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Chapter 14-1: Human Heredity

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Chapter 14-1: Human Heredity Human chromosomes Most of our cells contain 23 pairs of chromosomes, for a total of 46 chromosomes. These cells are called somatic cells ... – PowerPoint PPT presentation

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Title: Chapter 14-1: Human Heredity


1
Chapter 14-1Human Heredity
2
Human chromosomes
  • Most of our cells contain 23 pairs of
    chromosomes, for a total of 46 chromosomes.
  • These cells are called somatic cells or body
    cells.
  • Two exceptions are the gametes (sex cells), sperm
    and eggs, which have one copy of each chromosome.
    Sperm and egg cells each have 23 chromosomes.

3
Human chromosomes
  • There are two types of chromosomes.
  • Autosomes Of the 46 chromosomes, 44 of them (22
    pairs of chromosomes) are called autosomes
    (non-sex chromosomes).
  • Sex chromosomes The last two chromosomes are
    called the sex chromosomes because they determine
    the sex of the person. Females have two X
    chromosomes (XX) and males have one X and one Y
    chromosome (XY).

4
  • Gametes
  • All gametes are haploid. In humans, that means
    each egg cell and each sperm cell has 1 copy of
    each chromosome for a total of 23 chromosomes.
  • Egg cells All human egg cells carry 23
    chromosomes, one of which is a single X
    chromosome. This is written as 23, X.
  • Sperm cells In males, there are two types of
    sperm cells- one carries an X chromosome (23, X)
    and one carries a Y chromosome (23, Y).

5
  • When a sperm and egg cell combine, half of the
    time the fertilized eggs (also called zygotes)
    are female (46, XX) and half of the time they are
    male (46, XY).

X
X
eggs
X
XX
XX
female
female
Y
XY
XY
male
male
sperm
6
  1. Scientists can analyze chromosomes by taking a
    picture of cells during mitosis. It is easiest
    to view chromosomes during mitosis because they
    are condensed. From a picture of chromosomes,
    scientists can cut and paste to arrange the
    chromosomes in pairs to form a karyotype. They
    are arranged from largest (pair 1) to smallest
    (pair 22). The last pair (23) is the sex
    chromosomes.

7
Karyotype
Y
X
8
Male or Female?
Male
Female
9
Human Traits
  • A pedigree is similar to a family tree- both are
    used to show relationships in a family.
  • Pedigrees can be used to demonstrate how traits
    are passed from one generation to another.
  • Genetic counselors use pedigrees to follow how
    genetic disorders are inherited.
  • People who are heterozygous for a recessive
    genetic disorder (they are unaffected) are called
    carriers.

10
female
male
children
marriage
parents
11
Add to your notes Sometimes, but not always,
carriers of traits (heterozygotes) may be
represented as a half-shaded shape or a shape
with a dot in the middle.
12
Human Genes Blood typing
  • In humans, blood type is determined by the Rh
    blood group and the ABO blood group.
  • The Rh blood group determines if your blood is
    positive or negative.
  • There are two Rh alleles the Rh allele is
    dominant to the Rh- allele.
  • Your blood is positive if you are Rh /Rh or
    Rh/Rh-. Your blood is negative if you are Rh-/Rh-

13
  • The ABO group is more complicated. There are
    three alleles IA, IB, and i.
  • The IA and IB alleles are codominant. The IA and
    IB alleles cause expression of carbohydrate
    chains called antigens on surface of red blood
    cells. They help your body identify the cells.
  • The i allele is recessive to the other two
    alleles. The i allele O does not produce
    antigens.

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15
  • The ABO blood group is important in blood
    transfusions.
  • If the blood recipient has never been exposed to
    an antigen (A or B) and that antigen enters the
    body it will cause an immune reaction. This can
    cause death.

16
  • In emergency rooms when there isnt time to
    figure out the blood type of the patient, which
    type of blood will the patient receive? Type O
    because these blood cells have no A or B
    antigens. People with Type O blood are called
    universal donors.
  • Who is the universal recipient that can receive
    blood from any donor? Type AB.

17
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18
Chapter 14-2Human Chromosomes
19
  • Most genetic disorders are caused by mutations on
    autosomes, or non-sex chromosomes.
  • Examples include
  • Autosomal recessive disorders albinism, cystic
    fibrosis, Tay-Sachs disease
  • Autosomal dominant disorders most common form
    of dwarfism (achondroplasia) and
    Hypercholesterolemia (high cholesterol)
  • Codominant disorders sickle-cell disease

20
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21
Albinism
Achondroplasia
22
  • Some genetic disorders are caused be genes on
    the sex chromosomes.
  • Most of these genes are on the X chromosome
    because the Y chromosome is very small and has
    few genes. The genes on X chromosome are
    different from the genes on the Y chromosome.

23
  • Because females are XX they have two copies of
    the genes on the X chromosome. For sex-linked
    traits, females can be homozygous dominant,
    heterozygous, or homozygous recessive.

24
  • Because males are XY they have only one copy of
    the genes on the X chromosome this is called
    hemizygous. In males, only one recessive allele
    on the X chromosome is necessary for the
    recessive phenotype to be expressed because there
    is not another allele for this gene on the Y
    chromosome. Some sex-linked (also known as
    X-linked) genetic conditions include
  • Color blindness- the inability to distinguish
    certain colors
  • Hemophilia- missing protein important for blood
    clotting
  • Duchenne Muscular Dystrophy- progressive
    weakening of skeletal muscles

25
Colorblindness- Test A
Everyone should be able to see a circle, star,
and square in the demonstration picture.
26
Colorblindness- Test B
Colorblind individuals should see the yellow
square. Color normal individuals should see the
yellow square and a "faint" brown circle.
27
Colorblindness- Test C
Colorblind individuals should see nothing. Color
normal individuals should see a "faint" brown
boat.
28
  • Example of a sex-linked Punnett square
  • XBXb (heterozygous female with normal vision)
    crossed to XBY (hemizygous male with normal
    vision)

XBY
Y
XB
XB XB
XBY
XB
XB Xb
XbY
XB Xb
Xb
29
Chromosomal Disorders
  • Remember that meiosis is the reductional cell
    division that divides one diploid cell to produce
    four haploid gametes (sex cells, sperm or egg).
    Normally gametes have one copy of each
    chromosome.
  • Sometimes chromosomes might not separate properly
    during meiosis this is called nondisjunction.
  • If nondisjunction occurs, abnormal numbers of
    chromosomes (usually one is missing or there is
    an extra copy of one) are found in gametes and
    disorders of chromosomal numbers may result.

30
gametes
31
  1. Trisomy Some chromosomal disorders are caused
    by having three copies of one chromosome. This
    is called trisomy. In trisomies, the gamete of
    one parent donated two of one type of chromosome
    to the child and the gamete of the other parent
    donated one chromosome (like normal).
  2. Monosomy Chromosomal disorders characterized by
    missing one chromosome are called monosomies. In
    monosomies, the gamete of one parent donated one
    chromosome and the other did not donate any.

32
  • Some examples of chromosomal disorders resulting
    from nondisjunction
  • Down syndrome- Trisomy 21
  • Klinefelters syndrome- XXY (male)
  • Turners syndrome- XO (female)
  • Add to your notes
  • As long there is at least one Y chromsome, the
    karyotype is male.

33
Human Genome Project
  • The human genome project sequenced the human
    genome. Now the code is being analyzed and
    scientists are finding genes for many traits and
    genetic disorders. In gene therapy, a gene that
    has been mutated and does not work properly is
    replaced by a normal, working copy of the gene.
    Gene therapy is a work in progress.
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