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Fundamentals of human genetics. Methods of research of human heredity.

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Fundamentals of human genetics. Methods of research of human heredity. Ass. Nedoshytko Khrystyna Royal Hemophilia Pedigree Duchenne Muscular Dystrophy Duchenne ... – PowerPoint PPT presentation

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Title: Fundamentals of human genetics. Methods of research of human heredity.


1
Fundamentals of human genetics. Methods of
research of human heredity.
Ass. Nedoshytko Khrystyna
2
Genetic Terminology
  • Genotype- the alleles a person has
  • Phenotype- the observable trait a person has
  • Dominant- Alleles affect masks the other allele
    it is paired with
  • Recessive- Alleles affect is masked by the other
    allele it is paired with.
  • Homozygous- Pair of alleles for a trait are
    identical
  • Heterozygous- Pair of alleles for a trait are not
    identical
  • Hybrid- Inherit non-identical alleles for a trait

3
VISUAL REPRESENTATION Pair of Chromosomes Gene Lo
cus (loci) Alleles Heterozygous Homozygous
A pair of homologous chromosomes, each in the
unduplicated state (most often, one from a male
parent and its partner from a female parent)
Heterozygous
Homozygous
A gene locus (plural, loci), the location for a
specific gene on a specific type of chromosome
A pair of alleles (each being a certain
molecular form of a gene) at corresponding loci
on a pair of homologous chromosomes
Three pairs of genes (at three loci on this pair
of homologous chromosomes) same thing as three
pairs of alleles
4
Homologous Chromosomes
  • Homologous autosomes are identical in length,
    size, shape, and gene sequence
  • Sex chromosomes are nonidentical but still
    homologous
  • Homologous chromosomes interact, then segregate
    from one another during meiosis

DNA
DNA and proteins arranged as cylindrical fiber
Nucleosome
Histone
5
Human Karyotype
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
17 18 19 20
21 22 XX (or XY)
6
Karyotype Preparation
  • Cultured cells for 3 to 4 days in the presence of
    phytohaemagglutinin (mitogen) and arrested at
    metaphase
  • This is when cells are most condensed and easiest
    to identify Arrested cells are broken open
  • Metaphase chromosomes are fixed and stained (how
    many copies of each chromosome in one cell?)
  • Chromosomes are photographed through microscope
  • Photograph of chromosomes is cut up and arranged
    to form a karyotype diagram

7
  • Karyotypes
  • The Alaskan king crab has 208 chromosomes.
  • The fruit fly has 4.
  • Number has nothing to do with complexity of the
    organism

Cotton Rat (Sigmodon hipsidus)
Pied Kingfisher (Ceryle rudis)
Carrion Beetle (Phosphuga atrata)
8
Prenatal Diagnosis
  • Amniocentesis (1-2)
  • Amniotic fluid removed
  • Chorionic villus sampling (0.3)
  • Cells from the chorion (surrounds ammnion)
  • Fetoscopy (2-10)
  • Direct visualization, removal of blood from
    umbilical vein

9
Prenatal diagnosis
www.visembryo.com/baby/hp.html
10
Amniocentesis
Removal of about 20 ml of amniotic fluid
containing suspended cells that were sloughed off
from the fetus Performed during weeks 15-17 of
pregnancy
A few biochemical analyses with some of the
amniotic fluid
Centrifugation
Quick determination of fetal sex and analysis of
purified DNA
Fetal cells
Biochemical analysis for the presence of alleles
that cause many different metabolic disorders
Growth for weeks in culture medium
Fig. 11.19, p. 186
Karyotype analysis
11
Sex Chromosomes
  • Discovered in late 1800s
  • Mammals, fruit flies
  • XX is female, XY is male
  • Human X and Y chromosomes function as homologues
    during meiosis
  • (In some organisms XX is male, XY female but for
    this class XX is female and XY is male, no tricky
    stuff)

12
Sex Determination
eggs
sperm
Female germ cell
Male germ cell
sex chromosome combinations possible in new
individual
13
The Sex Chromosomes
  • The Y Chromosome
  • Fewer than two dozen genes identified
  • One is the master gene for male sex determination
  • SRY gene (Sex-determining region of Y)
  • SRY present, testes form
  • SRY absent, ovaries form
  • The X Chromosome
  • Carries more than 2,300 genes
  • Most genes deal with nonsexual traits
  • Genes on X chromosome can be expressed in both
    males and females

14
Pedigree
  • Chart that shows genetic connections among
    individuals
  • Standardized symbols
  • Knowledge of probability and Mendelian patterns
    used to suggest basis of a trait
  • Conclusions most accurate when drawn from large
    number of pedigrees

15
  • The individual who needs genetical medical
    consultation is called the proband O,
  • Proband tells to doctor medical history about his
    disorder and any other affected persons in the
    family. If this disorder (disease) is
    inheritance, we can draw family trees.

16
Pedigree symbols
17
  • Children marked under horizontal line from left
    to right, in order of birth.
  • Members of the same generation are placed on the
    same horizontal level. Roman numbers are used for
    each generation and Arabic numerals are used to
    indicate each individual within a generation.

