Inheritance Patterns and Human Genetics

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Chapter 12
Royal Hemophilia

• Inheritance Patterns and Human Genetics

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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

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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

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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

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P XRXR x Xr Y
Xr  Y
XR  XRXr  XRY
  XR XRXr  XRY
Xr  Y
XR 
  XR
Phenotype ratio 100 wild type
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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
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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
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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.

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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.

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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.

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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
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Detecting Genetic Diseases

• Amniocentesis
• The Pedigree

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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
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Sample Pedigrees
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Human Genetic Disorders

• Color blindness
• Hemophilia
• Cystic fibrosis
• Huntingdons disease
• Tay Sachs
• Sickle cell anemia

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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.

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If normal color vision, you will see a 5. If
colorblind, you see a 2
Youtube test
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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

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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

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Multiple Alleles

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

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

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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

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• 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

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• 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
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• Trisomy 21
• Down syndrome
• Extra 21 Chromosomes

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

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46XX 45X0
47XXY 46XY Descriptions
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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
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What to do to help?
GENE THERAPY
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Other neat stuff
X chromosome inactivation and Barr bodies