Genetics Flashcards
Transcription
mRNA synthesis
in nucleus
How is mRNA different from DNA?
single stranded
ribose backbone, not deoxyribose
Us instead of Ts
Translation
protein synthesis
in ribosome
codon
on mRNA
3 base pairs: code for amino acid
ribosomes
protein factory
make protein out of codon from mRNA and anticodon on tRNA
either in cytoplasm or rER
How many nucleotides? amino acids? codons?
4 possible nucleotides, each w/ 3 base pairs: 4^3=64 possible codons to code for 20 amino acids
allows for redundancy in translate table
single nucleotide polymorphism (SNP)
base pair subsitution
at most only 1 amino acid is changed
very common
allow for no 2 people to look the same
Frame shift mutation w/ one base pair inserted or deleted
the rest of the strand will be messed up
protein won’t work
results will be devastating, t/f uncommon
Single gene disorders
Dominant
Recessive
X-linked: recessive or dominant
Dominant single gene disorder
2 copies of each gene (1 from each parent)
If one bad gene, half of the protein will be bad
If the half bad protein causes a problem, its a dominant disorder
Recessive single gene disorder
need 100% problem to cause disease
both genes must be defective
If only 1 gene is bad, it will be overcome by the good proteins
X-linked single gene disorder
Recessive: all of the Xs need to be defective (from both parents)
More of a problem for males
Translocations
genetic material from 1 chromosome mistakenly put on another chromosome
Deletions
genetic material deleted from a chromosome
Nondisjunction
abnormal # of chromosomes (aneuploidy)
leads to trisomy or monosomy
incorrect separation of chromosome in Meiosis I or Meiosis II
can occur on any chromosome, but only 21, 18, 13 or X are survivable
usually Trisomy
normal: 44 chromosomes + XX or XY
Down syndrome
Down: trisomy 21
maternal age increases chance of trisomy
intellectual disability, facial abnormalities, cardiac problems
Turner syndrome
(45:X) 44 chromosomes + X only monosomy that survives to term and is consistent with life infertile females cardio problems
Klinefelter syndrome
47:XXY
infertile males (some are fertile)
slight decrease in IQ
polyploidy
chromosome sets that don’t = 2
partial mole: triploid: 2X from dad & 1X from mom
usually 69:XXX or 69:XXY
ocassionally go to term but don’t live long
locus
location in the genome
allele
one member of a pair of genes (1 allele from mom, 1 from dad)
Genotype
genetic material
Phenotype
physical manifestation
Penetrance
the chance that phenotype follows genotype
Haplotype
alleles on a single chromosome
Recombination/crossover
gene rearrangement btw homologous chromosomes
occurs during prophase I of meiosis
allows for new arrangement of maternal and paternal alleles on same somatic chromosome
Structure of chromosomes
2 chromatids attached at the middle by centromere
2 short arms and 2 long arms
P: petite arm
Q: long arm
SNP
single nucleotide polymorphism
somatic cell
body cells; not sex cells
reproduced by mitosis
46 (2 pairs of 23) chromosomes in each cell: 22 autosomal and 1 pair sex chromosomes
diploid cell
gamete
sex cells: egg or sperm
only 1 copy of each chromosome
haploid cell
karyotype
chart that places homologous chromosomes in size order matching shape and banding patterns
euploid cells
balanced set of chromosomes (in relation to haploid #
aneuploid cell
abnormal # of chromosomes (in relation to haploid #)
meiosis
how a diploid cell divides for sexual reproduction into 4 haploids
2 fissions occur of the nucleus
4 gametes created: each have 1/2 the # chromosomes as original cell
mixing of chromosomes occur
What happens if nondisjunction occurs during meiosis I?
all gametes are affected
2 have 1 extra chromosome
2 have 1 less chromosomes
What happens if nondisjunction occurs during meiosis II?
half of the gametes are affected
2 normal
1 has 1 extra chromosome
1 has 1 less chromosome
At the end of meiosis, how many of the 4 haploids become sex cells in males?
Females?
males: keep all 4: 4 sperm cells
females: 1 ova, and 3 polar bodies
When does meiosis occur in females?
Males?
Females: all in fetal ovary
males: after puberty
What does crossover allow for?
genetic diversity
What are some errors of crossover?
uneven crossover: 2 copies of a gene
deletion of a gene: cri du chat
* we tolerate additional DNA better then missing DNA
What is chromosome translocation?
cross over btw non-homologous chromosomes (i.e. chromosome 1 from mom and chromosome 2 from dad mix together)
If a child has balanced translocation how will this affect them?
They will have the right amount of DNA but when they go to have kids, the chances of combining DNA in the correct amounts is very low: alot of spontaneous abortions
Also…problems at the edges w/ mutated proteins: increased risk of Ca
What are some examples of Dominant single gene disorders?
Familial hypercholesterolemia Huntington Achondroplasia Marfan Retinoblastoma Li-Fraumeni
What are some examples of Recessive single gene disorders?
sickle cell anemia cystic fibrosis lysosomal storage diseases (Tay-Sachs, Gaucher, Nieman-Pick) Phenylketouria Glycogen storage disease
What are some examples of X-linked recessive single gene disorders?
Duchenne muscular dystrophy Hemophilia A (factor VIII) or B (IX)
In a pedigree, what does each symbol mean? empty circle empty square empty diamond darkened square or circle square or circle w/ line through it
empty circle: unaffected female
empty square: unaffected male
empty diamond: unknown sex
darkened square or circle: affected male or female
square or circle w/ line through it: dead
If 2 people have a dominant disease (Dd), how likely is it that they will have a:
homozygous affected
heterozygous affected
homozygous normal
homozygous affected: 25% (rare)
heterozygous affected: 50%
homozygous normal: 25%
If 1 person has a dominant single gene disorder (Dd) mates with a normal person (dd), how likely is it that they will have a:
homozygous affected
heterozygous affected
homozygous normal
homozygous affected: 0
heterozygous affected: 50%
homozygous normal: 50%
If 2 people are carriers of a recessive single gene disorder, what is the likelyhood they will have a
homozygous affected
heterozygous carrier
homozygous normal
homozygous affected: 25%
heterozygous carrier: 50%
homozygous normal: 25%
How does X inactivation work?
occurs in embroyo of female: inactivation occurs and cells will either have an active paternal X or maternal X
“X chromosome mosaics”
If a normal male mates w/ a female carrier of an X-linked recessive gene, what is the likelyhood that there will be a
normal daughter/ son
carrier daughter/son
affected daughter/son
normal daughter: 25%; son: 25%
carrier daughter: 25%; males: 0
affected son: 25%; females: 0
If a normal female mates w a male affected by an X-linked recessive disease, what is the likely hood they will have a
normal daughter/ son
carrier daughter/son
affected daughter/son
normal daughter: 0 son: 50%
carrier daughter: 50% son: 0
affected daughter/son: 0
if a carrier female mates w/ a male w/ a recessive gene disease, what is the likely hood they will have:
normal daughter/ son
carrier daughter/son
affected daughter/son
normal daughter: 0 son: 25%
carrier daughter: 25% son: 0
affected daughter: 25% : 25%
What are epigenetic modifcations?
we can actually turn off some genes
- generation skipping phenomena
- genes that are methylated can’t be expressed but can be passed to your offspring
