lecture 16

Question 1

name the 2 ways triploidy can be generated

Answer 1

defective meiosis
dispermy

Question 2

explain triploidy generated through defective meiosis

Answer 2

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

Question 3

explain triploidy generated through dispermy

Answer 3

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

Question 4

what is autopolyploid

Answer 4

individual that has multiple chromosome sets originating from within one species

Question 5

what is allopolyploid

Answer 5

individual that has mutiple chrom sets originating from 2 or more diff species
like hybrid so gametes from diff species

Question 6

describe generation of allopolyploid

Answer 6

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

Question 7

why is autopolyploid hybrid sterile

Answer 7

2 sets = too diff to pair during meiosis
leads to defect segregation = anueploid gametes

Question 8

describe generation of autopolyploid that is fertile

Answer 8

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

Question 9

describe crossing an allopolyploid back to one of its parent species

Answer 9

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

Question 10

describe origin of 3 allopolyploid species of brassica

Answer 10

happened many times
errors in basic processes = can cause negative consequences like sterility and inviability but also contributes to diversity

Question 11

descrive polyploidy vs aneuploidy

Answer 11

polyploidy - triploidy 3n
anueploid - trisomic 2n+1

Question 12

describe viable trisomies

Answer 12

xxx and xyy = normal
xxy = klinefleter syndrome = some physical characteristics
trisomy 21 = down syndrome, viable, some developmental differences and physiological problems

Question 13

descrive viable monosomy

Answer 13

X0 = turner syndrom 2n-1
one losing chrom = v severe, loss of one x, some developemental issues and physical characteristics

Question 14

describe other trisomies

Answer 14

trisomy 13, trisomy 18 = non viable usually die in infancy
all others = non viable, dies in utero

Question 15

what does aneuploidy affect

Answer 15

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

Question 16

describe human trisomy 21

Answer 16

only trisomy to routinely survive adulthood
phenotypes of partial trisomy 21s help identify which regions contribute to down syndrome

Question 17

describe trisomics of datura (jimsonweed)

Answer 17

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

Question 18

describe number of chrom in trisomic echinus variant

Answer 18

n = 12
leaf cells = 2n = 24
trisomic leaf cells = 2n+1= 25

Question 19

descrive germline consequences of aneuploidy

Answer 19

3 copies, 3 possible configurations in meiosis 1
= 6 possible gametes
equal proportions of any combos of 3 chroms

Question 20

how does aneuploidy arise

Answer 20

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

Question 21

what is non disjuction and explain

Answer 21

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

Question 22

describe non disjunction during meiosis 1

Answer 22

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

Question 23

describe non disjunction during meiosis 2

Answer 23

50% aneuploid gametes
2 normal gametes generated and 2 non normal ones
1n 1n & 1n-1 1n+1

Question 24

why is trisomic plant possible if aneuploid gametes not viable

Answer 24

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

Question 25

describe progeny produced by aneuploid gametes

Answer 25

1n and 1n +1 = 1n + 1n + 1 = 2n +1 = trisomic
1n and 1n - 1 = 1n + 1n - 1 = 2n-1 = monosomic