18
Pedigree for Polydactly
male
female

1
2
3
4
5
19
Autosomal Recessive Inheritance Patterns
  • If parents are both heterozygous, child will have
    a 25 chance of being affected

20
Galactosemia
  • Caused by autosomal recessive allele
  • Gene specifies a mutant enzyme in the pathway
    that breaks down lactose

enzyme 1
enzyme 2
enzyme 3
GALACTOSE-1- PHOSOPHATE
GALACTOSE-1- PHOSOPHATE
LACTOSE
GALACTOSE
glucose
intermediate in glycolysis
21
Autosomal Dominant Inheritance
  • Trait typically appears in every generation

22
Huntington Disorder
  • Autosomal dominant allele
  • Causes involuntary movements, nervous system
    deterioration, death
  • Symptoms dont usually show up until person is
    past age 30
  • People often pass allele on before they know they
    have it

23
Genetics Problem
  • A woman (hh) with normal nerve physiology has a
    child with a man (Hh) who will develop Huntington
    Disease
  • What is the chance that the child will have
    Huntington Disease?

24
Sex-Linked Genes
  • Is there a special pattern of inheritance for
    genes located on the X chromosome or the Y
    chromosome?
  • Because these chromosomes determine sex, genes
    located on them are said to be sex-linked genes
  • Many sex-linked genes are found on the X
    chromosome
  • More than 100 sex-linked genetic disorders have
    now been mapped to the X chromosome
  • The human Y chromosome is much smaller than the X
    chromosome and appears to contain only a few
    genes

25
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26
X-Linked Recessive Inheritance
  • Males show disorder more than females
  • Son cannot inherit disorder from his father

27
A typical X-linked recessive pedigree
28
X Linked Recessive Inheritance
  • Trait is much more common in males than females
  • An affected man passes the gene to all of his
    daughters
  • A son of a carrier mother has a 50 chance of
    inheriting the trait
  • Male-to-male transmission never occurs
  • Carrier females are usually asymptomatic, but
    some may express the condition with variable
    severity because of Lyonization, or
    X-inactivation.

29
X-Chromosome Inactivation
  • Females have two X chromosomes, but males have
    only one
  • If just one X chromosome is enough for cells in
    males, how does the cell adjust to the extra X
    chromosome in female cells?
  • The answer was discovered by the British
    geneticist Mary Lyon
  • In female cells, one X chromosome is randomly
    switched off
  • That turned-off chromosome forms a dense region
    in the nucleus known as a Barr body
  • Barr bodies are generally not found in males
    because their single X chromosome is still active

30
Barr body
31
X linked recessive, normal father, carrier mother
carrier daughter 1 normal daughter 1 affected
son 1 normal son
32
X linked recessive, affected father
  • 2 carrier daughters
  • 2 normal sons
  • Never any Male-to-
  • Male transmission!

33
Examples of X-Linked Traits
  • Color blindness
  • Inability to distinguish among some of all colors
  • Hemophilia
  • Blood-clotting disorder
  • 1/7,000 males has allele for hemophilia A
  • Was common in European royal families

34
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35
Royal Hemophilia Pedigree
36
Duchenne Muscular Dystrophy 
  • Duchenne muscular dystrophy is a sex-linked
    disorder that results in the progressive
    weakening and loss of skeletal muscle
  • In the United States, one out of every 3000 males
    is born with this condition
  • Duchenne muscular dystrophy is caused by a
    defective version of the gene that codes for a
    muscle protein
  • Researchers in many laboratories are trying to
    find a way to treat or cure this disorder,
    possibly by inserting a normal allele into the
    muscle cells of Duchenne muscular dystrophy
    patients

37
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38
Distribution of Mendelian disorders
  • 68 Autosomal dominant
  • 26 Autosomal recessive
  • 6 X-linked recessive

39
  • In a sex-influenced trait, an allele is dominant
    in one sex but recessive in the other.
  • Hormonal differences can cause this difference in
    expression.
  • For example, a gene for hair growth pattern has
    two alleles, one that produces hair all over the
    head and another that causes pattern baldness.
    The baldness allele is dominant (A) in males but
    recessive (a) in females, which is why more men
    than women are bald. A heterozygous male (Aa) is
    bald, but a heterozygous female is not. The
    genotype of a bald women is aa.

40
More Sex-Linked Recessive Inheritance
Male-pattern baldness
By age 50, nearly 60 of all men will experience
some male pattern baldness.

35 million Americans
experience some degree of hair
loss, resulting in 900 million dollars a year
being spent in efforts to grow it back.
Rogaine only 5 actually grow hair, 20-30 will
have no effect,
41
X-Linked Dominant inheritance 
1) a trait affects mostly females 2) if the
affected female is heterozygous, she will pass
the trait to a half of her offspring (male and
female) 3) an affected male passes the trait to
his daughters.
42
Enamel hypoplasia (hereditary defect that cause
holes and cracks to appear around the crowns of
the teeth) is sex-linked dominant trait.

43
Y-Linked inheritance
1)        a trait affects only males 2) father
passes a trait to all sons.
44
Hairy pinnae (hairy ears) Y-linked trait
45
Y-linked Ear-Hair
X X
X y
X X
X y
y Ear Hair
46
Thank you for attention !
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