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Patterns of Heredity and Human Genetics

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PATTERNS OF HEREDITY AND HUMAN GENETICS Chapter 12 Objectives: Interpret a pedigree Determine human genetic disorders that are caused by inheritance of recessive alleles – PowerPoint PPT presentation

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Title: Patterns of Heredity and Human Genetics


1
Patterns of Heredity and Human Genetics
  • Chapter 12
  • Objectives
  • Interpret a pedigree
  • Determine human genetic disorders that are caused
    by inheritance of recessive alleles
  • Predict how a human trait can be determined my a
    simple dominant allele

2
Mendelian Inheritance of Human Traits
  • How can we trace traits in our family?
  • Geneticists use a tool called a pedigree (graphic
    representation of genetic inheritance)

3
  • Male
  • Female
  • Mates
  • Heterozygous or carrier

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  • I, II, III represent generations
  • pedigrees are used by genetic counselors to help
    trace genetic disorders and other traits

7
Simple Recessive Heredity
  • most genetic disorders are caused by recessive
    alleles (rare) you have to receive 2 alleles, 1
    from mom and 1 from dad in order to inherit the
    disorder

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Examples
  • Cystic Fibrosis (CF)
  • 1/2000 are affected by CF, 1/200 are carriers
  • characterized by a defective protein that causes
    mucas to build up in the lungs

10
  • Tay Sachs Disease
  • common in Ashkenazi Jews
  • characterized by the absence of an enzyme that
    breaks down fat in the brain
  • most children die by the age of 5

11
Simple Dominant Heredity
  • only need a single dominant allele for the trait
    to be expressed

12
  • examples of dominant traits in humans
    unattached ear lobes, tongue rolling, hitchhikers
    thumb, mid digit hair

13
Examples of dominant genetic disorders
  • Huntingtons Disease
  • doesnt affect individuals until their 30-50
    years of age
  • characterized by the breakdown of areas of the
    brain

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12-2 Whey Heredity follows different rules
  • Distinguish between incompletely dominant and
    codominant alleles
  • Compare multiple allelic and polygenic
    inheritance
  • Analyze the pattern of sex-linked inheritance
  • Summarize how internal and external environments
    affect gene expression
  • SCS

16
Complex Patterns of Heredity
  • most traits observed are not a result of simple
    dominant/ recessive inheritance

17
Types
  • Incomplete dominance- heterozygous condition
    results an intermediate phenotype or mixing
    neither allele is completely dominant over the
    other

18
  • Example Snap dragons. Homozygous Red and white
    flowers are crossed, and they produce all pink
    offspring

19
  • Codominance- both alleles are expressed equally
  • Example Cows. Homozygous Red and white cows
    are crossed (mated), and they produce offspring
    that appear pink from a distance because they
    both red and white hairs

20
  • Multiple Alleles- traits controlled by two or
    more alleles

21
  • Sex linked inheritance- traits controlled by
    genes located on the sex chromosomes
  • Thomas Morgan was the first to discover
  • Worked with fruit flies

22
Problems involving sex linkage
  • In fruit flies, red eyes are dominant over white
  • example of a cross
  • XRXr x XrY

23
Polygenic Inheritance-
  • traits that are controlled by more than 1 gene
  • Genes might be on the same or different
    chromosomes

24
  • Other factors influence the expression of genes
  • Environmental Influences
  • External Environmental (temp. nutrition, light,
    chemicals, infectious agents)
  • Internal Environment (hormones, age)
  • genetic makeup determines the potential to
    develop and function

25
12-3 Complex Inheritance of Human Traits
  • Compare codominance, multiple alleleic,
    sex-linked, and polygenic patterns of inheritance
    in humans
  • Distinguish among conditions in which extra
    autosomal or sex chromosomes exist

26
Complex Inheritance of Human Traits
  • Codominance-
  • Sickle Cell Anemia
  • most common in black Americans

27
  • Characterized by the sickling of red blood cells,
    which hampers circulation and affects oxygen
    levels of the blood
  • In malaria prone areas people with this gene are
    protected against malaria

28
  • Homozygous conditions results in full blown SC,
    and medication has to be taken
  • Heterozygous condition results in a mild case,
    may not need medication

29
Multiple Alleles
  • Blood types
  • There are 4 blood types in humans (A, B, AB, and
    0)
  • the type of marker (protein on your red blood
    cells determine your blood type)

30
  • Phenotypes Genotypes
  • Type A IAIA or IA i
  • Type B IBIB or IBi
  • Type AB IAIB
  • Type O ii

31
  • knowing your blood type is important
  • blood transfusions, child birth, blood donations

32
  • Type Blood
  • Can Receive
  • A A, O
  • B B, O
  • AB AB, O, A, B Universal recipient AB
  • Universal Donor O

33
Sex Linkage
  • Some human traits are determined by genes found
    on the sex chromosomes (mostly X)
  • Examples of sex linked traits
  • Red/Green Color Blindness- cant differentiate
    red from green
  • recessive disorder
  • More males have it because they only need one
    allele

34
  • Hemophilia
  • bleeders disease blood does not clot naturally
    so a person can bleed to death
  • 1/10,000 males are afflicted, only 1/ 100 million
    females are affeced

35
Polygenic Traits
  • example include skin color, eye color,

36
Changes in chromosome number
  • Normally humans have 46 chromosomes, but
    sometimes during replication, chromosomes do not
    separate correctly

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  • Geneticist use a tool called a karyotype to
    determine if an extra chromosome is present
  • Take a sample of a persons DNA and line up the
    metaphase chromosomes

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Examples of Disorders
  • Downs Syndrome (Trisomy 21)
  • a result of an extra chromosome in the 21st pair
  • some degree of mental retardation

43
  • Turners Syndrome
  • XO, female, infertile
  • Kleinfelters
  • XXY, Male, infertile
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