Patterns of inheritance!

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Patterns of inheritance!
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• Although we are SOOOO thankful for Mendel, there
  are many exceptions to Mendels Laws of
  Heredity.
• Genetics is more complicated!

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Incomplete dominance

• One allele is not completely dominant over
  another

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Incomplete dominance

• Heterozygous offspring have an appearance in
  between the phenotype of the parents!
• Example Snapdragons (flower)
• Red (RR) x White (rr)

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Incomplete dominance

• Heterozygous phenotype is between the dominant
  recessive phenotype!

r
Rr
Rr
All F2 generation Are Rr
Rr
Rr
Rr PINK flowers!!!!!
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Incomplete dominance
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Incomplete dominance
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Quick tip.
Incomplete dominance leads to a blending of the
phenotypes!
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Codominance

• BOTH alleles contribute to
• the phenotype!!!

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Codominance

• When heterozygous, BOTH alleles act
• dominantBOTH alleles
  are seen!
• Example Chickens
• BB black bb white
• BB black feathers
• bb white feathers

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Codominance

• Heterozygous offspring show both phenotypes!!
• Example Chickens
• BB black feathers
• bb white feathers
• All F1 generation are
• Bb
• Bb black and white speckles!

b
b
B
Bb
Bb
B
Bb
Bb
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Codominance in Chickens
P generation
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Codominance is SOOO beautiful!
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Quick tip
Codominance leads to BOTH phenotypes!
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Review

• Mendel Complete Dominance
• Red (RR)
• Red (Rr)
• White (rr)
• Yellow 12
• Incomplete dominance
• -Long tails (L)
• -Short tails (S)

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Multiple Alleles

• Genes that have
• more than two alleles

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• Color coat in rabbits is determined by a
  single gene that has at least four different
  alleles. Different combinations of these alleles
  result in the four colors you see here.

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• In some rabbits, there are four alleles for fur
  color but each rabbit only has two alleles.
  Depending on which two alleles they have, they
  will be one of four colors!
• Red is dominant over Tan, which is dominant over
  Black, which is dominant over Albino
• (R) (T) (B)
  (A)
• Red gt Tan gt Black gt Albino
• If a heterozygous black male rabbit mates with a
  homozygous tan rabbit, what will the babies look
  like?

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Another example of multiple alleles(Codominance,
TOO!)

• Human blood type
• A B O
• Three alleles for one trait!

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Human Blood Type

• Blood type is determined by an antigen found on
  the surface of the blood cell (protein that can
  stimulate the production of antibodies)
• A B O
• Everybody receives one allele for
• blood type from each parent!
• A and B are CODOMINANT!
• O is recessive!

Blood Type Phenotype
AA Blood Type A
AB Blood Type AB
AO Blood Type A
BB Blood Type B
BO Blood Type B
OO Blood Type O
Sothere are FOUR blood types A B
AB O
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Multiple Allele Codominance Problem

• Homozygous male Type B (BB)
• X
• Heterozygous female Type A (AO)
• ½
  AB
• ½ BO
• SO,
  what are there
• actual blood types?

B
B
A
AB
AB
O
BO
BO
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• If a boy has a blood type O and his sister has
  blood type AB, what are the genotypes and
  phenotypes of their parents?

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Quick tip

• Multiple Alleles means
• there are many alleles
• but you still only have two!

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Polygenic Traits

• Traits controlled by two or more genes

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• The wide range of skin color in humans is due to
  more than four different genes that control this
  trait!

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And eye color!
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Quick Tip

• Polygenic traits are more complex than our
  punnett squares!

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Sex-Linked traits

• Genes that are carried on the X or Y chromosomes
• (the sex chromosomes)!
• Ex Colorblindness, Hemophilia and Duchenne
  Muscular Dystrophy

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First, remember how to determine gender

• Females have XX chromosomes
• Males have XY chromosomes

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Sex-Linked traits

• BUTthe X chromosome is BIGGER and holds WAY more
  genes than the Y
• -The Y chromosome appears to only contain a few
  genes total
• -Currently 100 x-linked genetic disorders have
  been mapped

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Sex-Linked Traits

• FEMALES
• XRXr XRXR
• MALES
• XRY XrY

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Carriers

• Since females have two copies of the X
  chromosome, it is possible to have certain
  alleles hidden by a dominant allele. She is a
  healthy CARRIER
• However, because males only have one X
  chromosome, they either have itor they dont.
  They can NOT be carriers!

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B Healthyb Muscular Disorder
FEMALE Bb Healthy Phenotype Carrier MALEb
Muscular Disorder
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Healthy Father, Carrier Mom
2 out of 4 children will have the hemophilia
allele. -The female Carrier -The male HAS
hemophilia
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The infected son has children with a healthy woman

• None of the children would have hemophilia.
• ALL females Carriers
• This is why sex-linked traits often disappear and
  reappear from generation to generation!

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Quick Tip!

• Sex-linked traits affect males and females
  differently!!!

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Genetics and Environment

• Traits are determined by a combination of genes
  and environment!!!

A sunflower gene for height or flower size BUT,
these are influenced by sunlight, soil,
water Genes provide a plan for developmentbut
how that plan unfolds depends on the environment!
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Some more examples.

• -Blood Pressure
• -Intelligence
• -High yielding tomato plant
• -Fair skin prone to cancer
• -Woman baldness

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Practice Problems

• Incomplete dominance
• In a particular species of bird, feather color
  shows incomplete dominance. A cross between a
  blue bird (BB) a white bird (bb) produces
  offspring that are silver (Bb).  If two silver
  birds were to mate, what would the genotypes
  phenotypes be of their babies?

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Practice Problems

• Codominance
• Cow coloration is commonly an example of
  codominance. Homozygous cows can be white or
  brown and heterozygous cows are called roan.
  Describe the appearance of the baby cows if a
  white cow crosses with a brown cow

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Practice Problems

• Multiple Alleles
• In one kind of mouse, fur color is a multiple
  allele trait because there are three alleles.
  Black (B), Tan (T), and white (W) are all alleles
  that mice can have but each mouse only has two
  alleles.
• Black is dominant over Tan, which is dominant
  over White.
• Often written Black gt Tan gt White
• If a homozygous black mouse mates with a
  heterozygous tan mouse, what will the genotypes
  phenotypes be of the offspring?

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Practice Problems

• Sex Linked Trait
• The bison herd on Konza Prairie shows a sex
  linked genetic defect carried on the X
  chromosomes. Some males have a malformed back
  leg that interferes with its normal motion. If a
  healthy male bull mates with a female cow that is
  a carrier, what are the chances of producing a
  normal son?
• Male Genotype Female Genotype
• If he mates with this cow every year, what
  percentage of their daughters will have normal
  knees?
• What percentage of their daughters will be
  carriers of this disease?