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) Genetic test – we’ll cover this later Chromosomes and Inheritance -- Chapter 13 G-banding patterns for human chromosomes

Chromosomes and Human Genetic Disorders 2 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 3 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 4 What is unusual about the inheritance of hemophilia? The Romanov family Czar Nicholas and Alexandra Rasputin

Chromosomes and Human Genetic Disorders 5 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 X C = normal allele X c = recessive abnormal Question Color responsiveness of different types of cone cells

Chromosomes and Human Genetic Disorders 6 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) GenotypeMalesFemales Homozygous recessive normal Heterozygousbaldingthinning Homozygous dominant baldingbalding (less so) Image ©

Chromosomes and Human Genetic Disorders 7 How do chromosomal abnormalities affect traits? Changes in DNA code alter protein structure Sickle cell anemia redux…

Chromosomes and Human Genetic Disorders 8 How do chromosomal abnormalities affect traits? Nondisjunction and aneuploidy 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) Nondisjunction

Chromosomes and Human Genetic Disorders 9 Other examples of human aneuploidy Edwards Syndrome (Trisomy 13) Patau Syndrome (Trisomy 13)