Genetics Flashcards
How many chromosomes do you have?
46
22- 2 somatic copies
Male XY
Female XX
What is transcription?
DNA–> mRNA
What is translation?
mRNA–> protein
What is RNA polymerase
Makes RNA copy
What is DNA polymerase?
Makes DNA copies
Difference between RNA and DNA
- RNA single strand- DNA double
- T on DNA is U on RNA
- Deoxyribose nucleic backbone on DNA and ribose backbone on RNA
General process for protein synthesis?
- DNA–> mRNA (transcription)
- mRNA–> cytoplasm and ribosome
- Ribosome uses mRNA to make protein
- add amino acid to polypeptide chain, one codon at a time (3 nucleotides at a time)
- can happen in cytoplasm on free ribosome or on ribosome on rough ER
What is a SNP
?
Single nucleotide polymorphisms
single nucleotide changed
What is a frameshift mutation?
One base pair deleted or inserted causes all remaining amino acids to be coded wrong
Major implication on protein formation
What are is an X-linked gene disorder?
- Disorder on x chromosome
- FOr man- every x chormosome affected
- for women- only one x chromosome affected
- For dominant diseases- only one needs to be affected
- in male, most likely die in utero. very rare
- For recessive diseases- affect men but not really women
What is aneuploidy? Examples?
multiple copies of chromosomes or only one
Examples
- Down syndrome (trisomy 21)
- Turner (45:X)
- Klinefelter (47: XXY)
Getting extra copy of chromosome is less of problem than getting one less
What is polyploidy?
Having a WHOLE extra set of chormosomes (will have 68 instead of 46)
Real life example- seedless watermelon
What is a locus?
location in the genomes
What is an allele
one member of a pair of genese
What is genotype?
genetic material
What is phenotype
physical manifestations of gene
What is penetrance
chance that phenotype follows genotype
What is haplotype
alleles on single chromosome
What is recombination/corssover?
Gene rearrangement between homologous chromosomes
What is the short arm of the chromatid abbreviated as? Long arm?
short arm= p
long arm = q
Stages of meiosis? Where does it happen?
happens in germ cells
For females
- In utero (week 9) make oogonia
- oogonia–> oocytes
- oocytes start meiosis I- stop around anaphase I
- When born, no more eggs made
- when oocyte awakened in puberty–> continue to meiosis II
- Only when egg meets sperm, will oocyte finish mesosis II
- other 3 become polar bodies and are thrown away
- process makes 4 total copies, but only 1 used
What is a nondisjucntion?
When chormosomes don’t pull apart after crossover
how we end up with trisomy/monosomy in offspring
What increases risk for disorders of nondisjunction?
increased maternal age
What is turner syndrome?
- Sex chromosome missing (45:X)
- Typically infertile
- characteristics- short stature, female genitalia, webbed neck, shieldlike chest with underdeveloped breasts and widely spaced nipples
- Tend to have cardiac problems and die around 50
What is klinefelter syndrome?
- Extra X chromosome (47, XXY)
- small testest
- some development of breasts
- sparse body hair
- long limbs
What is crossover?
- shuffling and mom and dad’s chromosome 1 prior to splitting during meiosis
What are some issues that can occur with chormosome crossover?
- Deletion occurs when chormosome segment is lost
- generation of duplication and deletion through unequal crossing over
- ex- cri du chat- deletion of part of 5q
What is translocation?
Crossover between non-homologous chromsoomes (ie dad chormosome 2 and mom chromosome 3 got together for crossover)
- Initial off spring (those created with that crossover) will be ok as long as balanced translocation
- However, that offspring will have trouble producing offspring
- also more susceptible to Ca
What are some dominant single gene disorders?
- Familial hypercholesterolemia
- retinoblastoma
- li-fraumeni
- porphyria
- huntington dx
- achondroplasia
- marfan
Only need one gene affected in order to be affected
Example recessive single gene disorder?
- Sickle cell anemia
- Cystic fibrosis
- lysosomal storage dx (Tay Sachs- Gaucher- Miemann-pick)
- Glycogen storage dx (von Gierke, Pompe, McArdle)
- Phenylketonuria
- Hemochromatosis
- Wilson’s disease
Need both genes to be bad to cause a problem
Example x-linked recessive dx?
- Duchenne muscular dystorphy
- hemophilia A (factor VIII) and B (factor IX)
- Lesch-nyhan syndrome
Familal hypercholesterolemia?
