Codominant vs Incomplete Dominant- What

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Codominant vs Incomplete Dominant- Whats the
difference?
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Beyond Dominant and Recessive

• Incomplete Dominance
• One allele is not completely dominant over the
  other something in the middle is expressed
• Ex. Red and White Snapdragons
• Result can be heterozygous (Rr) or two separate
  dominant alleles (RW)? each resulting in a
  mixture of both alleles

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Another way that incomplete dominance can be
expressed

• Red RR
• White WW
• RW pink- each allele is equally expressed to
  result in a blended product

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One way to express incomplete dominance

• RR (Red) X rr (White) (Rr)Pink
• Rr- results in a blended result of PINK

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Incomplete Dominance Practice

• In certain cats, tail length is determined by a
  gene that demonstrates incomplete dominance. The
  allele that causes a long tail (T) is not
  completely dominant over the allele that causes
  no tail (t). If a cat is heterozygous forthis
  trait (Tt), then the cat will have a short tail.
  What is the probability that the offspring will
  be manx cats (no tail) if a short tailed cat is
  bred with a manx cat (no tail)?

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Incomplete Dominance Practice

• Incomplete dominance is seen in snapdragons. The
  allele that causes red flowers (F) is not
  completely dominant over the allele that causes
  white flowers (f). When a plant is heterozygous
  for the trait of flower color (Ff), pink flowers
  result. Cross two pink snapdragons, and provide
  the genotype and phenotype of all offspring.

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Beyond Dominant and Recessive

• Codominance
• Both alleles are expressed in the phenotype
• Ex. Cow Hair Color
• RR Red
• WW White
• RW Roan (Red White)
• Practice
• Codominance/Incomplete Dominance 1-4

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Beyond Dominant and Recessive

• Multiple Alleles
• Genes have more then two alleles
• Ex. Blood Type
• Type A blood- AA or AO alleles
• A is dominant to O
• Type B blood- BB or BO alleles
• B is dominant to O
• Type AB- codominant- A and B alleles
• A nor B is dominant so both are expressed on
  organisms RBC
• Type O- recessive- OO alleles
• Both alleles must be recessive in order to
  have type O.

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• More on blood types..
• The blood type determines what antibodies are
  located within the blood. Type A blood has type B
  antibodies. If type B blood is put into their
  bodies, their immune system reacts as if it were
  a foreign invader, the antibodies clump the blood
  - can cause death.
• Type AB blood has no antibodies, any blood can be
  donated to them - they are called the "universal
  acceptors"
• Type O blood has no surface markers on it,
  antibodies in the blood do not react to type O
  blood, they are called the "universal donors"

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Co-dominance Practice

• In humans, blood types A and B are equally
  dominant (codominant). Both types are dominant to
  type O. A man with type AB blood marries a woman
  with type O blood. Give the genotypes and
  phenotypes of all possible offspring.

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Co-dominance Practice

• If a man with blood type A, one of whose parents
  had blood type O, marries a woman with blood type
  O, what percentage of their offspring would have
  blood type OO?

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Polygenic Traits

• Traits that are controlled by the interaction of
  several genes.
• Example
• Reddish brown eyes in varying degrees found in
  fruit flies is controlled by 3 genes
• Human skin color is controlled by 4 different
  genes which result in a variety of skin color.

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Sex-linked Genetics
Ex. Colorblindness
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Sex Chromosomes- last pair (23rd) in a karyotype
MALE KARYOTYPE
FEMALE KARYOTYPE
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Sex Chromosomes- last pair (23rd) in a karyotype

• Male XY and Females XX
• The 23rd pair of chromosomes will determine the
  gender of an individual
• Very few genes are located on the Y
  chromosomeMost are located on the X
• Sex linked alleles will ALWAYS be tracked on the
  X chromosome ONLY when we conduct practice
  genetic problems

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Sex-Linked Genes

• Ex. Colorblindness is carried on the
  sex-chromosomes
• It is a recessive trait Xc
• How many genes do females need to express the
  trait (colorblindness)?
• 2 Xc Xc
• How many genes do males need to express the
  trait (colorblindness)?
• 1 XcY

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Sex-Linked Punnett Square

• Let C Normal Vision and c Colorblind
• Cross Normal Male ( ) x Carrier Female (
  )

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Sex-Linked Punnett Square
C

• Let C Normal Vision and c Colorblind
• X Y x X X Normal Male x Carrier Female
• X
  Y
• X
• X

C
C
c
C
1st put male genotype on the top of the table
female genotype on the left side



C
c
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Sex-Linked Punnett Square
C

• C Normal Vision and c - Colorblind
• X Y x X X - Normal Male x Carrier Female
• X
  Y
• X
• X

C
C
c
C
2nd, cross them


X X X Y X X
X Y
C
C
C
C
C
c
c
c
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Sex-Linked Punnett Square
C

• C Normal Vision and c - Colorblind
• X Y x X X -Normal Male x Carrier Female
• X
  Y
• X
• X

3rd, list the sex and appearance of each possible
offspring
C
C
c
C
Offsprings 1 Normal Female 1 Normal (Carrier)
Female 1 Normal Male 1 Colorblind Male


X X X Y X X
X Y
C
C
C
C
C
c
c
c
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Sex-linked Practice

• Hemophilia is a disease caused by a gene found on
  the X chromosome. Therefore, it is referred to as
  a sex linked disease. The recessive allele
  causes the disease. A normal man marries a woman
  that is heterozygous for the trait. Give the
  genotypes and phenotypes of all possible
  offspring. Will any of their children have the
  disease?

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PRACTICE and HW

• Complete problems 1-3 on the sex linked genetic
  practice problems sheet NOW!
• Complete the remaining 3 Co-dominant and
  Incomplete dominant practice problems and Sex
  Linked practice problems 4-8 from todays class
  for HW