lecture 16 Flashcards
name the 2 ways triploidy can be generated
defective meiosis
dispermy
explain triploidy generated through defective meiosis
plant or animal cell - failure in segregation = all chroms in gamete, 2n + 1n = 3n gamete
generally = failures in basic cellular processes can lead to defects or diversity
triploidy not viable in humans - common cause is mistake in meiosis so one diploif and when fertlized makes triploid
explain triploidy generated through dispermy
fertilization of egg with 2 sperms
3n
triploid zygote
infrequent, usually fertilization prevents 2nd sperm entering egg
most common cayuse of human triploidy
hypothesis= crowded petshop conditions lead to dispermy = crowded
invasive crayfish - doesnr need to mate to reproduce, can just keep reproducing on own= parthenogenic
what is autopolyploid
individual that has multiple chromosome sets originating from within one species
what is allopolyploid
individual that has mutiple chrom sets originating from 2 or more diff species
like hybrid so gametes from diff species
describe generation of allopolyploid
radish - eat root part
raphanus 2n=18
cabbage = eat part above ground
brassica 2n=18
cross together = n+n = 18, so 2n= 18
sterile f1 hybrid
why sterile = might not have all the genes its needs to reproduce since 2 diff sets of chroms, coming from species = maybe dont pair and cannot segregate properly
why is autopolyploid hybrid sterile
2 sets = too diff to pair during meiosis
leads to defect segregation = anueploid gametes
describe generation of autopolyploid that is fertile
if spontaneous doubling of chroms = leads to fertile amphidiploid, raphanobrassica
genome doubled so 2 of each
= can pair, has partner, so then can segregate
leads to opp phenotype tho
describe crossing an allopolyploid back to one of its parent species
raphanobrassica = 2n+2n= 4n = 36, nr nb
crosses by brassica 2n=18, nb
f1 = nr nb nb = unequal (nr cant pair) segregation since unequal number of chrom = aneuploid, not viablE
no F2, since f1 sterile
these 2 plants cannot breed = new species, reproductively isolated from species that produced it
describe origin of 3 allopolyploid species of brassica
happened many times
errors in basic processes = can cause negative consequences like sterility and inviability but also contributes to diversity
descrive polyploidy vs aneuploidy
polyploidy - triploidy 3n
anueploid - trisomic 2n+1
describe viable trisomies
xxx and xyy = normal
xxy = klinefleter syndrome = some physical characteristics
trisomy 21 = down syndrome, viable, some developmental differences and physiological problems
descrive viable monosomy
X0 = turner syndrom 2n-1
one losing chrom = v severe, loss of one x, some developemental issues and physical characteristics
describe other trisomies
trisomy 13, trisomy 18 = non viable usually die in infancy
all others = non viable, dies in utero
what does aneuploidy affect
Balance of gene dosage in a cell
A:B 1:1 in all euploids
eg = triploid 3:3= 1:1
2 doses of each gene in cell
out of balance
not right amount
Imbalanced
describe human trisomy 21
only trisomy to routinely survive adulthood
phenotypes of partial trisomy 21s help identify which regions contribute to down syndrome
describe trisomics of datura (jimsonweed)
plants more tolerant to changes
n = 12
2n, 2n+ 1, each = diff type of it
diff chroms have diff info
makes seed product abnormal but in diff ways = depends on which chrom it is
gene dosage experiment
describe number of chrom in trisomic echinus variant
n = 12
leaf cells = 2n = 24
trisomic leaf cells = 2n+1= 25
descrive germline consequences of aneuploidy
3 copies, 3 possible configurations in meiosis 1
= 6 possible gametes
equal proportions of any combos of 3 chroms
how does aneuploidy arise
results from abnormal segregation of homologous chromosomes during meiosis
ex = unpaired chroms during meiosis in triploid individuals - frequent,
3rd set of chrom must segregate = 1n+2 and 1n+1
what is non disjuction and explain
failure of chromosomes to properly segregate during anaphase
ex = non distinction of homologous chroms during meiosis in diploid indivduals = rare
can happen during mitosis
can happen during either meiosis 1 or 2
describe non disjunction during meiosis 1
extra chrom goes to one cell in meiosis 1 =
if chrom was y chrom = gives gamete with extra y chrom
4 chroms and 3 chroms
leads to 1n + 1 1n +1 1n - 1 1n-1
= 100% aneuploid gametes
describe non disjunction during meiosis 2
50% aneuploid gametes
2 normal gametes generated and 2 non normal ones
1n 1n & 1n-1 1n+1
why is trisomic plant possible if aneuploid gametes not viable
vocab - aneuploid refers to all = no viable, not in complete set but degree of viability depends on how close to normal number of chroms it has
biology - depends on plant, tolerance for aneuploidy low but some plants more tolerants like watermelon and bananas - crops that are seedless do not ahve detectable viable gametes
It depends on the plant species
Some triploids can give rise to viable aneuploids that are trisomic (i.e. with one extra chromosome) but aneuploids with multiple extra chromosomes are not normally observed
