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Inheritance Patterns and Human Genetics

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Chapter 12 Inheritance Patterns and Human Genetics Disorder Symptom Pattern of Inheritance Frequency at birth Huntington's disease Deterioration of brain tissue ... – PowerPoint PPT presentation

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Title: Inheritance Patterns and Human Genetics


1
Chapter 12
Royal Hemophilia
  • Inheritance Patterns and Human Genetics

2
How is your sex determined?
  • Thomas Hunt Morgan (1866-1945)
  • Won the Nobel Prize in 1933 for work with fruit
    flies Drosophila their white-eyed mutation.
  • Found that Drosophila had 4 pairs of chromosomes
    with 1 mismatched pair
  • Males XY
  • Females XX.
  • True for all mammals and most insects
  • Always a 5050 chance of getting a male or female
    offspring

3
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4
Why work with fruit flies?
  • .5mm long
  • Fast reproductive cycle
  • Embryo develops 1 day after fertilization to
    become a larva
  • Pupa 2 days later
  • 4 more days to emerge as an adult
  • Fertile with 8 - 12 hours after hatching
  • Need only a small area to culture many
  • Reproduce many offspring

5
Since Y chromosome is so small, could genes be
located on the X chromosome that are not on the Y
chromosomes?
  • Sex Linkage
  • traits that are determined by whether you are
    male or female
  • Normal fruit flies (wild type) are Red eyed
  • Morgan crossed a white eyed male and a red
    eyed female fruit fly.
  • All F1 were wild type fruit flies
  • Did an F1 cross.
  • ½ the males were white eyed but no females had
    the white eyes

6
P XRXR x Xr Y
Xr  Y
XR  XRXr  XRY
  XR XRXr  XRY
Xr  Y
XR 
  XR
Phenotype ratio 100 wild type
7
F1 cross XRXr x XRY
XR   Y
 XR XRXR  XRY 
Xr  XRXr  XrY 
XR   Y
 XR
Xr 
F1 cross XRXr x XRY
Phenotype ratio 75 wild type 25 white eyed
100 of females will be wild type 50 of
males could be white eyed
8
What cross would yield a white eyed female?
XRXr x XrY
Xr    Y
 XR XRXr  XRY 
Xr  XrXr  XrY 
Phenotype 5050 for males and females for white
or wild type eyes
9
Human Sex Chromosomes
ltgt
  • The X chromosome is much larger than the Y
    chromosome.
  • Genes that are located on the top of the X
    chromosome are not on the Y chromosome
  • Males either have the trait or are normal
  • Females can be carriers for the traits.

10
Linked Genes
  • Genetic linkage is the tendency of alleles found
    on a chromosome to be inherited together during
    meiosis
  • Genes nearer to each other are less likely to be
    separated onto different chromatids during
    crossover, and are genetically linked
  • The nearer two genes are on a chromosome, the
    lower is the chance of a swap occurring between
    them, and the more likely they are to be
    inherited together.

11
Chromosome Mapping
  • A genetic map is a map based on the frequencies
    of recombination between markers during crossover
  • The greater the frequency of recombination
    between two genetic markers, the further apart
    they are assumed to be
  • Conversely, the lower the frequency of
    recombination between the markers, the smaller
    the physical distance between them.

12
Sex-linked traits in humans
  • Red-Green color blindness recessive. Cant
    distinquish between colors
  • Muscular dystrophy- recessive weakens then
    destroys muscle tissue
  • Hemophilia recessive lacks ability to produce
    clotting factor bleeders
  • Ran rampant through the royal families of Europe
    Royal Hemophilia

Queen Victoria
Czar Nicholas II
13
Detecting Genetic Diseases
  • Amniocentesis
  • The Pedigree

14
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15
How could you trace a trait throughout a family?
  • Pedigree
  • shows how a trait is inherited over several
    generations

Female Female with the trait
Male Male with the
trait If half colored in, they are a carrier of
the trait
16
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17
Sample Pedigrees
18
Human Genetic Disorders
  • Color blindness
  • Hemophilia
  • Cystic fibrosis
  • Huntingdons disease
  • Tay Sachs
  • Sickle cell anemia

19
Here is a test for you. Look at the figures below
and write down what you see. Do not talk or make
any comments during this test!
.
4.
If you could not see the 29, 45, 56, 6 or 8, you
are color blind!! 12 20 of the population has
this trait.

20
If normal color vision, you will see a 5. If
colorblind, you see a 2
Youtube test
21
Sex influenced trait
  • Males and females express trait differently with
    the same phenotype
  • Male Pattern Baldness recessive speaks for
    itself!
  • On autosomes, not sex linked
  • XNXN XNYN - Normal hair
  • XNXn XNYn - Normal female, Bald male
  • XnXn XnYn - Bald

22
How does the inheritance of traits located on the
same chromosome affect how they are inherited?
  • Linkage groups
  • If genes are located on the same chromosome, they
    tend to be inherited together
  • Morgan - genes for wing length and body color
    were on the same chrom (linked)
  • Crossing over during Prophase I of Meiosis
    unlinks linked genes
  • The closer two genes are on a chromosome, the
    less likely they are to cross over. gt
    probability of crossing over the further away
    they are on a chrom

23
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24
Multiple Alleles
  • Traits controlled by 3 or more alleles for a
    given trait
  • Blood type IA IB i (A, B, O)

25
  • Polygenic inheritance
  • 2 or more genes determine a single trait. Ends
    up blending these genes
  • Height
  • Skin pigmentation
  • Eye color
  • Hair color

26
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27
What can go wrong? AKA Mutations
  • Germ cell mutations
  • affect gametes
  • may be passed on to offspring
  • 2. Somatic mutations
  • affect body cells
  • not inheritable
  • Some cancers leukemia

28
  • Chromosomal mutations
  • changes in structure of a chromosome or
    addition or loss of an entire chromosome
  • Deletion/addition portion of chrom is missing
    or added
  • Inversions pieces of chroms flip flop
  • Translocations pieces of nonhomologous chroms
    are exchanged
  • A lovely British animation

29
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30
  • Nondisjunction
  • type of Chromosomal mutation
  • entire chromosomes are missing or extra
    chromosomes
  • Chromosomes fail to separate during meiosis
  • Results in gametes with extra chromosomes or
    missing chromosomes

Animation
31
  • Trisomy 21
  • Down syndrome
  • Extra 21 Chromosomes

32
  • If Sex chromosomes fail to disjoin
  • Turners syndrome X0 female
  • Klinefelters syndrome XXY male

33
46XX 45X0
47XXY 46XY Descriptions
34
Disorder Symptom Pattern of Inheritance Frequency at birth
Huntington's disease Deterioration of brain tissue - middle age Autosomal dominant 1/10,000
Cystic fibrosis Mucus clogs lungs, liver pancreas - doesn't make it to adulthood autosomal recessive 1/2,080 (whites)
Sickle cell anemia Impaired blood circulation - organ damage autosomal recessive? 1/500 (African decent)
Tay-Sachs disease Deterioration of central nervous system - childhood death autosomal recessive 1/1,600 (European Jewish decent)
Phenylketonuria Brain failure - doesn't have enzyme for phenylalanine digestion autosomal recessive 1/18,000
Hemophilia Failure to clot blood X-linked recessive 1/7,000
Muscular dystrophy wasting away of muscles X-linked recessive 1/10,000
Genetic Disorders
35
What to do to help?
GENE THERAPY
36
Other neat stuff
X chromosome inactivation and Barr bodies
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