Understanding Human Genetics: Multiple Alleles, Sex-Linked Traits, and Genetic Disorders

1. Human Genetics

2. Multiple Alleles • There are more than two possible genes that can be inherited for a trait. • Examples • Flower color • Blood type

3. Sex-linked Traits • Trait for which the gene is located on one of the sex chromosomes. XHXH ~ female, normal XHXh ~ female, normal carrier XhXh ~ female, hemophiliac XHY ~ male, normal XhY ~ male, hemophiliac

4. Pedigrees • A family tree that shows how a particular trait is passed from parents to offspring. • Be able to read and interpret

5. Pedigree of a Sex-linked Trait Colorblindness is sex-linked. Blue box is colorblind White box is normal vision with two normal genes. Half blue/half white is a carrier with normal vision, but one abnormal gene.

7. Karyotypes • Process in which cells undergoing mitosis are crushed, and their chromosomes paired up. This can reveal abnormalities as seen below. Female – 2 X chromosomes

8. Nondisjunction • The failure of chromosomes to separate during anaphase I or II of meiosis. • Can result in too many chromosomes (Down Syndrome) or not enough (Turner Syndrome)

9. Autosomal Dominant Diseases • If the abnormal gene is present, the person has the disease • Huntington’s Disease

10. Huntington’s Disease • Chromosome 4 • HH or Hh • Nerve cells degenerate • Symptoms include: mood swings, irritability, loss of memory, and uncontrolled movements • People of western European descent

11. Autosomal Recessive disease • Must have 2 abnormal forms of the gene for the disease to be present • Cystic Fibrosis • Tay Sachs • PKU (Phenylketonuria) • Sickle Cell Anemia

12. Cystic Fibrosis • Chromosome 7 • cc • Causes think, sticky mucus to build up in the lungs, digestive tract, and other areas of the body • Mainly Caucasians

13. Tay Sachs • Chromosome 15 • tt • Causes a buildup of a chemical on the nerve cells • Babies lose or fail to gain motor and mental skills • Paralysis usually occurs • Death at an early age • Jews of eastern European descent and French-Canadians

14. PKU • Chromosome 12 • pp • Born without the ability to break down phenylalanine • Smaller than normal head, epilepsy, and mental retardation may occur when undiagnosed • Caucasians and east Asians

15. Sickle Cell Anemia • Chromosome 11 • ss • Red blood cells form an abnormal crescent shape • Pain; spleen, lung, and heart damage, and anemia • People of African descent

16. Sex-linked Diseases • Gene for the disease is carried on the sex-chromosome • Colorblindness • Hemophilia

17. Colorblindness • Carried on the X chromosome • XbXb or XbY • Cannot distinguish between colors • Affects all races and ethnic groups

18. Hemophilia • Carried on the X chromosome • XhXh or XhY • Blood does not clot well because missing the gene that codes for a blood clotting protein • Affects all races and ethnic groups

19. Chromosomal Aneuploidy Diseases • A disease caused by an abnormal number of chromosomes • Down Syndrome • Turner’s syndrome • Kleinfelter’s syndrome • XYY Male

20. Down’s Syndrome • Autosomalanueploidy • Trisomy (three chromosomes at 21) • Mental retardation, upward slant to the eyes, decreased muscle tone, and a variation of other symptoms

21. Turner’s Syndrome • Sex chromosome anueploidy • Monosomy • Alters development in females; shorter than average, infertile, extra skin on the neck, skeletal abnormalities, heart defects, and kidney problems

22. Kleinfelter’s Syndrome • Sex chromosome anueploidy • Trisomy (XXY) • Armpit and facial hair, enlarged breasts, tall stature, and abnormal body proportions • Increased possibility of learning disorders

23. XYY Male • Sex chromosome anueploidy • Trisomy (XYY) • Increased risk of learning disabilities, delayed speech and language skills