Human Chromosomes Inheritance Autosomes (1-22) Homologous Chromosome Size & shape Centromere

1. Human Chromosomes • Inheritance • Autosomes (1-22) • Homologous Chromosome • Size & shape • Centromere • Staining pattern • genes • Sex Chromosomes X and Y • Non-homologous • Size and shape • Centromere • Staining pattern • Genes • Determine sex • XX = female • XY = male

2. X-Linked (Sex-Linked) Inheritance X Chromosome: Carries many important genes Color blindness Y Chromosome: Genes for sperm production. Different pattern of inheritance. • Y is blank: no genes/alleles • Y can’t cover recessive allele a_ genotype will produce recessive phenotype.

3. X-Linked Inheritance: Color Blind Humans Parents: YXb x XB Xb XB = normal Xb = color blind blue = autosome red/green on X Y = determines male Eggs XB(.5)Xb(.5) Sperm • Gametes: • Male = Xb and Y • Female = XB and Xb • Offspring: • 1 normal male • 1 color blind male • 1 color blind female • 1 normal female Y (.5) YXb(.25) YXB(.25) Color Blind Male Normal Male XBXb(.25) XbXb(.25) Xb(.5) Normal Female Color Blind Female

4. Sex-Linked Practice Problems • A woman has a mother and father that have normal vision. Her husband also has normal vision. What are the possible offspring? • Could a father and son both be color blind? • If a mother was color blind and the father normal, would their sons or daughters be color blind? • A normal woman, whose father had hemophilia, married a normal man. What is the probability of hemophilia in their children?

5. Sex-Linked Practice Problem: Fill in the Alleles for Each Individual, use a ? for unknown alleles Affected Male ____ ____ Normal Male ____ ____ ____ ____ Normal Female ____ ____ or ____ ____ ____ ____ Affected Female ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____

6. Human X-Linked Disorders Color Blindness (8% male & 1% female) • Autosomal: blue-sensitive allele • X chromosome: red- and green-sensitive allelles Muscular Dystrophy (1/3,600) • Absence of protein dystrophin • Calcium leaks into muscle cells  death. Hemophilia (1/10,000) • Hemophilia A (clotting factor IX) • Hemophilia B (clotting factor VIII) Fragile X Syndrome (1/1,500 M & 1/2,500 female) • Base triplet repeats (CGG repeated, <50 vs >230) • Hyperactive and autistic, short, large features

7. Gene Linkage Linkage Group: Adjacent alleles on same chromosome inherited together. Linkage Map or Chromosome Map: • Gene order. • Distance between genes.

8. Crossing-Over Occurs between two linked alleles producing offspring with 4 types of gametes (GR, gR, Gr, gr) instead of 2 (GR and gr). Homologous Chromosomes Recombinant chromosomes produce recombinant gametes.

9. Complete Linkage of Loci With No Crossing-Over Complete linkage (no crossing–over produces only parental gametes (gr and GR). Both alleles on the same chromosome always travel together.

10. Incomplete Linkage of Loci With Crossing-Over Crossing-Over produces both parental (GR and gr) recombinant (gR and Gr) phenotypes.

11. Solving Linkage Problems % recombinant phenotypes = % crossing-over • Maps loci position and distance on each chromosome. • 1% crossing-over = 1 map unit.

12. Practice Linkage Problems • If the distance between Gene A and Bis 20 map units and the distance between C and D is 10 map units, what is the correct gene order when A is 5 map units from D? • If A and Bare on the same maternal chromosome and a and b are on the homologous paternal chromosome, what are the gametes with no crossing over? • What are the gametes in # 2 if there was crossing over between the A and B locus? • If you have 100 offspring and 10 of them are non-parental genotypes, what is the percent crossing over? • Normal body and normal wings on fruit flies are linked on the same chromosome. Normal body and wings are dominant. If you cross a homozygous normal body normal wing fly with a black body and curved wing fly, the offspring were 367 normal body and normal wing, 131 normal body curved wing, 139 black body and normal wing, and 363 black body and curved wing. • What is the cross-over frequency between the two genes? • How many map units separate these two genes?

