week 5 (chromo. abnormalities) Flashcards
question: what are the arms of a chromosome called?
- shorter arm = p
- longer arm = q
define: metacentric, submetacentric, acrocentric, and telocentric
- meta = p and q roughly same
- submeta = p shorter than q
- acro = chromosomal fragments (satellite) + short is extra short
- telo = no p arm
explain: fluorescent in situ hybridization
- using probes to detect target seq.
- can be used to ID each chromo. in a cell
explain: chromo. banding techniques
- older method than FISH
- ID chromo. based on size, shape, and banding patterns when dyes and stains used
- stops cell cycle in metaphase
define: euchromatin vs heterochromatin
- euchromatin = lighter regions
⤷ chromatin less compact = regions w/ higher gene expression - heterochromatin = darker regions
⤷ chromatin more compact = regions w/ lower gene expression
define: nondisjunction
- failure of chromo. and sister chromatids to properly separate during division
- in either meiosis I or II
explain: possible results of nondisjunction in X chromo. of a female
1. nondisjunction in meiosis I
⤷ 1 cell gets both copies of chromo., other gets none
⤷ 2 daughters have 2 Xs, 2 daughts have no Xs
2. nondisjunction in meiosis II
⤷ each cell gets on copy of chromo.
⤷ daughters can either get 2 Xs, 1 X, or no Xs
explain: meiosis I nondisjunction
- homologues fail to separate into 2 cells
⤷ one gets all, other gets none - when fertilized, gametes with 2 X -> trisomic, gametes with 0 X -> monosomic
explain: meiosis II nondisjunction
- homologs separate like normal
- sister chromatids fail to separate
- can also have trisomic and monosomic after fertilization
define: aneuploidy
- abnormal number of chromo.
- humans and most animals very sensitive
⤷ most don’t survive gestation - plants not as sensitive
explain: trisomy 21
- down syndrome
- most well known and studied aneuploidy in humans
- link between maternal age and risk of down syndrome
⤷ increase age = increase risk
explain: robertsonian translocation
- two non-homologous chromo. fuse to form one big chromo.
- forms basis to down syndrome inheritance
- case: fuse 14 and 21
⤷ if gamete with fused chromosome and chromo. 21 is fertilized -> trisomy 21
define: polyploidy
- presence of 3 or more sets oof chromo.
- common in plants
question: autopolyploidy vs allopolyploidy
- auto = can occur from duplication of chromo. w/in a sp.
- allo = can occur from combining sets from diff. sp.
name: causes of auto and allopolyploidy (3)
1. meiotic nondisjunction
- leads to diploid instead of haploid’
2. mitotic nondisjunction
- doubles chromo. number early in fertilization
-> all cells have doubled chromo.
- combo of both
name + define: types of chromosomal deletions
1. terminal deletion
- entire chromo. arm or part of it severs
- ex. cri-du-chat
2. acentric
- lacks centromere
- often gets lost in division bc no centromere to kinetochore
3. interstitial
- internal chromo. deletions
question: what can result from a chromo. breakage?
- chromo. reattaches
⤷ if not critical genes mutated, can be pheno. normal - chromo. inversion
⤷ reattaches at wrong end
⤷ reattachment to non-homologous chromo. -? chromosome translocation
name + define: types of chromosome inversions (2)
1. paracentric
- centromere outside inversion
pericentric
- centromere w/in inversion
question: what happens to recombination w/ chromosome inversions?
- inversions usually suppress recomb. in het.
- but can still happen
⤷ can cause chromo. breakage
⤷ large deletions -> inviable offspring
⤷ forms inversion loop
define: unequal corssover
- one way crossover
- partial duplication on one, and partial deletion on the other
- rare
- ex. williams-beuren (chromo. 7)
⤷ naive, outgoing, mild intellectual disabilities and heart problems
define: deletion mapping
- mapping genes based on comparing pheno. of interest w/ known deletions
⤷ usually when already know general area - mut. must be rec.
⤷ bc if recessive on one allele, and deletion on other -> mutation is expressed
