Download Chapter 13

Chromosomes and Inheritance
-- Chapter 13
In Chapter 13 you are
not responsible for:
Section 13.4 (genetic mapping)
Genomic imprinting (in section 13.5)
Genetic test – we’ll cover this later
G-banding patterns for
human chromosomes
Chromosomes and Human
Genetic Disorders
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What is a Karyotype?
How is a karyotype prepared?
1. Collect & culture cells
2. Treat with mitotic inhibitor
3. Spread out cells and stain
4. Photograph & pair up chromosomes
Chronic myeloid leukemia
A reciprocal chromosome translocation has
occurred between Chromosomes 9 & 22
Chromosomes and Human
Genetic Disorders
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How is sex determined?
Different organisms have different
Mechanisms
insects
reptiles
mammals
Does egg or sperm determine the sex
of the offspring?
What genes are on the sex chromosomes?
-- > 1000 on X; many different functions
-- < 100 on the Y
Why does Y chromosome contain few genes?
Study ‘X chromosome inactivation’ in the textbook
Chromosomes and Human
Genetic Disorders
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What is unusual about
the inheritance of hemophilia?
The Romanov family
Czar Nicholas and Alexandra
Chromosomes and Human
Genetic Disorders
Rasputin
4
Genes on the X chromosome are
said to be ‘sex linked’
Abnormal genes often act as dominants
in males and recessive in females. Why?
Designation of X-linked genes
What is the theoretical frequency of hemophilia among
the children of a normal father and a carrier mother?
… From a hemophiliac mother?
Red-Green Color Blindness
~10% of males; <1% of females
XC = normal allele
Xc = recessive abnormal
Question
Ishihara test
Chromosomes and Human
Genetic Disorders
Color responsiveness of
different types of cone cells
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What causes a “sex-influenced” trait?
Gene is autosomal
Expression influenced by sex
-- hormonal or genetic factors
e.g., pattern baldness
voice (baritone vs mezzo-saprano)
Genotype
Males
Females
Homozygous
recessive
normal
normal
Heterozygous
balding
thinning
Homozygous
dominant
balding
balding (less so)
Image © http://www.revolutionhealth.com
Chromosomes and Human
Genetic Disorders
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How do chromosomal
abnormalities affect traits?
Changes in DNA code alter
protein structure
Sickle cell anemia redux…
Chromosomes and Human
Genetic Disorders
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How do chromosomal
abnormalities affect traits?
Nondisjunction and aneuploidy
Nondisjunction
Autosomal aneuplopidy
e.g., Down’s syndrome (trisomy 21)
-- non-disjunction of chromosomes
Sex-chromosome aneuploids
X-chromosome nondisjunction
-- XO (Turner syndrome)
-- XXY (Klinefelter syndrome)
Y-chromosome nondisjunction
-- XYY (read about in text)
Chromosomes and Human
Genetic Disorders
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Other examples of
human aneuploidy
Edwards Syndrome
(Trisomy 13)
Patau Syndrome
(Trisomy 13)
Chromosomes and Human
Genetic Disorders
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