Chapter 3

1. Chapter 3 Human Genetics

2. RNA – Ribonucleic Acid Differs from DNA in that: • Contains the sugar Ribose • Is mostly single stranded • Contains the base Uracil instead of Thymine

3. Transcription • The synthesis of RNA on a DNA template (copying process that makes RNA)

4. Process of Transcription: 1: RNA polymerase binds with part of the DNA strand 2: RNA polymerase unwinds a portion of the double helix (separating the strands). RNA nucleotides pair with complementary bases one at a time 3: A continuous RNA strand is formed 4: The RNA molecules separate, polymerase comes off, and the DNA strands rejoin

5. The product of transcription is RNA • Messenger RNA (mRNA) • Transfer RNA (tRNA) • Ribosomal RNA (rRNA)

6. Information flows from DNA  RNA  Protein Translation (protein synthesis)

7. DNA canNOT leave the nucleus What does mRNA do? Carries DNA information to the ribosomes Is used to make protein Why is mRNA made?

8. How does mRNA make proteins? • At the ribosome, mRNA assembles amino acids into chains • Codons – group of 3 nitrogenous bases • tRNA helps assemble the AA • AA chains combine to form proteins

9. tRNA • Carries anticodon and an amino acid

11. Figure 3.4

12. Figure 3.5 (1)

13. Figure 3.5 (2)

14. Figure 3.5 (3)

15. Translation uses all 3 forms of RNA: • mRNA as the template • tRNA to match a codon to an amino acid • rRNA to form the platform where the process takes place

16. Figure 3.2a

17. Mutations • Heritable changes in DNA sequence • Can result from mistakes during DNA replication • Are fixed by mechanisms in your body • In somatic cells can affect individuals but not necessarily the next generation • In gametes may be passed on to the next generation

18. Point Mutations • Single-base mutation Eg. Substitution of 1 nitrogenous base for another

20. Frameshift Mutation • 1 or 2 extra nitrogenous bases are inserted/deleted into a DNA sequence

22. Chromosomal aberrations (larger changes in genes) Chromosomal fragment may: • Be duplicated • Become attached at new location • Be lost completely • Be inverted and reinserted (*most frequent) • Change in chromosome #

23. Karyotype – an arrangement of homologous chromosome pairs • Autosomal chromosomes – same in both sexes (22 of 23 pairs) • Sex chromosomes – 23rd pair; have a role in determining the sex of an individual (most of the genes on the X chromo. are not on the Y chromo.)

24. Genes that are carried on sex chromosomes determine sex and sex-linked traits

25. Females XX Males XY Sex determination

26. male female

27. Exceptions to the rule: Not all females are XX and not all males are XY A cross-over during meiosis can occur between an X & Y chromosome and is followed by an exchange of DNA pieces ---translocation • 1/20,000 normal males is XX (chromosomally) 1 of X chromo. contains small translocated piece of Y chromo. • 1/20,000 normal females is XY (chromosomally) missing same small piece of the Y chromo.

28. Lead to the assumption that: • An XY female has 99.8% of the Y chromosomal DNA; therefore, the male-determining factor must be located in the .2% portion of the chromo. she did not have • The .2% of the chromo. has the sry gene – which is thought to induce male development www.biointeractive.org

30. Sex-linked traits • Most genes are located on the X chromo. • Genes that are on the X chromo. and not on the Y chromo. are sex-linked genes

31. Females Can be either homozygous or heterozygous for sex-linked traits (b/c they have 2 X chromo. and 2 alleles of every sex-linked gene) Males Because males only have 1 X chromo., they have 1 allele for each sex-linked trait (which determines his phenotype for the trait) Hemizygous e.g., red-green colorblindness

32. Trait: red-green colorblindness Genotype: (XCY x XcXc) Phenotype: male is normal, female is colorblind Male gametes XC Y Female gametes Xc Xc

33. Trait: red-green colorblindness Genotype: (XCY x XCXc) Phenotype: male is normal, female is carrier (normal) Male gametes XC Y Female gametes XC Xc

34. Chromosomal variation • Normal human – 22 pairs of autosomal chromo. 1 pair of sex chromo. • Any difference in chromosomal # has consequences  called syndromes

35. Klinefelter’s syndrome XXY Male phenotype Sterile Some symptoms treated with hormones Turner’s syndrome XO Female phenotype Infertile (ovaries do not produce female hormones, therefore puberty isn’t reached and gametes do not develop) Some symptoms treated with hormones Variations in sex chromosomes:

36. Klinefelter’s

37. Figure 2.15

38. Klinefelter’s and Turner’s are thought to result from nondisjunction • Nondisjunction – abnormal cell division of sex chromo.

41. Variations in autosomal chromosomes: Down’s syndrome • Trisomy 21 • Distinct facial characteristics • Heart abnormalities • Variable amounts of mental retardation

42. Frequency of Down’s Syndrome

44. Patau’s syndrome or Trisomy 13 Small head, extra fingers and toes Cleft lip, large triangular nose, wide-spaced eyes Severe mental retardation Death usually by 1 year Variations in autosomal chromosomes:

45. Trisomy 13 karyotype

46. Variations in autosomal chromosomes: Cri du chat syndrome (Cry of the Cat) • Deletion in chromosome 5 • Small head, mental retardation, catlike cry • Short lifespan • 1 in 50,000 births

47. Cri du chat karyotype

48. Other diseases and abnormalities that are inherited in genes: (not chromosomal aberrations) • Albinism • Single mutation that prevents the formation of the pigment melanin (which blocks ultraviolet light) in eyes, skin, hair and internal organs • Affects all races of humans and other species • In U.S. 1 in 17,000 people have some type of albinism

49. Pedigrees • Diagrams giving the pattern of mating and descent of certain traits • most basic methods for presenting genetic data • are most useful when they span many generations

50. Pedigrees help determine if traits are: • Inherited • Dominant or recessive • Have a more complex genetic basis