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What are the nitrogenous bases? Which are pyramidine and which are purine?
- pyramidine: A, T
- purine: C, G
(nitrogenous --> DNA)
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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.
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What holds complementary base pairs together?
Weak H bonds
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What 3 things make up a nucleotide?
- 1 deoxyribose molecule
- 1 phosphate group
- 1 base
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How does mutation happen? (2)
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Is spontaneous mutation common? How often does it occur?
Not common: rate is 10^-4 to 10^-7 / gene / generation
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Where does protein synthesis occur?
cytoplasm
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What's a gamete?
How is it formed?
How many chromos?
Hap/diploid?
- sperm/egg cell
- meiosis of diploid cells
- 23
- haploid
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What's a somatic cell? What else are they called?
How is it formed?
How many chromos?
Hap/diploid?
- non-sex cell, aka autosomes (homologous)
- mitosis
- 23 pairs = 46
- diploid
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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.
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What is a chromosome band?
A pattern of stripes that appears on a stained chromo, so that chromos can be ID'd.
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Define euploid.
Having the correct # of chromos.
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Define polyploidy.
Cell has more than the diploid # of chromosomes
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Define aneuploidy.
A cell that does NOT have a multiple of 23 chromos.
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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
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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.
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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.
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What is the incidence of sex chromo aneuploidy for males and for females?
- Male: 1 in 500.
- Female: 1 in 900.
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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
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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
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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
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What are the types of chromo abnormalities?
- Breakages
- Deletions
- Inversions
- Translocations
- Fragile sites
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which has more genetic material, X chromo or Y?
X.
- Y has only ~40 genes.
- A zygote w/o X chromo will not survive.
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fragile X syndrome
- causes retardation
- second to Down syndrome as cause of retardation
- primarily seen in males
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define locus
the place of each gene on the chromo
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define allele
the form a gene takes - its nucleotide sequence
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define genotype
composition of a gene at a given locus
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pedigree symbols:
circle
square
triangle
line thru person
double line connecting parents
target
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
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when enviro factors must be present for a trait to be expressed
multifactorial inheritance
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define proband
first person in a family diagnosed with a disease
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threshold of liability
threshold of genetic and enviro factors that must be present before they are expressed
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polygenic trait
several genes must work together for trait to be expressed
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autosomal dominant
both sexes affected?
generations skipped?
- both sexes affected equally
- no generations skipped
- rare
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define recurrence risk
prob that subsequent children will have the disease.
(# children makes no diff)
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define penetrance, incomplete penetrance
% of individuals w/ a specific genotype that express the phenotype
incomplete: individuals with gene does not exhibit phenotype at all
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define expressivity
extent of variation in phenotype associated with given genotype
(w/ variable expressivity, can have complete penetrance of disease but severity varies greatly)
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define epigenetics
example?
chem modifications that alter expression of genes
ex: DNA methylation. accts for diff b/w ID twins as they age
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what kind of disorder?
males and females affected =
disease seen in siblings, but not usually in parents
consanguinity
lots of carriers
autosomal recessive
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autosomal recessive examples?
- PKU
- CF
- sickle cell
- Tay-Sachs
- Hemochromatosis
- galactosemia
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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
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when is sex determined for fetus?
wk 6 of pregnancy
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define SRY
sex-determining region on the Y, gene on Y chromo that starts male gonad development
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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)
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define sex limited trait, sex influence trait
sex limited: seen in only one sex
sex influenced: more common in one sex
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