Chromosomes and Human Inheritance - Patterns of Inheritance

1. Chromosomes and Human Inheritance - Patterns of Inheritance

2. Independent Assortment • Mendel’s Law of Independent Assortment only works for genes whose loci are on different chromosomes

4. Genes on Same Chromosome • Linked genes

5. Genes on Same Chromosome • Example of genetic linkage • Flower color and pollen shape are on same chromosome in sweet peas • Gene assignments • Let P = purple flowers and p = red flowers • Let L = long pollen shape and l = round shape

7. Recombination • Genes on same chromosome do not always sort together • Crossing over in Prophase I of meiosis creates new gene combinations • Crossing over involves the exchange of DNA between chromatids of paired homologous chromosomes

8. Sex Chromosomes and Autosomes • Autosomes • Sex Chromosomes • XX (x) XY

9. Sex-Linked Genes • Genes carried on one sex chromosome are sex-linked • X and Y chromosomes have very few genes in common

10. How Sex-Linkage Affects Inheritance • Eye color genes were found to be carried by the X chromosome • R = red eyes (dominant) • r = white eyes (recessive) http://www.taxodros.uzh.ch/

11. How Sex-Linkage Affects Inheritance • Sex-linked (specifically X-linked) recessive alleles displayed their phenotype more often in males • Males showed recessive white-eyed phenotype more often than females in an XRXrxXRY cross

12. Incomplete Dominance • Incomplete Dominance • When the heterozygous phenotype is intermediate between the two homozygous phenotypes

14. Multiple Alleles • A species may have more than 2alleles for a given characteristic • Each individual still carries 2alleles for this characteristic • Ex. Fruit fly eye color • Ex. A, B, O blood type

15. Codominance • Heterozygotes display phenotypes of both the homozygote phenotypes in codominance • Example: Human blood group alleles

16. Polygenic Inheritance • Are governed by the interaction of more than 2 genes at multiple loci • Examples include human height, skin color, and body build, and grain color in wheat

18. Epigenetics • Environment can influence how genes are expressed • Example: Himalayan rabbit

21. Recessive Genetic Disorders • New alleles produced by mutation usually code for non-functional proteins • Alleles coding for non-functional proteins are recessive to those coding for functional ones

22. Recessive Genetic Disorders • Heterozygous individuals are carriersof a recessive genetic trait • (but otherwise have a normal phenotype) • Homozygous recessive genes express the defective phenotype

23. Albinism • Melanin is the dark pigment that colors skin cells • Melanin is produced by the enzyme tyrosinase (TYR) • Mutant TYR allele encodes a defective tyrosinase protein in skin cells, producing no melanin

24. Albinism • Humans and other mammals who are homozygous for the mutant TYRhave no skin, fur, or eye coloring (skin and hair appear white, eyes are pink)

25. Sickle-Cell Anemia • Hemoglobin- oxygen-transporting protein found in red blood cells • Mutant hemoglobin gene causes hemoglobin molecules in blood cells to clump together • Red blood cells take on a sickle (crescent) shape and easily break

28. Dominant Genetic Disorders • Dominant disease alleles disrupt normal cell function in a variety of ways • Produce an abnormal protein that interferes with the function of the normal one • Encode toxic proteins • Encode a protein that is overactive or active at inappropriate times and places

29. Sex-Linked Genetic Disorders • Several defective alleles for characteristics encoded on X chromosome • Sex-linked disorders appear more frequently in males and often skip generations • Ex. Red-green color blindness

31. Sex-Linked Genetic Disorders • Hemophilia (deficiency in blood clotting protein) • Hemophilia gene in Queen Victoria of England was passed among the royal families of Europe

33. Errors in Chromosome Number

34. Non-Disjunction • Incorrect separation of chromosomes or chromatids in meiosis known as non-disjunction

36. Abnormal Sex Chromosome Number • Non-disjunction of sex chromosomes in males or females produce abnormal numbers of X and Y chromosomes

37. Abnormal Sex Chromosome Number • Turner Syndrome (XO): an underdeveloped, infertile woman with only one X chromosome lucinafoundation.org

38. Abnormal Sex Chromosome Number • Trisomy X (XXX): a fertile, “normal” woman with an extra X chromosome

39. Abnormal Sex Chromosome Number • Kleinfelter Syndrome (XXY): an infertile man with an extra X chromosome, having partial breast development and small testes beliefnet.com

40. Abnormal Sex Chromosome Number • Jacob Syndrome, • XYY Male: a tall man with an extra Y that produces high levels of testosterone and may score lower on IQ tests biology.iupui.edu

41. Abnormal Autosome Number • Non-disjunction of autosomes can occur during meiosis in the father or mother • Frequency increases with age of parents

42. Abnormal Autosome Number • Trisomy 21 (Down Syndrome) • Individuals have 3copies of chromosome 21 • Characterized by distinctively shaped eyelids, among other physical features

44. The End