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Patterns of inheritance!

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Title: Patterns of inheritance!


1
Patterns of inheritance!
2
  • Although we are SOOOO thankful for Mendel, there
    are many exceptions to Mendels Laws of
    Heredity.
  • Genetics is more complicated!

3
Incomplete dominance
  • One allele is not completely dominant over
    another

4
Incomplete dominance
  • Heterozygous offspring have an appearance in
    between the phenotype of the parents!
  • Example Snapdragons (flower)
  • Red (RR) x White (rr)

5
Incomplete dominance
  • Heterozygous phenotype is between the dominant
    recessive phenotype!

r
Rr
Rr
All F2 generation Are Rr
Rr
Rr
Rr PINK flowers!!!!!
6
Incomplete dominance
7
Incomplete dominance
8
Quick tip.
Incomplete dominance leads to a blending of the
phenotypes!
9
Codominance
  • BOTH alleles contribute to
  • the phenotype!!!

10
Codominance
  • When heterozygous, BOTH alleles act
  • dominantBOTH alleles
    are seen!
  • Example Chickens
  • BB black bb white
  • BB black feathers
  • bb white feathers

11
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
12
Codominance in Chickens
P generation
13
Codominance is SOOO beautiful!
14
Quick tip
Codominance leads to BOTH phenotypes!
15
Review
  • Mendel Complete Dominance
  • Red (RR)
  • Red (Rr)
  • White (rr)
  • Yellow 12
  • Incomplete dominance
  • -Long tails (L)
  • -Short tails (S)

16
Multiple Alleles
  • Genes that have
  • more than two alleles

17
  • 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.

18
  • 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?

19
Another example of multiple alleles(Codominance,
TOO!)
  • Human blood type
  • A B O
  • Three alleles for one trait!

20
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
21
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
22
  • If a boy has a blood type O and his sister has
    blood type AB, what are the genotypes and
    phenotypes of their parents?

23
Quick tip
  • Multiple Alleles means
  • there are many alleles
  • but you still only have two!

24
Polygenic Traits
  • Traits controlled by two or more genes

25
  • The wide range of skin color in humans is due to
    more than four different genes that control this
    trait!

26
And eye color!
27
Quick Tip
  • Polygenic traits are more complex than our
    punnett squares!

28
Sex-Linked traits
  • Genes that are carried on the X or Y chromosomes
  • (the sex chromosomes)!
  • Ex Colorblindness, Hemophilia and Duchenne
    Muscular Dystrophy

29
First, remember how to determine gender
  • Females have XX chromosomes
  • Males have XY chromosomes

30
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

31
Sex-Linked Traits
  • FEMALES
  • XRXr XRXR
  • MALES
  • XRY XrY

32
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!

33
B Healthyb Muscular Disorder
FEMALE Bb Healthy Phenotype Carrier MALEb
Muscular Disorder
34
Healthy Father, Carrier Mom
2 out of 4 children will have the hemophilia
allele. -The female Carrier -The male HAS
hemophilia
35
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!

36
Quick Tip!
  • Sex-linked traits affect males and females
    differently!!!

37
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!
38
Some more examples.
  • -Blood Pressure
  • -Intelligence
  • -High yielding tomato plant
  • -Fair skin prone to cancer
  • -Woman baldness

39
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?

40
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

41
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?

42
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?
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