and a heterozygous
(Bb) individual is purple. What would be
the genotypes and phenotypes of the
offspring if a blue wildcat were crossed
with a red one?
Key:
BB=blue
Bb=purple
bb=red
P1 Cross
Blue X
BB X
Red
bb
F1
Genotype
:
Phenotyp
e:
Co-dominance - both alleles are
expressed. Neither allele is
dominant over the other.
Sickle Cell
Co-dominance
(Forms of the gene are equally dominant to each other.)
Genotype
Phenotype
Example
Homozygous
Dominant
Dominant
Red horse hair
Heterozygous
Dominant
Homozygous
Recessive
Intermediate
Roan hair
(both alleles
(red AND white)
are expressed)
Recessive
White horse
hair
Practice Problem: Co-dominance
• In cattle, reddish coat color is not
completely dominant to white coat color.
Heterozygous individuals have coats that
are roan colored (ie. reddish, but with spots
of white hairs).
• Show a cross of a homozygous dominant
red bull with a roan cow.
• (Hint roan is heterozygous.)
Key:
BB= Red
Bb= Roan
bb= White
(both of red and white)
P1 Cross
Red X
BB X
Roan
Bb
F1
Genotype
:
Phenotyp
e:
Co-Dominance Vs. Incomplete Dominance
Make a poster with a fictitious Animal or plant illustrating CoDominance and Incomplete Dominance.
1. Give your new organism a name and title your poster.
2. Make a “key” with the genotypes and phenotypes listed.
3. List the parent’s genotypes and draw a small image of each.
Then draw one offspring. List the genotype. (See example.)
4. List and Define the Vocab word at the bottom of the poster.
5. Must be COLORED and NEAT!!
You may NOT copy my example! Think of something ORIGINAL!!!
Warm-up Questions
• What is Incomplete Dominance?
• What is Co-dominance?
• How are they different from each other?
• How are the different from Complete Dominance
(Simple Dominance)?
Multiple Alleles- having more than
2 alleles for one specific trait
• Remember a gene is an inherited trait (hair
color). An allele is a form of that gene
which codes for the phenotype (brown,
blond, red, etc).
Multiple Alleles
(Multiple alleles can demonstrate a hierarchy of dominance)
in this example, there a 4 possible alleles: M, mb , mc , m
Genotype
Phenotype
MM, Mmb, Mmc, Mm Dominant to all
others
Example
Ace beats the
mbmb, mbmc, mbm
Version b
King beats the
(dominant to mc & m)
Queen & Jack
mcmc, mcm
mm
King, Queen,
Jack
Version c (dom. Queen beats
the Jack
to rec.)
Recessive to
all others
The hair color of chinchillas would be an example of a multiple allelic trait.
Jack
Blood cells are an example of multiple alleles
and Co-Dominance
As you can count, there are 6 different genotypes &
4 different phenotypes for blood type.
Bottom line for Multiple alleles
• The presence of multiple alleles allows for
an increased number of genotypes and
phenotypes, thus creating more variation.
• Why might variation be a good thing????
Practice Problem: Multiple
alleles
• A woman with
Type O blood and
a man who is Type
AB have are
expecting a
child. What are
the possible blood
types of the kid?
Type O X Type AB
This Chart will Always be provided for you
• Worksheet Multiple Alleles what’s not
done is HW
Sex Linked
• Sex linked traits - characteristic controlled
by genes that are on the X chromosome.
*Remember*
Male Genotype: XY Female Genotype: XX
Sex-linked
(traits carried on sex chromosome, usually X-linked)
Genotype
Phenotype
Example
XX
XY
Non-afflicted,
not a carrier
Normal female
Normal male
XcX
Carrier but
not afflicted
XcXc
XcY
Both are
afflicted
Carrier female
*males cannot be
carriers!
Colorblind
female & male
C = colorblindness which is a recessive, se
Why are more
males affected
by X-linked
traits than
females?
Why are more males affected by
X-linked traits than females?
• Males have an XY genotype, since males
have only one X chromosome, they are
affected by recessive X linked traits more
often than females.
• Females have an XX genotype and the other
X chromosome would likely mask the
recessive trait.
Sex-Linked Traits
• Can you see a number
inside this circle?
• About 8% of males a
color blind and only
.5% of females
Punnett Square
• XB = Normal
• Xb = affected trait
• Y= Normal Y
chromosome
XB
Y
XB XBXB XB Y
Xb XBXb Xb Y
Practice problem: Sex-linked
• Hemophilia is due to a sex-linked recessive
gene (Xh) and the normal condition to the
gene (XH). Show a cross between a
hemophiliac man and a woman does not
carry the trait.
hemophiliac man X normal woman
Key
Xh =
Normal
XH =
Hemophiliac
*Remember*
Male Genotype: XY Female
Genotype: XX
• Sex linked traits WS what’s not done is HW
Lets review our new terms!!
• Sex linked traits- characteristic controlled by
genes that are on the X chromosome.
• Incomplete dominance- When the heterozygous
phenotype is intermediate between those of the
two homozygous parents.
• Codominance- both alleles are expressed, neither
allele is dominate over the other
• Multiple alleles- having more than 2 alleles for a
specific trait