- Dominant single gene d/o
- defect in cholesterol receptor–> high cholesterol
- If get one gene from mom/dad–> only 1/2 good receptors on cell, liver gets message to increase cholesterol
- liver begins to make more cholesterol (double)
- If both genes bad–> no good receptors and usually die in utero
- if somehow you survive utero–> typically first MI very young (1yo or so)
What is porphyria?
- defect in porphyrin enzyme–> buildup of intermediat product
- dominant- single gene
- Anemia, people look like they should be dead
Huntington disease?
- Dominant
- increase in repeating CAG count (triple nucleotide repeat, longer the repeat, the more problems) –> neuro-degeneration similar to parkinson’s
Achondroplasia?
- Dominant single gene
- FGFR 3 mutation–> decreases bone growth
Cystic fibrosis?
- Recessive gene
- defect in Cl transporter
- 1 bad transporter- still move chloride, just at half rate
- 2 bad- then get cystic fibrosis
Lysosomal storage dx?
- Defect in lysosomal enzyme–> cells fill with debris
Phenylketonuria?
- Recessive
- Defect in enzyme that converts phenylalanine to tyrosine
- again, 1 bad gene, ok, just convert slower
- 2 bad genes- problems with buildup of intermediate products
Hemochromatosis?
- Dysregulation of iron uptake–> iron overload
- txmt- blood transfusion
Wilson’s disease?
- defective copper transporter for biliary excretion–> copper overload
- Recessive gene
Who is more affected by x-linked recessive diseases?
men
women tend to be carriers
- women have 2 copies X, so if one bad, usually fine, just carriers
- men- only have one copy of X. Takes one defective gene to not work
Dominant x-linked genes typically die in utero
Do you have to inherit trait for achondroplasia?
no, can be spontaneously mutates, but rare.
What is likelihood of offspring having disease when 2 affected parents have a dominant disease?
3/4 children will have disease
1/4 unaffected
What is likelihood of offspring being affected with dominant disease when one parent has a disease and one does not?
1/2 affected
1/2 unaffected
In a recessive disease, how many would be affected if both parents carriers?
1/4 potentially affected (homozygous affected)
2/4 heterozygous carriers
1/4 normal (homozygous normal)
What is the X-inactivation process?
- In zygote and early embryonic cells, maternal and paternal X chromosomes are botha ctive
- X inactivation takes place in uterine development
- all cells individually flip a coin, and turn off one of the x’s
- so, women are mosaics with either mom or dad’s x chormosome working
*
What is example of a system affected by X inactivation process?
- hepatocytes- gene for clotting factors carried on x-chromosome
- if female and inherited faulty x from mom- half of hepatocytes have functioning chromsome, half dont
- make 1/2 clotting factors, can generally be ok
- if male and inherited faulty x from mom- that’s the only x you have and ALL hepatocytes incorrectly make coag factors- screwed
- if female and inherited faulty x from mom- half of hepatocytes have functioning chromsome, half dont
What is a barr body?
- Inactive x chromsome in female
- not fully inactive, but about 99% inactive
What is likelihood of offspring having x-linked dx if mom is carrier and father is normal?
2/4 unaffected
1/4 carrier
1/4 affected
What is likelihoood of offsping having x-linked diseaes if mom is unaffected and not carrier and dad is affected?
1/2 are carriers
1/2 normal
What is likelihood of offsping having x-linked disease if mother is carrier and father affected?
1/2 have the disease
1/4 carrier
1/4 normal
What is duchenne muscular dystophy?
defect in sarcolemma–> muscle damage and wasting
recessive
What is hemophilia A and B?
lack of factor VIII (A) or IX (B)
Recessive
What is lesch-nyhan syndrome?
lack of purine production–> uric acid overproduction
What is epigenetics?
- Summary- how we can have genes skip a generation
- When you make gametes, disable some of the gene (via methylation)
- there’s a male and female pattern for doing this
- female will disable certain genes
- egg with gene turned off (every female does this)
- kid made with egg, kid has 2 copies of every gene but mom’s copy turned off, only dad’s copy active
- Men have diff pattern activation
- turn off diff genes than female
- kid has some of mom’s genes turned off, some dad’s gene turned off
- won’t affect kid BUT when daughter goes to make egg, takes gene from one or other using cross over
- can take gene in dad active in her, put it in egg and turn it off
- can have gene from father but not express characteristic
What happens if environment changes suddenly?
- We want kids that are adaptive to environment
- we can change DNA, turning on and off genes based on our environment
- if famine- make epigenetic modification to turn off hunger gene
- bascially, we can immediately affect our genes to affect future generation
- ex with fetal alcohol syndrome, animal in swamp that make alcohol
