Chromosomes and Human Genetic Disorders
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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
Chromosomes and Inheritance -- Chapter 13
G-banding patterns for human chromosomes
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What is a Karyotype?
How is a karyotype prepared?
1. Collect & culture cells2. Treat with mitotic inhibitor3. Spread out cells and stain4. Photograph & pair up chromosomes
Chronic myeloid leukemiaA 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
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What is unusual about the inheritance of hemophilia?
The Romanov familyCzar Nicholas and Alexandra
Rasputin
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Ishihara test
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 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
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How do chromosomal abnormalities affect traits?
Changes in DNA code alterprotein structure
Sickle cell anemia redux…
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How do chromosomal abnormalities affect traits?
Nondisjunction and aneuploidy
Autosomal aneuplopidye.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)
Nondisjunction
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Other examples of human aneuploidy
Edwards Syndrome (Trisomy 13)
Patau Syndrome (Trisomy 13)