Anuiploidy + non-disjunction Flashcards
Iclicker 1
Diploid – have 2 copies of Homologous Chromosomes
- 2 chromosomes (count by # of centromeres)
iclicker 2
Still diploid – # of dsDNA strands changes BUT still only 2 chromsomes – still diploid
iclicker 3
After anaphase – have 1 copy of HC
- Seperated = haploid
Ploidy in Meiosis
Dplioid –> Diploid –> Haploids (during Anaphase)
- Meiosis 2 = get haploid
- After anaphase each cell has 1 copy of HC
Ploidy
Number of copies
Example – humans are diploid –> 2 copies of all 23 unique chromosomes
slide 14 - What is the ploidy of this human cell?
Triploid – have 3 copies of each chromsome
Polyploid
When there is over 2N (over diploid) for every chromosome
- Every cell has same # of chromosomes and its more than normal for that sepcies
Aneuploid
An abnormal number of one or more chromosomes
- Have non-typical number at one or more than one but not all
Ex. Trisomy 21 –> Downsyndrome
Polyplodit stability
Animals – Polyploidy is lethal in most animals
Fungi – Ploidy is unstable in fungi
Plants – Many plants are tolerant of polyploidy
Polyploidy in plants
Polyploidy tends to lead to larger fruits/flowers
- Common in plants because get bigger fruit
Well tolerated in plants
Triploids are usually sterile because 3 chromsomes don’t know how to line up during metaphase
Example – plants were diploid and had seeds that trun balck and now they are triploud and now seeds don’t trun black
Example 2 – Strawberry
Small = wild = diploid
Big = Octoploid
Triploid plants
Are usually sterile – because three chromosomes don’t know how to line up during metaphase
How does polyploid occur
Ploidy cell typically organinate when spindle fibers don’t form correctley during meiosis
- Arise due to mistake in mitosis or meiosis
- HC alugn on splindle that pulls them apart –> if prevent spindle from forming = won’t be pulled = stay in the middle
- Spindle fibers cam’t form = seperarting chromsomes = stay in teh same cell during cytokenesis
Mutation preventing from spindle from forming
The two seperating chromosomes stay in the same cell during cytokensis
- No spindle = chromosomes stay together
One cell = has no DNA
One cell = has double DNA – one cell has extra copy of every chromosome
Disjunction
The seperation of chromosomes
When does disjunction occur
Mitosis – Anaphase
Meiosis – Anaphase 1 and Anaphase 2
Nondisjuction
When chromosomes or sister chromatids fail to seperate
Chromosomes = not seperating –> ALL dragged to one side of the cell
What leads to Annupliody
Non-disjuction – mistake in disjunction
When can nondisjunction occur?
Mitosis + meiosis 1 + meiosis 2
Can occur in males and females
How many chromosomes does nondisjunction usually affect
Typically only affects 1 chromosome
ALL others segragate normally
Result of nondisjunction
Results in varaition in chromsome number – ganates with the wrong number of chromosomes
Nondisjunction in M1 – 2N, 2N , 0N , 0N
Nondisjunction in M2 – 2N, 0N, 1N, 1N
***Add in image
How often is nondisjunction
Rare event – mistake in meiosis
- More likley in one cell
Even more rare if have nondisjunction in Meiosis 2 that it will occur in both cells in Meiosis 2 – will only occur one cell (because rare)
Slide 22 – iclicker
2N + 1N –> get 3N
Slide 23 – iclicker
Meiosis 1 – Because 2 gamates with 2N than in Meisosis 2 (have 2 2N in meiosis 1 and 1 2N in meiosis 2) = more likley to get 2N – can the combine to get 3N
Result of fertalization after annuploidy
Meiosis 1 – 2N –> 3N
0N –> 1N
2N + 2N + 0N + 0N —> 3N + 3N + 1N + 1N
***3N = trisomy
End = get trisomy
Meiosis 2 – 2N + 0N + 1N + 1N –> 3N + 1N + 2N + 2N
iclicker
XXX, XXX, XO, XO
Affect of most anueplodies in humans
Are lethal
Viable human autosomal Anuploides
- Trisomy 21 – Downs syndrome
- trisomy 13 – Patau Syndrome
- trisomy 18 – edwards syndrome
***trisomies 9 and 8 are very rare
Liklihood of NJ in one chromosome vs. another
There is nothing specieal about NJ in one chromosome or othr –> Chromsome 21 is NOT more likley to have NJ its just that most are not viable so we do not see results of NJ in other chromsomes
Seeing trimosy 21 is NOT because 21 is more likley to have NJ its that the other NJ are not going to be viable = won’t see others
Affect of Annuploidy + Miscarrige
10-20% of preganacey end through miscarige –> 35% of fetuses in a miscarrige have anuiploides
How common is NDJ
NDJ leading to annuplodies is common
10-20% of preganacey end through miscarige –> 35% of fetuses in a miscarrige have anuiploides
Sex chromosome anuploides
Humans are very tolerant to sex chromosome aneuploides
Ex. XXY – Kleinfelter synderome
Ex 2. XO – Turner syndrome (viable but more of phenotype than Kleinfelter synderome)
Kleinfelter synderome
Lots of phenotypic varaition – many XXY males will never know unless a karyotype is preformed
Taller + might have femanized characteristics BUT might have no real phenotype
Very viable
Example Sex chromosome anuploides
XO – truners Syndrome
XXY – Kleinfelter synderome
XXX – Triple X syndrome (phenotypically normal – sometimes developmental delays and sometimes low fertility)
XXXX – Tetrasomy X (phenotypically normal – sometimes developmental delays and sometimes low fertility)
XXXXX – pentasomy (phenotypically normal – sometimes developmental delays and sometimes low fertility)
XYY – Jacobs syndrome
XXY – Jacobs syndrome Misconception
Phenotypes can (but most often do not) include developmental delays + delayed speech + poor muscle tone + taller and thinner than average)
MISCONCEPTION – They are hyperagressive
