Chromosomes and Human Genetic Disorders 1 In Chapter 13 you are not responsible for: Section 13.4 (genetic mapping) Genomic imprinting (in section 13.5)

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

Chromosomes and Human Genetic Disorders

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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

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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)