Inheritance%20Patterns%20

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Inheritance Patterns Human Genetics

• Chapter 12

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Chromosomes Inheritance

• Section 12.1

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What makes human males different than females?

• Sex chromosomes (X and Y)
• Male XY
• Female XX
• Gametes
• Egg carry only X
• Sperm carry either X or Y

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Who Discovered Sex Chromosomes?

• Thomas Morgan
• Early 1900s
• Columbia University (USA)
• Worked with fruit flies

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Sex Linkage

• When genes are found on the sex chromosomes
• X-linked Genes genes on the X chromosome
• Y-linked Genes genes on the Y chromosome

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Sex Linked Traits

• Most sex linked genes are found on the X
  chromosome
• Only genes on the Y chromosome are for male
  reproductive organ development

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Sex Linked Genetic Problems

• In flies R red eyes, r white eyes
• Gene located on the X chromosome

X
X
X
Y
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Example 1

• White eye male mates with a red homozygous
  dominant female
• XrY x XRXR

Xr
Y
XRXr
XRY
XR
100 red female 0 white female 100 red
male 0 white male
XRXr
XRY
XR
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Example 2

• Red eye male mates with a red heterozygous female
• XRY x XRXr

XR
Y
XRXR
XRY
XR
100 red female 0 white female 50 red
male 50 white male
XRXr
XrY
Xr
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Example 3

• White eye male mates with a red heterozygous
  female
• XrY x XRXr

Xr
Y
XRXr
XRY
XR
50 red female 50 white female 50 red
male 50 white male
XrXr
XrY
Xr
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Linkage Groups

• Genes located on the same chromosome and
  therefore inherited together
• Goes against Mendels Law of Independent
  Assortment

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How do linked genes get unlinked?

• Crossing Over
• The frequency of crossing over between certain
  genes is used to make a chromosome map

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• Which two genes have the highest probability of
  crossing over? The lowest?

A
a
Highest A C Lowest A B
B
b
C
c
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Chromosome Map
Diagram of the linear order of genes on a
chromosome
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Sex Linkage Problems!!!!

• Use these genotypic symbols for the sex linked
  trait of red-green color blindness in humans to
  solve the problems that follow.
• "Normal" female XBXB
• Carrier female XBXb
• Color-blind female XbXb
• Normal male XBY
• Color-blind Male XbY

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• 1) A normal female marries a color blind male.
  What are the chances that the offspring will be
  color blind if they are females? What are the
  chances that the offspring will be color blind if
  they are males?

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• 2) A color blind female marries a normal male.
  How many of the female offspring will be carriers
  of the color blind allele?

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• 3) A man whose mother is color blind marries a
  woman with normal vision. What is the genotype of
  the husband? What percent of their offspring can
  be expected to be color blind? What percentage of
  their offspring can be expected to be carriers?

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How do biologist keep track of inherited traits
over generations in a family?

• Pedigree (page 241)

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Pedigree Key
Normal male
Marriage
Affected male
Unmarried
Normal female
Dead
Affected female
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Lets try some pedigree problems!
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• R Tongue Roller r No Tongue Roller
• John Jones, a tongue roller, marries Jill Smith,
  a woman that cannot roll her tongue. John and
  Jill have four children that can each roll their
  tongue John Jr., Alice, Lisa, and Sean. John Jr.
  later marries non-tongue roller Pamela, and they
  have four children Jessica, Sherri, Mary, and
  John III. Sherri and Mary both can roll their
  tongues, and Jessica and John III are non-tongue
  rollers. Sean marries Robin, a non-tongue roller.
  Both Robins parents are non-tongue rollers also.
  Sean and Robin have four children Nicholas,
  Harry, Donna, and Sean Jr. Nicholas, Harry and
  Donna each have the ability to roll their
  tongues. Sean Jr. cannot.

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Human Genetics

• Section 12.2

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Human genetics is not as easy as Mendels peas!

• Many patterns of inheritance

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Human Patterns of Inheritance

1. Single allele trait
2. Multiple allele trait
3. Polygenic trait
4. X-linked trait
5. Nondisjunction

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1. Single Allele Trait

• A trait that is controlled by a single allele of
  a gene
• Normal dominant-recessive (Mendel)
• Example Genetic Disorders
• Huntingtons Disease (autosomal dominant)
• Cystic Fibrosis (autosomal recessive)

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2. Multiple Allele Trait

• 3 or more alleles of the same gene code for a
  single trait
• Example ABO Blood Type
• IA type A (dominant)
• IB type B (dominant)
• i type O (recessive)

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Blood Type Problems

• If a person is type A blood.what is his/her
  genotype?
• IAIA or IAi
• If a person is type B blood.what is his/her
  genotype?
• IBIB or IBi
• If a person is type O blood.what is his/her
  genotype?
• ii
• If a person is type AB blood.what is his/her
  genotype?
• IAIB

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Blood Type Problems

• A mother gives birth to a type O child. The
  mother is type A blood. The two potential
  fathers are type A (father 1) and type AB (father
  2).
• Whos the daddy?

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3. Polygenic Trait

• Trait that is controlled by 2 or more genes
• Range of phenotypes
• Influenced by environmental factors too
• Examples
• skin color
• eye color
• human height

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4. X-Linked Trait

• Trait controlled by a gene on the X chromosome
• Examples
• colorblindness (recessive)
• hemophilia (recessive)

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Hemophilia Pedigree
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5. Nondisjunction

• The failure of chromosomes to separate during
  meiosis resulting in one gamete with too many
  chromosomes and one gamete with too few
  chromosomes

Monosomy
Trisomy
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• Trisomy cell with 3 copies of a chromosome (too
  many chromosomes)
• Monosomy cell with 1 copy of a chromosome (too
  few chromosome)
• Example Genetic Disorders
• Down Syndrome (Tri-21)
• Klinefelters Syndrome (XXY)
• Turners Syndrome (X__)

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Mutations that Lead to Genetic Disorders

• Mutation a change in the DNA of an organism
• Can involve an entire chromosome or a single
  nucleotide
• Can lead to genetic disorders

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Mutation Types

• Germ-cell mutation occurs in the germ cells
  (gametes)
• Does not affect the organism
• Does affect the organisms offspring
• Somatic-cell mutation occurs in the organisms
  body cells
• Does affect the organism
• Does not affect the organisms offspring
• Lethal mutation causes death, often before birth

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• Chromosome mutation change in the structure of a
  chromosome
• a. Deletion
• b. Inversion
• c. Translocation
• d. Nondisjunction

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5. Gene mutation involves large segments of DNA
or a single nucleotide of DNA

• a. Point mutation single nucleotide mutation
  within a codon
• b. Frame shift mutation cause the misreading of
  codons during translation thus making the wrong
  protein

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Detecting Human Genetic Disorders

• Before Pregnancy
• Genetic Screening
• Genetic Counseling
• During Pregnancy
• Amniocentesis
• Chorionic Villi Sampling
• After Birth
• Genetic Screening