XYY males are NOT hyperaggressive (the first reprots of XYY karyotypes were from federal prisomners with no “general popultion” controls and small sample sizes)
Why are X inactivation so tolerant to anueplodies
X inactiveation and dosage compensation
Lyonization
X-inactivation
Mary Lyon
Determines that 1 X chrosmomes could be inactived to prevent gene expression from both X chrosmomes
X-inactivation
1 X chrosmomes could be inactived to prevent gene expression from both X chrosmomes
One X chromosome is randomly inactivated during embryonic development through chromatin condensing (lyonizatioon) forming Barr bodies
X chrosmome expression in females
Females (XX) do NOT express twice as many X-linked genes than males (XY) –> One X chromosome is randomly inactivated during embryonic development through chromatin condensing (lyonizatioon) forming Barr bodies
- One of the X chromsomes is selected for X inactivation –> condensed to form Barr Body
X-inactivation process
Done through chromatin condensing (forms Barr body(
X inactivation in marsupials
In some Marsupials the X chromosome in the sperm is inactivated
Example of X inactivation
Seen in female cat – all cells have XB and XO BUT only one is expressed
- One cell - have only active organge
- some cells - have only active Black
Makes some cells organge phneotype and some cells black phenotype = get calico cat –> NOT having one cell that is half orange and half black
get mosaic of cells
***Add in slide 33 image)
Dominance on organismal vs. cellular level
SHOWS that dominace relationships are contexual
XB and XO are codominant (See both orange and black fully) at the organismal level BUT At the cell level there is no relationship because they are both hemizygous (because only 1 of the X chromosomes is actually active)
- Only one is expressed NOT black and organge in one cell
Women as mosaic
Woemn have some cells that expressed one X from mom and some cells that expresses X from dad
Males = just express the X from mom
Result of X inactivation
Have one X chromsome that is active and all other sare condensed to Barr bodies
Counting number of Barr bodies
of bar bodies = # of X xhromsomes - 1)
XXY = 2-1 = 1
XXX = 3-1 = 2
Iclicker page 36
2, 0, 0
XXX = 3-1 = 2
XY = 1 - 1 = 0
XYY = 1 - 1 = 0
Why are there any phenotypes for sex chromosome anuplodies?
Reason why think this = because shouldn’t X-inactivation balance out the extra X chromsomes
Reasons why have phenotypes:
1. Sometimes need expresison for both X then one is silenced
- Sometimes get some gene expression –> Sometimes too much is a bad thing
- Some gene expression occurs from the condensed X chromosome
- Chromosome structure is dynamic
- X-inactivation may not be complete
Example – what Xlinked genes contributeds to the short stature and congintive abnoramalutes of someone with Turner syndrome – Maybe SHOX (Short-stature homebox containing gene) maybe otehrs too
Haploinsufficiencey
When 1 copy of a gene is not enough to produce the wild-type phenotype
Mechanism of X-inactivation
- Initiation – A specific RNA binds to one of the 2Xic genes at random
- Spreading – This intiates a cascade to coat the rest of the chromosome
- The X-chromosome that is coated condesed into a Barr body
What is associated with human anuploidies
Human aneuploides are associated with maternal age – pribability of annuploidy increases in age
Spematogenetsis
Occurs in adults all of the time – smaller than eggs
Division in Oogensis
There is an unequal division of cytoplasmic componenets – The cells that don’t get “the goods” become polar bodies
Keeps all of the proteins and resources to make egg that will be used to give to fetus – cells w/o the goods = polar bodies
Polar bodies
The cells that don’t get “the goods” during Oogensis
Contain DNA but not realy anything else
Result of Oogensis
1 cells + 3 polar bodies
***Add in imaghe on slide 41
Oogensis
Begins in Utero and finsihes at menapause
begins in Utero – THEN the primary oocytes are paused in prophase 1 –> meiosis restarts in puberty
- Have oogensis restart one cell at a time monlthy until menapause
Where are oocytes pasued in?
Prophase 1
Older cells in Oogensis
Older cells have trouble seperating the cohesion proteins in the synaptonemal complex that hold the HC togetehr = REASON HAVE MORE NDJ WHEN HAVE OLDER WOMEN
- Proteins that hold chromsomes togetehr in prophase get older = degrade = more likley to make mistakes and not seperate chromosomes
Oogensis (MINE)
Before puberty – egg cells initiate meisois —> stay in prophase of meiosis 1 until ouberty –> once a month one will finish meiosis – it doesn’t go to meiosis to until fertlized
- Seperate teh goods to one egg cell and teh rest become polar bodies
NDJ in mitosis
MDJ can occur in mitosis –> leads to chromosomal Mosaism – NDJ during anaphase of mitosis can cause some cells (liek cancer cells) to have different karyotype than other cells
Mitosis = can lead to annueploidy TOO
JDJ in mitosis + bilateral development
NDJ in mitosis with bilateral development can leave one side of the body to develope as male and the other side as female –> Some cells male on one side of body and some cells female on the other side of the body
- Mitsosi = can lead to aneuploidy
Result: Gyandromorphes
Gynadromoprhs
Organisms made up of half male and half female tissues
Development of Hyandromoprhs
Mitosis NDJ for sex chromsomes in species with bilateral development can leave one side of the body to develop as male and the other side female
ex. A cardinal was spotted in PA
Preclass
Look at pre-class notes
