Download BIO 103 More Genetics Ch.13

Chromosomes, Mapping, and the
Meiosis-Inheritance Connection
Chapter 13
I. Introduction
A.46 chromosomes in each
cell (23 pairs)
B.Autosomes: all
chromosomes except sex
chromosomes (22 pairs)
C.Sex chromosomes:
determine gender (1 pair)
1.Sex determination
a)XX = female
b)XY = male
2.During meiosis, each egg from
the female gets an X; 1/2 male
sperm get X, 1/2 get Y
3.Males determine gender of
offspring!
a)Except in birds and reptiles
where female is XY and male
is XX
II. Studying human genetics
A.Difficult because
1. Long generations (25 yrs)
2. Single births
3. Ethical concerns
B.Methods for studying humans
1.Pedigrees: record that shows
how a trait is inherited within a
family
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2. Population sampling
1. Selecting a small # of people to
represent an entire population
2. Must be a random sample
3. Ex: through random sampling,
researchers discovered that 65% of
people in US taste PTC, 35%
cannot
3. Identical twin studies
a) Identical genetic codes
b)Separated at birth: study which
traits are genetic(Nature) & which
are environmental (Nurture)
Human Genetic Disorders
Some human genetic disorders are caused
by altered proteins.
the altered protein is encoded by a mutated
DNA sequence
the altered protein does not function
correctly, causing a change to the
phenotype
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III. Inheritance of human traits
A. Dominant traits
1. Polydactyly - extra fingers &
toes
2. Dwarfism - small size
3. Curly hair
4. Huntington disease - nervous
disorder
5. Piebaldness - white patches of
hair
Piebaldness=Genetic
Vitiligo=AutoImmune
B.Recessive traits
1.Straight hair
2.Freckles
3.Albino
4.Cystic fibrosis - lung disorder
5.Deafness
6.PKU - nervous disorder
Odds of having
a child with the
disease?
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C.Codominance
1.Sickle cell anemia - irregularly
shaped red blood cells
• O allele = healthy(HH)
• 1 allele = mild case(HS),
resistant to malaria
• 2 alleles =
severe case(SS)
Sex Chromosomes
In each female cell, 1 X chromosome is
inactivated and is highly condensed into a
Barr body.
Females heterozygous for genes on the X
chromosome are genetic mosaics.
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F. Sex-linked traits
1. Genes located on X chromosome
2. Males only have one X, so only
have one allele controlling these
genes
3. Males more likely to have disorders
that are sex-linked because they
only need 1 recessive allele
4. Carrier: someone who has one
allele for a disorder -- does not
have the disease but can pass it
on to children
5. Only women can be carriers for
sex-linked traits
6. Examples: hemophilia, muscular
dystrophy, colorblindness
Hemophilia in the
Royal Families of Europe
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7. Color vision
a) XC=Color Vision, Xc=colorblind
b) Males - 8% colorblind (XcY)
c) Females - 1% colorblind (XcXc)
Red-Green
Total
Normal
What are the chances for a healthy
dad and a mom who is a carrier for
colorblindness to have a child that
is colorblind?
IV. Genetic disorders
A. Nondisjunction: failure of
chromosomes to separate during
meiosis
1. Normal = 23 chromosomes
2. Abnormal = 22 or 24
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3. Monosomy: too few chromosomes,
one chromosome left unpaired
a) Turner syndrome: female with
only 1 X chromosome
b)Short stature, sterile
4. Trisomy: too many chromosomes,
extra copy of one
a) Down’s syndrome: trisomy 21
b)1 in 1400 when mother under age
25, 1 in 100 by age 40
Human Genetic Disorders
Nondisjunction of sex chromosomes can
result in:
XXX triple-X females
XXY males (Klinefelter syndrome)
XO females (Turner syndrome)
OY nonviable zygotes
XYY males (Jacob syndrome)
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B.Detecting genetic disorders
1. Physical characteristics - features,
disabilities
2. Ultrasound - pictures of baby in
utero using sound waves
3. Amniocentesis - sample of fluid from
around baby, can examine baby’s
cells
http://www.biology.iupui.edu/biocourses/n100/2k4csomaldisordersnotes.html
http://www.katie.com/babyblog/archives/000538.html
http://www.katie.com/babyblog/archives/000538.html
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4.Karyotype: picture of a person’s
cromosomes
• taken from any cells -- blood
in adults, amnio for baby
Normal
Trisomy 21
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