13. Changes in Chromosome Number Also Increase Variation Among Offspring Genetic Variation =crossing-over + independent assortment + fertilization + chromosome/gene mutations. Chromosome Mutations: changes in number and/or structure. A. Number Changes: • Polyploidy: • Number of chromosome sets. 2n = diploid, 3n = triploid, 4n = tetraploid • Major evolutionary force in plants. • 47% of flowering plants • Non-disjunction: Failure of homologous chromosomes to separate Meiosis I Failure of sister chromatids to separate Meiosis II B. Chromosome structure or gene sequence changes

14. Chromosome Number Changes Are Derived From Non-Disjunction Autosomes Monosomy (2n - 1): One chromosome of a homologous pair. Trisomy (2n + 1): Three chromosomes of a homologous pair.

15. Chromosome Number Change: Down Syndrome Trisomy 21: three copies of chromosome 21 77% egg 23% sperm Odds increase over age 40. Extra copy of Gart gene high level of purines in the blood.

16. Polyploid Practice Problems • If a plant has 15 chromosomes, how many chromosomes are in: • The plant stem, flower, root = _____ • The plant sperm cells = _____ • The plant egg cell = _____ • The plant endosperm = _____ • Haploid plant = _____ • Diploid plant = _____ • Triploid plant = _____ • Tetraploid plant = _____ • Monosomy plant = _____ • Trisomy plant = _____

17. Gene Sequence Practice Problems • If chromosome 18 in humans has the genes Cf-vg-G-W-bl-wx-sh-Y-amy in order from the chromosome tip to the centromere, rearrange the genes to illustrate the following: • Duplication • Deficiency • Deletion • What is the difference between a cross-over and a translocation?

18. Chromosomes Chromosome Number Changes in Sex Klinefelter Syndrome (XXY or XXXY, 1/800) • Slow learner, large hands and feet. Poly-X Females (XXX or XXXX, 1/1,500) • Thin and retarded. Jacobs Syndrome(XXY, 1/1,000) • Nondisjunction during spermatogenesis. • Taller than average, speech & reading prob.

19. DNA Genetic information. Parent  Offspring 4 nucleotides Nucleotide sequence = genes Human sequence 99.9% same 46 chromosomes 2 m long .000001 mm wide Tightly coiled - fit in nucleus Wrapped round protein - histones

20. Discovery of DNA 1869: Nuclein found pus cells - high nucleic acid 20th century: • 4 nucleotides found • Protein thought to be genetic material 1952: DNA proven as genetic material 1962: Watson & Crick Double Helix – Nobel Prize

21. Structure of DNA • 4 nucleotides: • Two purine bases • (double ring) • Adenine (A) • Guanine (G) • Two pyrimidine bases • (single ring) • Thymine (T) • Cytosine (C)

22. Chargaff’s Rules • Percent A, T, G, C varies by species • Complementary Base Pairing: Constancy within species Human chromosome = 140 million base pairs

23. DNA Practice Problems • If A is 31.5% in human DNA, what percent is G, C, T, and U? • What is the difference between DNA, chromatin and chromosomes? • If DNA strand 1 is GGTACTAAGCTT, what are the nucleotide sequences for: • DNA strand 2 = • DNA strand copied from strand 1 = • DNA strand copied from strand 2 =

24. Watson and Crick’s 1962 DNA Model • Double Helix Model • Covalent bonded sugar-phosphate backbone = sides • of ladder • Hydrogen bonded • bases = rungs of • ladder • N-H • O-H • Sides of ladder are • anti-parallel • 3’-5’ • 5’-3’

25. DNA Replication • Each old strand - template for new strand • Semi-Conservative Replication • Key Enzymes: • Helicase:unwinds DNA– breaks H bonds • RNA Polymerase:starts point • 3.DNA polymerase:new chain 5’  3’ • 4.DNA Ligase:joins fragments

26. Prokaryotic vs Eukaryotic Replication • Prokaryotic Loop Chromosome: • Replication moves around the • DNA molecule. • Eukaryotic: • Replication begins at numerous • spots (replication fork). • Replication bubbles spread both ways until they meet.