Chapter 14 – Human Genome

1. Chapter 14 – Human Genome

2. Human Chromosomes • Karyotype – arrangement of chromosomes in their homologous pairs and by length • Humans – 23 pair • 22 pair of autosomes • 1 pair of sex chromosomes

3. Pedigree • Graphic representation of genetic inheritance • Circle = female: square = male • Shaded = have trait; not shaded = do not have trait • Most recent generation at bottom • Generations identified by Roman numerals • Individuals identified by Arabic numbers (1,2,…)

4. Simple Recessive Heredity • Most genetic disorders are caused by recessive alleles • Albinism • Cystic fibrosis (CF) • 1 in 20 – carrier; 1 in 2000 – have it • Defective protein in plasma membrane results in formation and accumulation of thick mucus in lungs and digestive tract • Most common disorder among white Americans

5. Simple Recessive cont. • Tay-Sachs disease • Fatal disorder of central nervous system • Lipid build up on brain • Most common in US among Amish • Phenylketonuria (PKU) • Absence of enzyme that converts certain amino acids • Damage to CNS, mental retardation • Most common among people with ancestors from Norway and Sweden

6. Simple Dominant Heredity • Simple Dominant Traits • Tongue rolling, Hapsburg lip, earlobe types, hitchhiker’s thumb, almond eyes, thick lips, hair on middle of fingers • Huntington’s disease • Rare, lethal • Breakdown of brain • Onset between ages of 30-50 • Achondroplasia - dwarfism

7. Codominance in humans • Sickle-cell anemia • Twisted, bent (sickle-shaped) red blood cells • Cells are not able to carry oxygen normally, blood blow slows, blockage of smaller vessels, shorter life span for cells • Produces physical weakness and damage to heart and brain • Most common in African Americans • 1 out of 12 are heterozygous – produce normal and sickle

8. Multiple Alleles in humans • Blood groups – ABO groups and Rh group • Rh – single gene with 2 alleles – positive and negative • ABO groups • Determined by presence or absence of certain molecules on surface of red blood cell • Types : A, B, AB, O • Genes : IA, IB, i • Used to determine parentage • Ex. Child AB, mom A, man w/ O can not be father

9. Transfusions – need to know type to determine compatibility • A – IAIA, IAi • Can get from A or O • Can give to A or AB • B – IBIB, IBi • Can get from B or O • Can give to B or AB • AB – IAIB • Can get from A, B, AB, or O – universal recipient • Can give to AB • O – ii • Can get from O • Can give to A, B, AB, or O – universal donor

10. Sex-linked traits • Genes are found on the X or Y chromosomes • Colorblindness – most common red-green (found in 1/10 males in US) • Recessive on X chromosome • XBXB, XBXb – normal female • XbXb – colorblind female • XBY – normal male • XbY – colorblind male • Hemophilia – blood does not clot – may bleed to death from minor cuts • 1/10,000 males have • 1/1 million females have • Recessive on X chromosome

11. Calico cats • X chromosome may carry either black alleles or orange alleles • Females may have spots of both colors – 2 X chromosomes • Males only have one X chromosome so they will have black spots or orange spots but not both

12. Changes in chromosome # • Nondisjunction (homologous pairs do not split) occurs resulting in unusual numbers of autosomes – normal is 22 pair • Trisomy – have 3 of a certain autosome instead of 2 – results in 47 chromosomes • Ex. Down syndrome – trisomy of chromosome 21 – occurs 1/800 births

13. Changes in # cont. • Unusual numbers of sex chromosomes • Turner’s syndrome – females • Have only 1 X chromosome • Are sterile, sex organs may not develop • Klinefelter’s syndrome – males • Have an extra X – XXY • Usually sterile

14. Applications • Human DNA Analysis • Used to test for genetic disorders • DNA fingerprinting – used to identify individuals • Human Genome Project • Mapped the human DNA strand • Gene therapy – an absent or faulty gene is replaced by a normal, working gene • Still working on perfecting the practice