Biology Ch. 14 Human Heredity

I. Human Chromosomes - heredity in humans is the same as in other organisms - most genetic diseases are recessive and rare

A. Karyotype - A chart showing a complete diploid set of paired homologous chromosomes

1. Sex Chromosomes - pair of chromosomes that determine an individual’s sex XX - female XY – male - other sex determination systems exist

2. Autosomes - the other chromosome pairs except the sex chromosomes - Humans have _____ autosomes.

B. Inheritance of Human Traits 1. Dominant and Recessive Alleles - Many human traits are controlled by dominant and recessives alleles. - Ex. MC1R gene helps determine skin and hair color. Red hair results from being homozygous recessive for the MC1R gene.

2. Codominance - Both alleles are expressed in heterozygotes. - Ex. Type AB blood express IA and IB alleles. Type A Type AB Type B Type O

3. Sex-linked Traits - Traits controlled by genes located on the X sex chromosome. - Ex. Red-green colorblindness What People with Regular Vision See What Red-Green Colorblind People See

3. Sex-linked Traits - Traits controlled by genes located on the X sex chromosome. - Ex. Red-green colorblindness - Ex. Hemophilia

Queen Victoria’s Family

Pedigree of Europe’s Royal Families

4. X-Chromosome Inactivation - In females, 1 X chromosome is inactivated resulting in a mosaic of gene expression in heterozygotes - Ex. Calico cat

4. X-Chromosome Inactivation - In females, 1 X chromosome is inactivated resulting in a mosaic of gene expression in heterozygotes - Ex. Sweat gland mosaic Fertilized Egg Early Cell Division X Chromosome Inactivation Mitosis Maternal X Paternal X Barr Body Skin lacking sweat glands Normal skin

C. Pedigrees - A chart used to show inheritance patterns Pedigree chart of Queen Victoria’s family showing the inheritance of hemophilia.

II. Human Genetic Disorders - A mutation in DNA’s base sequence changes a protein’s structure by changing the sequence of amino acids. A single amino acid substitution in a protein causes sickle-cell disease.

A. Genetic Disorders Caused by Single Genes 1. Sickle-Cell Disease - affects hemoglobin, the protein that carries O2 in red blood cells - causes blood blockages, pain, tissue and organ damage

HbS Alelle Frequency(%) - most common in sub-Saharan Africa. - 1 out of 10 African-Americans are carriers. - Heterozygous advantage: carriers are resistant to malaria. Malaria HbS Alelle Frequency(%) > 12.5 10-12.5 7.5-10 5.0-7.5 2.5-5.0 0-2.5

2. Cystic Fibrosis (CF) - affects CFTR, a transport protein in the cell membrane - causes excessive production of thick mucus in lungs and digestive system

3. Huntington’s Disease - rare, dominant, nervous system disorder - symptoms (uncontrollable movements, mental deterioration) appear late in life Huntington’s Disease Woody Guthrie

B. Chromosomal Disorders Nondisjunction: - a failure of homologous chromosomes to separate during meiosis - results in gametes with missing or extra chromosomes

B. Chromosomal Disorders Nondisjunction:

Down Syndrome (Trisomy 21)

Incidence of Down Syndrome 10 20 30 40 50 100 200 300 400 Age of Mother (years) Number per 1000 Births

Turner’s Syndrome (Monosomy X)

XYY Syndrome

Trisomy X (XXX)

Klinefelter’s Syndrome (XXY)

Down Syndrome (Trisomy 21)

Normal Female

Edward’s Syndrome (Trisomy 18)

III. Selective Breeding - Humans have used selective breeding for thousands of years to produce new varieties of crops and domestic animals. Maize was domesticated from its wild grass ancestor more than 8,700 years ago.

III. Selective Breeding - Humans have used selective breeding for thousands of years to produce new varieties of crops and domestic animals. The dog was domesticated from the grey wolf over than 14,700 years ago.

A. Hybridization Nondisjunction: - a failure of homologous chromosomes to separate during meiosis - results in gametes with missing or extra chromosomes

B. Inbreeding Nondisjunction: - a failure of homologous chromosomes to separate during meiosis - results in gametes with missing or extra chromosomes

C. Polyploidy Nondisjunction: - a failure of homologous chromosomes to separate during meiosis - results in gametes with missing or extra chromosomes

The End

Human Chromosomes (23 homologous pairs)

Epistasis: Black, Chocolate, and Golden Labrador Retrievers