lecture 15

Question 1

What is the physical basis of the Mendelian law of heredity?

Answer 1

pea plant - physical traits inherited in specific pattern
segregation, expected/predicted trait patterns
didnt know what it physically was
now we know = carried on chromosomes - dna

Question 2

describe when chromosomes discovered

Answer 2

late 1800s
many microscopists observed chromosomes
in 1880 = proposed that they were physical substrate for inheritance of traits

Question 3

describe chromosomes

Answer 3

occur in matched pairs - 2 similar
chromo some = colour body, darkly stained
chrom pairs segregate 1:1 in meiosis
segregate independently
segregation pattern correlates with inheritance of traits
correct number of chromosomes required for development

Question 4

the way chromosomes behaved resembles what

Answer 4

similar to traits
sorting

Question 5

describe chromosome - physically

Answer 5

condensed chromosome getting ready for cell division
decondensed dna and protein that make up chrom

Question 6

what is different between strawberries

Answer 6

for trait of size = selected over gens for bigger size
8n = big = octoploids
8 sets of chroms instead of sn

Question 7

what do banana and watermelon have in common

Answer 7

both sterile = seedless
have odd number of sets of chrom
no fertile seeds

Question 8

describe chromosome vocab

Answer 8

ploidy = how many sets of chroms animal cell has
normal euploid = full set chrom, strawb
abberant euploids = mono tri and tetra ploids = banana
polyploidy = extra sets of chroms
autopolyploidy = extra set of chromosomes like banan and strawb
allopolyploidy = sets from diff sources = like hybrid plants
anueploid = extra chromosomes but not full set = monosomic (2n-1) and trisomic (2n+1)

Question 9

describe human karyotype

Answer 9

diploid, euploid = 46 chrom, 2n = 23 in each set
Abnormal = euploid, not viable tho since has 3 sets of chromosomes = each is a set of 3
anueploid = 3 copies of ONE crhom so trisomic,

Question 10

where is polyploidy common

Answer 10

common in plants = selected for over time for trait to become produce = commercial crops
uncommon in animals = arent viable, often leads to inviability

Question 11

what are consequences of polyploidy

Answer 11

in germline = eggs and sperm, haploid cells give rise to next gen
in soma = rest of cells in body

Question 12

describe somatic consequences of autopolyploidy

Answer 12

increased size - strawbs, parts of watermelon plant-individual parts of plants are larger, leaves and flowers
lethality = rare in animals to see polyploidy = when happens, not viable, happens in pregnancy but leads to miscarriage, not often later in pregnancy

Question 13

describe germline consequences of autopolyploidy

Answer 13

have no seeds = sterile - since gametes that produce seeds are aneuploid
gametes also are not viable = seedless, *Ex = oysters cultivated to be sold = germline doesnt develop so tastes better

Question 14

why are triploid sterile

Answer 14

goes back to how chromosomes segregate

Question 15

why are we looking at meiosis

Answer 15

bc thats where seeds come from

Question 16

review of mitosis and meiosis

Answer 16

mitosis = dna rep –> metaphase plate –> segregate –> 2 diploid daughter cells
Meiosis = 2 rounds, same steps as mitosis but sister chromatids segregate to 4 diff daughter cells all haploid

Question 17

Meiosis in diplods

Answer 17

cells have already replicated chroms
germ cell is diploid
meiosis 1 = chroms segregate
meiosis 2 = sister chromatids separate

Question 18

meiosis 1 in triploids

Answer 18

extra set of chrom = 3 sets
= leads to 4 chroms in one cell and 3 in other cell instead of 3 in each
cannot give everyone the same and the extra chrom cannot pair

Question 19

meiosis 2 in triploids

Answer 19

line up on metaphase plate and segregates
gametes = each 1n but has extra chrom
all aneuploid
1n + 1
1n + 1
1n - 2
1n + 2

Question 20

describe meiosis in triploids alt

Answer 20

also by chance all can go to same daughter cell = leads to euploid gametes =
3 chroms and 5 chroms
leads to 1n 1n and 2n 2n
cell is viable but doesnt mean it gives viable offspring

Question 21

how else can normal euploids gametes be generated in a triploid

Answer 21

if all extra chroms segregate by chance to same daughter cell
each goes to another cell

Question 22

What is the probability of a euploid gamete

Answer 22

p(euploid) = think about probably of each
1 x 1/2 x 1/2 = 1/4
p= (0.5)^n-1 = even with only 3 or 4 chroms = # of haploid gametes v low, neg impact on fertility

triploids rarely produce euploid gametes
p=(0.5)^10 = 1/1024 = gives rise to gamete that has potential to form seed and fertilize another seed, v low tho

Question 23

describe meiosis in tetraploids

Answer 23

pairs will segregate
4 sets chrom = every chrom pair
start with 2 sets of 3 chroms = 4n
leads to each cell being 2n = all diploid gametes, in plant its viable

Question 24

watermelon with black seeds

Answer 24

4n
viable diploid gametes
can give rise to viable offspring

Question 25

what causes autopolyploidy

Answer 25

how do they get extra set = can be elected or spontaneous

Question 26

describe spontaneous autopolyploidy

Answer 26

Fertilization by multiple sperm = dispermy, atypical fertilization

Question 27

describe induced/intentional autopolyploidy

Answer 27

generated intentionally
Disruption of chromosome segregation (plants)
fertilization by a diploid germ cell from a tetraploid plant
can do controlled breeding to generate autopolyploidy

Question 28

how can polyploidy be generated

Answer 28

through selective breding
4n parent + 2n parent = diploid gamete and monoploid gamete = together makes triploid gamete
cross between 2n and 4n parent

Question 29

What happens once we have this triploid watermelon plant?

Answer 29

sterile = arent producing seeds so cannot grow more
watermelon growers take 4nx2n and takes gametes and generates triploid = always have to cross to produce seedless watermelon

Question 30

Where did the tetraploid plant come from?

Answer 30

mitosis in diploid = 2n=4
in lab = each segregated to daughter cell =

normal = 2 diploid cells
will colchicine = on tetraploid 4n=8 - want chrom to stay in same cell, colchicine = chemical that disrupts microtubules = cellular motors that pull chrom to diff cells during segregation and cell wont divide, cell then grown to generate mature plant = can cultivate and treat and grow into plant
if do another round = will end up with 8n

cell grown to generate a mature 4n plant from 2n cells – colchicine –> cell grown to generate mature 8n plant, double # of chroms