lecture 15 Flashcards
What is the physical basis of the Mendelian law of heredity?
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
describe when chromosomes discovered
late 1800s
many microscopists observed chromosomes
in 1880 = proposed that they were physical substrate for inheritance of traits
describe chromosomes
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
the way chromosomes behaved resembles what
similar to traits
sorting
describe chromosome - physically
condensed chromosome getting ready for cell division
decondensed dna and protein that make up chrom
what is different between strawberries
for trait of size = selected over gens for bigger size
8n = big = octoploids
8 sets of chroms instead of sn
what do banana and watermelon have in common
both sterile = seedless
have odd number of sets of chrom
no fertile seeds
describe chromosome vocab
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)
describe human karyotype
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,
where is polyploidy common
common in plants = selected for over time for trait to become produce = commercial crops
uncommon in animals = arent viable, often leads to inviability
what are consequences of polyploidy
in germline = eggs and sperm, haploid cells give rise to next gen
in soma = rest of cells in body
describe somatic consequences of autopolyploidy
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
describe germline consequences of autopolyploidy
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
why are triploid sterile
goes back to how chromosomes segregate
why are we looking at meiosis
bc thats where seeds come from
review of mitosis and meiosis
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
Meiosis in diplods
cells have already replicated chroms
germ cell is diploid
meiosis 1 = chroms segregate
meiosis 2 = sister chromatids separate
meiosis 1 in triploids
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
meiosis 2 in triploids
line up on metaphase plate and segregates
gametes = each 1n but has extra chrom
all aneuploid
1n + 1
1n + 1
1n - 2
1n + 2
describe meiosis in triploids alt
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
how else can normal euploids gametes be generated in a triploid
if all extra chroms segregate by chance to same daughter cell
each goes to another cell
What is the probability of a euploid gamete
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
describe meiosis in tetraploids
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
watermelon with black seeds
4n
viable diploid gametes
can give rise to viable offspring
what causes autopolyploidy
how do they get extra set = can be elected or spontaneous
describe spontaneous autopolyploidy
Fertilization by multiple sperm = dispermy, atypical fertilization
describe induced/intentional autopolyploidy
generated intentionally
Disruption of chromosome segregation (plants)
fertilization by a diploid germ cell from a tetraploid plant
can do controlled breeding to generate autopolyploidy
how can polyploidy be generated
through selective breding
4n parent + 2n parent = diploid gamete and monoploid gamete = together makes triploid gamete
cross between 2n and 4n parent
What happens once we have this triploid watermelon plant?
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
Where did the tetraploid plant come from?
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
