L15 Chromosome abnormalities & cytoplasmic inheritance

Question 1

what is aneuploidy

Answer 1

abnormal number of chromosomes

Question 2

what are the 3 types of aneuploidy and their characteristics

Answer 2

monosomy - loss of single chromosome (2n-1)

trisomy - an extra chromosome (2n+1)

tetrasomy - an extra pair of chromosomes (2n+2)

Question 3

whats the normal human karyotype

Answer 3

males - 46, XY
femlaes 46, XX

Question 4

what is non-disjunction

Answer 4

mistakes during meiosis that give aneuploid gametes

Question 5

what happens in non-disjuction in meiosis 1

Answer 5

both pairs of chromosomes go to one side, and none of this chromosome go to the other daughter cell

forms 2 gametes w/ extra chromosome and 2 w/ missing chromosome

see onenote

Question 6

what happens in non-disjunction in meiosis 2

Answer 6

1 division is normal

but in seperation of sister chromatid, one doesnt seperate

forms a daughter cell w/ an extra
a daughter cell w/ a missing
and 2 normal

see onenote

Question 7

what % of human conceptions are aneuploid and how many of these are live births

Answer 7

20-50% aneuploidy

less than 0.5% make it to birth

Question 8

which autosomal aneuploidy is inviable

Answer 8

all monosomies
(2n-1) are inviable

Question 9

what is trisomy 21

Answer 9

down syndrome

Question 10

what is trisomy 13 and 18

Answer 10

Patau syndrome & Edwards syndrome
(die few months after birth)

the numbers 13 and 18 relate to the chromosome that they affect

Question 11

what’s the name of the test offered to women at 11-14 weeks

Answer 11

combined test

Question 12

what’s the name of the test offered to women at 14-20 weeks

Answer 12

quadruple test

Question 13

what do these tests do

Answer 13

assesses the RISK of developing aneuploidy, and if its higher than 1 in 150 then theyre offered a diagnostic test

Question 14

what are the 2 methods to get cells from the fetus

Answer 14

chorionic villus sampling (CVS)
or
amniocentesis

Question 15

after these cells are extracted, what can they do

Answer 15

culture the cells and and can determine the karyotype from this

Question 16

what has recently been developed to improve this process

Answer 16

non-invasive prenatal testing (NIPT)
looks at foetal dna in mums blood

Question 17

what is robertsonian translocation

Answer 17

another cause of down syndrome

chrom 21 and chrom 14

CARRIER - have normal chrom 14 and 21

translocation occurs, but carrier remains unaffected cuz they still have the same number of chromosomes

but they can pass down too many copies of chrom 21
causing downs in the offsprins

icl i dont rly get this but onenote ig
just know the name of it as another cause of downs
it is what it is

Question 18

what is genetic mosaiscism

Answer 18

mix of normal cells and trisomy 21 cells

• comes from when embryo w/ trisomy 21
  but then during early divisions
  it loses the extra chromosome via non-disjunction

so depending on when and where this occurs, some individuals have many cells w/ trisomy and other have less

Question 19

aneuploidy in sex chromosomes - the condition caused by monosomy in women

Answer 19

Tuner sydrome
or
XO
so one X is missing

sterile, short stature, learning difficulties

Question 20

aneuploidy in sex chromosomes - XXY result

Answer 20

47,XXY

sterile males, feminised physique, majority not diagnosed

Question 21

aneuploidy in sex chromosomes - what is Triplo-X
kinda obvs

Answer 21

47, XXX
female w/ extra X
mostly normal, may have some effect on fertility and intelligence
so most undiagnosed

Question 22

aneuploidy in sex chromosomes - what is characteristics of XYY syndrome

Answer 22

fertile males
above avg height
majority not diagnosed

Question 23

how does the mums age affect the risk of trisomy

Answer 23

the older the highe the risk of the child having trisomy

this is largely responsible as to why older women have higher rist of miscarriage

Question 24

why are older women more at risk of trisomy

Answer 24

mostly due to non-disjunction at meiosis 1

but happens more because of loss of cohesion over time

since egg is formed before birth, cohesin (like glue between chromosomes) wears down

see onenote for more detail and diagram

so its more likely to form

Question 25

what 2 places other than nucleus can dna be found in cell

Answer 25

mitochondira
chloroplast

Question 26

what are the prokayotic features of these extranuclear genomes

Answer 26

they have circular DNA

and ribosomes of mitochondria and chloroplast are diff to the others in cytoplasm
and are sensitive to bacterial antibiotics

Question 27

what do these prokaryotic features suggest about these structures

Answer 27

the endosymbiont theory

host cell = archaebacteria
a bacterial cell engulfed by host cell, and then this became the mitochondria

and then a second event of a photosynthetic prokaryote being engulfed, becoming the chloroplast

see onenote

Question 28

what genes does mtDNA have in it

Answer 28

mainly components for translation (e.g. tRNAs and rRNAs)
and
structural genes for proteins involved in oxidative phosphorylation (so like all the enzymes and stuff)

Question 29

how do we know that genes have transferred from mtDNA to the nuclear genome

Answer 29

the mtDNA is much smaller than what it would’ve originally been in the bacteria

Question 30

what genes does cpDNA have in it

Answer 30

similar to mtDNA

codes for proteins involved in translation
and
structural genes involved in photosynthesis

Question 31

what’s diff about the inheritance of mt and cp

Answer 31

they are only passed down from the mother and not the father

Question 32

what contributes to maternal inheritance of the mt genome

Answer 32

eggs are larger than sperm
so egg would have >100,000 copies of mtDNA
sperm

and

egg has mechanism for destroying mtDNA in the sperm, so it’s destroyed after fertilisation

Question 33

what does a pedigree look like for mt disease

Answer 33

females transmit the trait tom all their children
males never transmit the trait

Question 34

how does mtDNA disease present in families

Answer 34

highly variable even within one family
same mutation amy cause diff signs and symptoms

Question 35

whats the reason for the high level of variation in mtDNA disease

Answer 35

heteroplasmy

individual is carrying diff forms of mt with diff mtDNA
so a mosaic of normal and mutated mtDNA

so during segregation of mt in cell division, diff proportions of mutant mt are passed down

see onenote

Question 36

mt replacement therapy (or three person baby)

Answer 36

maternal spindle transfer:

egg from mum w/ abnormal mt

donor egg w/o mtDNA disase

mothers nucleus (chromosomes and spindle) removed
donor egg denucleated

mums egg put inside donor egg and fertilised

Question 37

whats the concerns that have come from this procedure

Answer 37

sometimes the mothers diseased mt also get transferred to the donor egg