1. The Human Genome
Chapter 14

2. 14-1 Human Chromosomes Are pictured in karyotypes 46 human chromosomes
pictures taken during metaphase
Cut out photos and place in correct order
46 human chromosomes
2 sex chromosomes
Females are XX
Males are XY
44 autosomes

3. Karyotype

4. Human gametes All eggs have one X chromosome ½ of all sperm carry an X
½ of all sperm carry a Y
*males determine gender of offspring*

5. Human traits Inherited by the laws of Mendelian genetics
Most traits are NOT simple dominant/recessive inheritance
Many traits influenced by environment
*environmental effects are NOT inherited; only genes are inherited*

6. Human traits Can be traced through a family using a pedigree
Individuals exhibiting the trait will be shaded
Individuals without the trait are blank
Males are square, females are round
Mates are connected by horizontal line

7. Pedigree – autosomal dominant

8. Pedigree – autosomal recessive

9. Pedigree – sex (X) linked

10. Human genes for blood
Rh factor is a single gene with 2 alleles; one + and one –
+ is dominant; - is recessive
Rh stands for rhesus monkey; the animal in which it was discovered

11. Human recessive traits
PKU (phenylketonuria)-inability to metabolize the amino acid phenylalanine
Results in buildup in nervous system causing retardation
Newborns are tested
Controlled by diet

12. Human recessive traits
Tay-sachs disease-nervous system break-down causing death before age 5
Found in Jewish families of European ancestry
No cure
Parents can be tested to determine risk

13. Recessive traits
Cystic fibrosis (CF)-results in serious digestive problems and excess mucus in the lungs
Found in people with ancestors from northern Europe

14. Human dominant traits Dwarfism (achondroplasia)
Huntington’s disease-progressive loss of muscle control and mental function until death occurs
No symptoms before age 30
No cure

15. Complex forms of inheritance
Multiple alleles
Codominance
Incomplete dominance
Polygenic traits

16. Human blood groups (multiple alleles)
3 alleles govern human blood types
IA, IB, and i produce antigens on the surface of the red blood cells
IAIA and IAi have A blood
IBIB and IBi have B blood
IAIB have AB blood (codominant)
ii have O blood (recessive)

17. Codominance
Black and white feather colors in chickens are equally dominant.

18. Codominance

19. 14-2 Human chromosomes
Linked genes are close together on the chromosomes; usually inherited together
Linked genes can be separated during crossing over during meiosis

20. Incomplete dominance
Two alleles governing a trait, but one does NOT completely dominate the other
Produces a blending pattern in the heterozygote

21. Incomplete dominance

22. Incomplete dominance

23. Polygenic traits Traits determined by a combination of genes
At least 3 genes are involved

24. Polygenic traits

25. Polygenic traits: epistasis
Multiple genes involved with fur color in mice and other animals
Some genes determine color
Some genes determine the shade of the color
Some genes determine spotting

26. Polygenic traits: epistasis

27. Sex-linked genes Genes located on the sex chromosomes
Many on X chromosome
Few on Y chromosome (Y is smaller)

28. Sex-linked traits Colorblindness Hemophilia
Duchenne Muscular Dystrophy

29. Colorblindness Three genes on X chromosome
Most common is red-green colorblindness
1 out of 10 males are affected
1 out of 100 females are affected
*occurs in males more often because of only 1 X chromosome*

30. Hemophilia Two genes on X chromosome
Affected individuals lack a blood-clotting protein
1 in 10,000 males are affected
Can be treated with injections of normal blood-clotting agents

31. Duchenne Muscular Dystrophy
Results in weakening and loss of skeletal muscle
1 in 3000 males affected in U.S.
Caused by defective protein

32. X-chromosome Inactivation
Males have 1 X chromosome
Females have 2 X chromosomes (one is non-functional)
Non-functional X becomes a Barr Body in the nucleus
X chromosomes in females are randomly switched off; in males the X is always active

33. Chromosomal disorders
Nondisjunction – chromosomes don’t separate properly in meiosis and some cells get abnormal numbers of chromosomes
Down’s syndrome
Turner’s syndrome
Klinefelter’s syndrome

34. Down’s Syndrome Autosomal disorder of chrom. 21 (trisomy)
1 in 800 babies in U.S.
Mild to severe learning disabilities
Increased health problems
Higher frequency of birth defects

35. Turner’s syndrome Females with only 1 X chromosome (45 chromosomes)
Sterile
Sex organs do not develop

36. Klinefelter’s syndrome
Males with an extra X chromosome (47 chromosomes)
sterile

37. 14-3 Human molecular genetics
DNA analysis
Used to determine possibility of passing genetic disorders to children
Use labeled DNA sequences to base pair to problematic complementary base sequences
Can pinpoint exact genetic basis of some disorders

38. DNA fingerprinting Used to identify individuals
Analyzes sections of DNA with little or no known function but vary widely between individuals

39. Human genome project Complete in 2000
Have determined entire DNA base sequences
Using those sequences to determine genes and their locations

40. Gene therapy
Replacing absent or faulty gene with the correct working gene
Body can make correct proteins
Still high-risk and experimental

41. Ethics in human genetics
Curing diseases is essential
Should we alter the outcomes of reproduction by altering natural genetics?
All citizens are responsible for the WISE use of the information gained in research.