Monday, October 30, 2006

Mid-Week Activities

I've just read over your mid-quarter evaluations, and I'm going to try to incorporate some of your requests for additional study material here in the blog. Now, many of you KNOW that all the Bio93 discussion leaders have pages and pages of worksheets you can use to study from. But you seem to be lacking in motivation. So... here's a sample problem for you to think about.

Which of the following is true of a species that has a chromosome number of 2n = 16?
A) The species is diploid with 32 chromosomes.
B) The species has 16 sets of chromosomes.
C) There are 8 homologous pairs.
D) During the S phase of the cell cycle there will be 32 separate chromosomes.
E) A gamete from this species has 4 chromosomes.

The first three students to give the right answer (with some justification) will get special mention in the next post. After 10 posts to this or any other blog posting, I will put up another question. Have your own question you want answered? Email me at adriw@... usual uci.edu

16 comments:

cmcooper said...

c. There are 8 homologous pairs. -Chelsea Cooper

Anonymous said...

c. there are 8 homologous pairs
navid

Jackie Gallardo said...

There are eight homolous pairs because n=8.

Anonymous said...

c there are 8 homologous pairs
Stephanie Giang

Adrienne Williams said...

C seems to be a popular answer. What is wrong with the others, especially D?

Anonymous said...

I believe that it is 8 homologous pairs since the homologous pairs would suggest there are 16 chromosomes. Also, the 2n would suggest diploid meaning there is two copies of each chromosomes. In this case, there are 8 homologous pairs meaning two copies of each chromosome. Brian Nguyen (1 friday disscussion) btw, c i spopular cuz it makes sense

Anonymous said...

oh ... and it is because there are are 16 chromosomes but each chromosomes has a homologous pair (which carry genes controlling the same inherited character. one from dad and one from mom. For examples genes for eye color are in the same pair of homologous chromosomes)therefore 2n=16 and one form each set so n=8.
Navid

Anonymous said...

[A] is wrong; 2n already indicates a diploid organism with 16 chromosomes, so there is no need to double the number again to become 32.
[B] is wrong; no natural organism has more than 2 sets of chromosomes, a maternal set and a paternal set.
[D] is wrong; when chromosomes replicate during meiosis (and mitosis), they are known as sister chromatids, not individual separate chromosomes.
[E] is wrong; a gamete (a haploid) of this organism will have 8 chromosomes, which is half of the diploid chromosome number.

This leaves [C] as the correct answer: There are 8 homologous pairs, which is not to be confused with 8 chromosomes.

Is this right, Dr. Williams?

Anonymous said...

C-there are 8 homologous pairs ->n=8

-Nancy Wong

Anonymous said...

choice d is wrong because although in some sense (and by some older authorities for example Dr. Edinger .. lol) each duplicate pair might be considered two chromosomes, modern usage calls on us to consider the duplicated unit, still joined at its centromere as one chromosome.
Navid

Anonymous said...

also choice (D) says, "During the S phase of the cell cycle there will be 32 separate chromosomes." which is very worng to say "separate chromosomes".
threre are 16 pair of sister chromatids or 32 sister chromatids. or just 16 chromosmes.
Navid

Anonymous said...

A. wrong because according to 2n=16, the number of chromosomes is 16
B. wrong because if there are 16 chromosomes total, it means that there must be 8 sets of chromosomes
C. right because with 8 sets of homogolous pairs, you would get 16 chromosomes total, according to 2n=16
D. wrong because DNA replication in the S phase would create not separate chromosomes but sister chromatids
E. wrong because a gamete from this species would have 8 chromosomes, due to Meiosis, which reduces the number of chromosomes in the gametes by half

-Teresa Ung (Fri @1)

Anonymous said...

Which of the following is true of a species that has a chromosome number of 2n = 16? D.
A) The species is diploid with 32 chromosomes. No (2n means it is
currently diploid which is given it has 16)
B) The species has 16 sets of chromosomes. (Nope, it has half the number
of sets). Only 8 sets but sixteen chromatids
C) There are 8 homologous pairs. (For this species, it only have 4
homogologus pairs (Each homogolous pair has two sister chromatids.) (So it would only have 4 of the homogolous pair)
D) During the S phase of the cell cycle there will be 32 separate chromosomes. (True, cell replicates and provides enough material for two times 2n (so 4 n) which is 32.
E) A gamete from this species has 4 chromosomes. (No-- Gamete formation has only n chromosomes = 8.)
Jesse jitt

Anonymous said...

(c) there are 8 homologous pairs. all others don't have make sense. 2n=16, so n=8. that's the only one that is reasonable.

anh luong (fri@1)

Anonymous said...

C. there are 8 homologous pairs
- Tiffany Vo

Adrienne Williams said...

There are many good explanations listed above. If a comment came up with "c" as the right answer, the explanation is good. Some final points to retain for the exam:

1. Humans and most animals are diploid (2n), which means they got one of each homologous chromosome from each parent. But this is not always true. Many plants are triploid or tetraploid. There are triploid lizards that must reproduce asexually. Male honeybees are haploid, and hatch from unfertilized eggs.

2. During the S phase of mitosis or meiosis, the amount of DNA is doubled, but the number of chromosomes do not change. Humans have 46 single-stranded chromosomes in G1 and 46 double-stranded chromosomes in G2. If the cell goes through mitosis, the daughter cells end up with 46 single-strand chromosomes. If the cell goes through meiosis, the four daughter cells end up with 23 single-strand chromosomes.
Enough! We'll do more in discussion.