Mitosis/cell cycle questions

Hi its me again - the one with the shocking unit 1 teacher lol. Was given a large booklet with various past exam questions on it - i have done nearly all the ones on the actual cell cycle because i can teach myself it - but the follwing i need help on (positive rep will be rewarded but it wont count for much...)

a) There are 18 chromosomes in the somatic (body) cells of a cabbage. How many chromosomes would be present in eeach of the following?

(i) male nucleus in the pollen grain.

(ii) a cell in anaphase of mitosis.

(iii) a cell in anaphase I of meiosis

(iv) a cell in anaphase II of meiosis

(b) the diploid chromosome number of the radish is also 18 chromosomes.

(i) How many chromosomes would there be in a diploid nucleus of the hybrid offspribf produced by crossing a cabbage with a raddish. Show your working

(this is probably all easy but i am stumped as all of this is new to me)

(ii) Suggest why such a hybrid would infertile. (2)

Thanks in advance

Regards, Asad

Reply 1

Revenged

15

asadtamimi

Hi its me again - the one with the shocking unit 1 teacher lol. Was given a large booklet with various past exam questions on it - i have done nearly all the ones on the actual cell cycle because i can teach myself it - but the follwing i need help on (positive rep will be rewarded but it wont count for much...)

a) There are 18 chromosomes in the somatic (body) cells of a cabbage. How many chromosomes would be present in eeach of the following?

(i) male nucleus in the pollen grain.

(ii) a cell in anaphase of mitosis.

(iii) a cell in anaphase I of meiosis

(iv) a cell in anaphase II of meiosis

(b) the diploid chromosome number of the radish is also 18 chromosomes.

(i) How many chromosomes would there be in a diploid nucleus of the hybrid offspribf produced by crossing a cabbage with a raddish. Show your working

(this is probably all easy but i am stumped as all of this is new to me)

(ii) Suggest why such a hybrid would infertile. (2)

Thanks in advance

Regards, Asad

i) 9 chromosome (gamete thus has half the number of chromosomes)

ii) 36 chormosomes (DNA has replicated, so double number of chromosome)

iii) 36 chromosomes (same as ii)

iv) 18 chromosomes (half the chromosomes as in iii) because chromosomes split by cytokinesis, which is the spliting of the cytoplasm, after meiosis I)

b) i) think it's just... 9 chromosome in each of the gametes and so there will be a total of 18 chromosomes in the new organism formed

ii) chromosomes aren't going to be able to form homologous pairs of chomosomes because they originate from different offspring and so you can't have them forming homologous pairs in prophase I of meiosis. Thus meiosis cannot take place, you cannot produce gametes and the organism is infertile.

Reply 2

asadtamimi

OP

13

Revenged

i) 9 chromosome (gamete thus has half the number of chromosomes)

ii) 36 chormosomes (DNA has replicated, so double number of chromosome)

iii) 36 chromosomes (same as ii)

iv) 18 chromosomes (half the chromosomes as in iii) because chromosomes split by cytokinesis, which is the spliting of the cytoplasm, after meiosis I)

b) i) think it's just... 9 chromosome in each of the gametes and so there will be a total of 18 chromosomes in the new organism formed

ii) chromosomes aren't going to be able to form homologous pairs of chomosomes because they originate from different offspring and so you can't have them forming homologous pairs in prophase I of meiosis. Thus meiosis cannot take place, you cannot produce gametes and the organism is infertile.

thanks a lot - i missed one out :

(v) a nucleus in telophase II of meiosis

Reply 3

Revenged

15

asadtamimi

thanks a lot - i missed one out :

(v) a nucleus in telophase II of meiosis

v) 9 chromosome

Reply 4

asadtamimi

OP

13

Revenged

v) 9 chromosome

Thanx - can i annoy you with a couple more questions lol....

b) If the amount of DNA present in the cell at metaphase is 20 units, how much DNA will be present in each nucleus :

i() at the start of prophase

I think this is 10 because its before DNA replication?

(II) immediately after telophase

I think 10 because they split up?

Also name two precise locations where mitosis occurs in plants?

Thanx in advance :biggrin:

Reply 5

MadNatSci

12

asadtamimi

Thanx - can i annoy you with a couple more questions lol....

b) If the amount of DNA present in the cell at metaphase is 20 units, how much DNA will be present in each nucleus :

i() at the start of prophase

I think this is 10 because its before DNA replication?

(II) immediately after telophase

I think 10 because they split up?

Also name two precise locations where mitosis occurs in plants?

Thanx in advance :biggrin:

Prophase immediately follows replication: DNA replication takes place in S phase, which is part of "interphase" for A level purposes I believe! So there would be 20 units of DNA at prophase. (To clarify: in prophase you basically just get condensation of the DNA: it's all already replicated.)

I think you're right about the telophase one though - the nuclear envelopes should have reformed around the two sets of chromosomes so you have two nuclei, though I'm not sure the actual cell would have divided (cytokinesis) at that point.