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Chapter 11 Complex Inheritance and Human Heredity

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Title: Chapter 11 Complex Inheritance and Human Heredity


1
Chapter 11 Complex Inheritance and Human
Heredity
  • Section 3 Chromosomes and Human Heredity

2
Karyotype Studies
  • A karyotype shows the pairs of homologous
    chromosomes arranged in decreasing size
  • The chromosomes are stained during metaphase
  • The staining bands identify identical places on
    homologous chromosomes
  • Human karyotypes show the 23 pairs of chromosomes
    seen in humans
  • 22 pairs of autosomes and 1 pair of sex
    chromosomes

3
Male and Female Karyotypes
Female
Male
4
Telomeres
  • Scientist have found that chromosomes end in
    protective caps called telomeres
  • The cap protects the structure of the chromosome,
    and is shortened after each round of DNA
    replication
  • Scientists have discovered that telomeres might
    play a role in aging and cancer

5
Nondisjuction
  • During cell division, sister chromatids are
    separated and move to opposite poles of the cell
  • Cell division in which sister chromatids fail to
    separate is called nondisjunction
  • If nondisjunction occurs during meiosis, the
    resulting gametes will not have the proper number
    of chromosomes
  • If this gamete is used in fertilization, the
    resulting organism will not have the correct
    number of chromosomes!

6
Nondisjunction
  • Having three copies of a chromosome is called
    trisomy
  • Having only one copy of a chromosome is called
    monosomy
  • Nondisjunction can occur in ANY organism that
    produces gametes through meiosis
  • In humans, nondisjunction results in serious
    disorders, many of which are fatal!

7
Down Syndrome
  • Down Syndrome is caused when an individual has an
    extra copy of chromosome 21
  • Often called trisomy 21
  • Characteristics of Down Syndrome are
  • Distinctive facial features
  • Short stature
  • Heart defects
  • Mental disability
  • 1 out of 800 babies are borne with Down Syndrome
    in the United States
  • The frequency of Down Syndrome increases with the
    age of the mother

8
Down Syndrome
9
Sex Chromosomes
  • Nondisjunction can occur with sex chromosomes as
    well
  • Female Disorders
  • Genotype XX
  • Phenotype Normal Female
  • Genotype XO
  • Phenotype Female with Turners Syndrome
  • Effects Short in stature if untreated, ovaries
    underdeveloped which will affect puberty, usually
    infertile
  • Genotype XXX
  • Phenotype Nearly normal female

10
Sex Chromosomes
  • Male Disorders
  • Genotype XY
  • Phenotype normal male
  • Genotype XXY
  • Phenotype Male with Klinefelters Syndrome
  • Effect Will not produce normal levels of
    testosterone (leads to smaller testes and lack of
    body hair), usually do not produce sperm
  • Genotype XYY
  • Phenotype Normal or nearly normal male
  • Genotype OY
  • Phenotype Results in death

11
Fetal Testing
  • Individuals who believe they might be carriers
    for a genetic disorder can have fetal testing
    performed.
  • There are three options for fetal testing
  • Amniocentesis
  • Chorionic Villus Sampling
  • Fetal Blood Sampling

12
Amniocentesis
  • How test is performed
  • A long, thin needle is inserted into the
    fluid-filled sac that surrounds the baby
  • 2 tablespoons of fluid is drawn
  • Benefit
  • Diagnosis of chromosome abnormalities
  • Diagnosis of other defects
  • Risks
  • Discomfort for expectant mother
  • Slight risk of infection
  • Risk of miscarriage

13
Amniocentesis
14
Chorionic Villus Sampling
  • How test is performed
  • Using a catheter, a sample of chorionic villi
    cells containing the babys DNA is taken from the
    placenta
  • Benefit
  • Diagnosis of chromosome abnormality
  • Diagnosis of certain genetic defects
  • Risks
  • Risk of miscarriage
  • Risk of Infection
  • Risk of newborn limb defects

15
Chorionic Villus Sampling
16
Fetal Blood Sampling
  • How test is performed
  • A long, thin needle is inserted into the mothers
    abdomen and a blood sample is taken from the
    umbilical cord or from the fetuss liver/heart
  • Benefit
  • Diagnosis of genetic or chromosome abnormality
  • Checks for fetal blood problems and oxygen levels
  • Medications can be given to the fetus before
    birth
  • Risks
  • Risk of bleeding from sample site
  • Risk of infection
  • Amniotic fluid might leak
  • Risk of fetal death

17
Fetal Blood Sampling
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