Human Genetics

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Transcript Human Genetics

Human Genetics
Human Genetics
I. Mutations= changes in DNA
a. Germ Cell Mutations–
occurs during meiosis;
takes place in sex cells
b. Somatic Mutations take place in the body cells
c. Mutations increase the
amount of variation among
II. Gene Mutation=Changes in Nucleotides of DNA
a. Point Mutations (2 types)
1.Base –pair substitutes:
may have no effect,
change amino acid;
or change to stop codon
2.Frameshift Mutations
• Base-pair insertion
or deletion
• Result is a
• Alters the reading
frame of mRNA
III. Chromosome Mutations
Deletion: removal of a chromosomal segment
Duplication: repeats a chromosomal segment
Inversion: segment reversal in a chromosome
Translocation: movement of a chromosomal segment to
another non-homologous chromosome
IV. Causes of Mutations
A. Chance
B. Mutagen = environmental factor damages DNA
Ex. UV light (sun; skin cancer), cigarette tar,
asbestos, virus, radiation
V. Karyotypes
A. Shows chromosomes
paired by size, shape,
and appearance in
B. Cells are treated,
photographed, sorted
and arranged by
homologous pairs.
C. Chorionic villi sampling,
and amniocentesis can
be used to diagnose
VI. Changing Chromosome Number
A. Nondisjunction =
failure of chromosomes
to separate during
Prophase I of
meiosis;addition or loss
of a chromosome
B. Monosomy occurs
when only one of a pair
is present (45)
C. Trisomy occurs when
three of a particular
type of chromosome is
present (47)
D. Nondisjunction Abnormalities
Many trisomies and nearly all monosomies are
XYY males (Jacob syndrome)- tall, acne, not
overly aggressive
XO females (Turner syndrome)- short, webbed
neck, no puberty.
Turner syndrome affects approximately 1 out of every
2,500 female live births worldwide. It embraces a broad
spectrum of features, from major heart defects to minor
cosmetic issues. Some individuals with Turner syndrome
may have only a few features, while others may have
many. Almost all people with Turner syndrome have short
stature and loss of ovarian function, but the severity of
these problems varies considerably amongst individuals.
E. Trisomy = Extra chromosomes (47)
1. Klinefelter Syndrome = XXY; male, some retardation,
low fertility (rare cases (48,XXXY) or (49,XXXXY)
2. Triple X Female (XXX) – no physical abnormalities
3. Fragile X Syndrome – X chromosome broken; males;
hyperactive or autistic, delayed speech
4. Down Syndrome = extra 21st chromosome; mental
retardation, fold of skin above eyes, weak muscles
VII. Sex Determination
A. A. Thomas Hunt Morgan
Experiments with
Drosophila (fruit fly)
Sex Chromosomes
Determine Gender
B. B. Autosomes are non-sex
C. (22 pairs)
D. C. Sex chromosomes
differ between males and
Human female is XX
Human male is XY.
D. Sex chromosomes carry genes for traits
unrelated to sex.
E. Single, recessive allele on X expressed
F. Males express sex-linked alleles more
G. Example of Sex Link Traits
Color Blindness
Hemophilia – blood doesn’t clot
x H x h = normal
x Hy = normal
x x = normal
x h y = hemopheilia
XhXh = hemophilia
VIII. Human Genetics Traits
A. Single Allele Traits
1. Sickle Cell Anemia
a. Sickle shaped red cells
b. Clump; block arteries, lack 02,
pain, weakness, death
c. AA= normal cell
AA’= both kinds; protected from
A’A’= sickle cells
2. Huntington’s Disease
Cause by one dominant allele
Brain cells degenerate; no muscle control; death
Occurs at 30 -40; passed to child 50% of time
3. Tays-Sacs, Cystic Fibrosis,
Tays Sachs Disease is an inherited incurable disease of the central nervous system.
Its symptoms first appear when a baby is about 6 months old. The baby stops smiling and
developing through the normal developmental stages. Blindness and paralysis follow within
the next four years resulting in the child's death by the age of five years. Most babies die
within the first two years.
B. Polygenic Traits
= 2 or more genes control trait
1.Skin color - 4-7 genes with additive effect of amount
of melanin
2. Eye Color – blue (light melanin), brown (lot of
3. Height
C. Multiple Allele Traits
= Trait with 3 or more alleles; only get 2
1. ABO Blood group system; types – A, B, AB, O
2. AA =type A AO = type A
OO = type O
BB= type B BO = type B AB= type AB
*A,B codominant
*Both dominant to O
D. Sex Influenced Traits
= not a sex chromosomes; influenced by sex hormones
B=Baldness; dominant in males and
recessive in females
BB=bald females and males
BB” – female will not lose her hair
BB” – male will lose hair
IX. Studying Humans
A. Population Sampling =
select a number to represent
whole population
B. Twin Studies –
environment vs. genetics
C. Pedigree Studies –
family chart of traits
D. DNA fingerprinting = study the
patterns of bands obtained
from electrophoresis
1. Gel electrophoresis –
process to separate DNA
fragments by size of charge
IN: P 34
Contrast 2 types of point mutations.
OUT: P34
Mutations occur at 2 levels. What are they?
IN: P 36
A new species has been discovered.
The organism has 18 chromosomes.
How many chromosomes would the
new species have if a monosomy
occurred? …a trisomy?
OUT: P36
Hemophilia is a sex linked disease.
Cross a normal male with a female that
is a carrier of the disease. What percent
of the males will have hemophilia?
IN: P 38
What do you know about sickle cell
Explain polygenic traits in your own
words. How would an albino occur?