208 Genetics

  1. What are the nitrogenous bases? Which are pyramidine and which are purine?
    • pyramidine: A, T
    • purine: C, G

    (nitrogenous --> DNA)
  2. The double helix of DNA is formed by a ladder made of what? What kinds of bonds are present in the ladder between these?
    Ladder made of sugar and phosphate. Connected by phospodiester bonds.
  3. What holds complementary base pairs together?
    Weak H bonds
  4. What 3 things make up a nucleotide?
    • 1 deoxyribose molecule
    • 1 phosphate group
    • 1 base
  5. How does mutation happen? (2)
    • -mutagens
    • -spontaneous
  6. Is spontaneous mutation common? How often does it occur?
    Not common: rate is 10^-4 to 10^-7 / gene / generation
  7. Where does protein synthesis occur?
  8. What's a gamete?
    How is it formed?
    How many chromos?
    • sperm/egg cell
    • meiosis of diploid cells
    • 23
    • haploid
  9. What's a somatic cell? What else are they called?
    How is it formed?
    How many chromos?
    • non-sex cell, aka autosomes (homologous)
    • mitosis
    • 23 pairs = 46
    • diploid
  10. What is a karyotype?
    • Lecture: Orderly display of chromos.
    • N. Central: a photomicrograph of the chromos of a single cell, taken during metaphase, when each chromo is still a pair of chromatids. Then the chromos are arranged in numerical order, in descending order of size, with the sex cells last.
  11. What is a chromosome band?
    A pattern of stripes that appears on a stained chromo, so that chromos can be ID'd.
  12. Define euploid.
    Having the correct # of chromos.
  13. Define polyploidy.
    Cell has more than the diploid # of chromosomes
  14. Define aneuploidy.
    A cell that does NOT have a multiple of 23 chromos.
  15. Define trisomy. Give an example.

    Which are the most common trisomies?
    • Lecture: Having 3 copies of 1 chromo.
    • N. Central: Having 3 homologous chromos per cell instead of 2.

    • Trisomy 21 = Down Syndrome
    • Trisomy 13, 18, 21
  16. Define monosomy. Give an example.
    Having only one of a pair of chromos.

    Ex: Turner's syndrome = only one X chromo instead of the normal pair.
  17. Is Down syndrome related to maternal age? How?
    Is Down syndrome related to paternal age? How?
    • Maternal: risk ^^^ with age.
    • Not related to paternal age.
  18. What is the incidence of sex chromo aneuploidy for males and for females?
    • Male: 1 in 500.
    • Female: 1 in 900.
  19. What is the chromosomal basis for Turner syndrome? What are signs of the disease?
    Aneuploidy of the 23 chromo pair, having only one X (and no Y). 45, X/0

    • –short height
    • –female genitalia
    • –webbed neck
    • –underdeveloped breasts, imperfect ovaries
    • –widely spaced nipples
    • –shield-like chest
  20. What is the chromosomal basis for Klinefelter's syndrome? What are signs of the disease?
    XXY = Klinefelter syndrome 47, XXY or 48, XXXY

    • –small testes
    • –gynecomastia (enlargement of breast tissue in males. moobs)
    • –sparse body hair
    • –long limbs
  21. Define clastogen.
    What are some examples? (4)
    Any agent that can damage a chromo.

    • radiation - x-rays
    • certain chemicals
    • extreme changes in the cellular enviro
    • viral infections
  22. What are the types of chromo abnormalities?
    • Breakages
    • Deletions
    • Inversions
    • Translocations
    • Fragile sites
  23. which has more genetic material, X chromo or Y?

    • Y has only ~40 genes.
    • A zygote w/o X chromo will not survive.
  24. fragile X syndrome
    • causes retardation
    • second to Down syndrome as cause of retardation
    • primarily seen in males
  25. define locus
    the place of each gene on the chromo
  26. define allele
    the form a gene takes - its nucleotide sequence
  27. define genotype
    composition of a gene at a given locus
  28. pedigree symbols:
    line thru person
    double line connecting parents
    half-shaded shape
    shaded shape
    • circle - female
    • square - male
    • triangle - sex unknown
    • line thru person - dead
    • double line connecting parents - consanguinous mating
    • target - X-linked carrier
    • half-shaded shape - carrier
    • shaded shape - affected individual
  29. when enviro factors must be present for a trait to be expressed
    multifactorial inheritance
  30. define proband
    first person in a family diagnosed with a disease
  31. threshold of liability
    threshold of genetic and enviro factors that must be present before they are expressed
  32. polygenic trait
    several genes must work together for trait to be expressed
  33. autosomal dominant

    both sexes affected?
    generations skipped?
    • both sexes affected equally
    • no generations skipped
    • rare
  34. define recurrence risk
    prob that subsequent children will have the disease.

    (# children makes no diff)
  35. define penetrance, incomplete penetrance
    % of individuals w/ a specific genotype that express the phenotype

    incomplete: individuals with gene does not exhibit phenotype at all
  36. define expressivity
    extent of variation in phenotype associated with given genotype

    (w/ variable expressivity, can have complete penetrance of disease but severity varies greatly)
  37. define epigenetics
    chem modifications that alter expression of genes

    ex: DNA methylation. accts for diff b/w ID twins as they age
  38. what kind of disorder?
    males and females affected =
    disease seen in siblings, but not usually in parents
    lots of carriers
    autosomal recessive
  39. autosomal recessive examples?
    • PKU
    • CF
    • sickle cell
    • Tay-Sachs
    • Hemochromatosis
    • galactosemia
  40. define Barr bodies
    how many do normal females have? males?
    when is Barr body inactivated?
    inactivated X's become condensed intranuclear chromatin, seen in interphase

    • females normally have 1, males have 2. (# Barr bodies = # X chromos - 1)
    • inactivated 1-2 wks after fertilization
  41. when is sex determined for fetus?
    wk 6 of pregnancy
  42. define SRY
    sex-determining region on the Y, gene on Y chromo that starts male gonad development
  43. what kind of disorder?
    seen more in males than females
    never transmitted from father to son
    skips generations
    X linked

    (if father has gene, all his daughters will be carriers)
  44. define sex limited trait, sex influence trait
    sex limited: seen in only one sex

    sex influenced: more common in one sex
Card Set
208 Genetics