Bio question

[darkkings13]

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Hi everyone,

This question was stated in Bootcamp, but I do not really understand the concept of it.

"If 2n=46, how many tetrads are present during metaphase 1? The answer was 23..Can you guys explain the concept behind this?

 

[dent777]

Tetrad = 2 homologous chromosomes (aka 4 chromatids) are paired and appear as one structure in Metaphase of Meiosis I. Humans have 46 chromosomes, but if you pair the homologs together you will have 23 tetrads.

 

[Jordwin]

The 2n represents diploid. A tetrad is a combination of two chromosomes, so that would divide the diploid number in half (still diploid but that's not what it's asking for).

 

[Minion]

You have to think of it this way, during Meiosis I, specifically Prophase I. The chromosomes form tetrads of nonsister chromatids. Tetrads are just two chromosomes paired up together. So it is asking during Metaphase I, which is when independent assortment will eventually happens, but not yet. So the tetrads are lined in the middle during metaphase I. Think of it like this. How many pairs can you make with 46 chromosomes? Only 23.

 

[Soleus715]

I think everyone explained it really well.

Tetra (numerical prefix for 4) refers to the amount of chromatids per tetrad.

And a diploid cell ( 2n=46 ) has 92 chromatids,

so 92 divided by 4 is 23 tetrads.

 

[darkkings13]

thanks everyone! Do you guys know how to solve the problems where it asks how many chromosomes are in anaphase? in Meiosis II Anaphase? etc..Those type of questions? I am kind of struggle with that as well..

 

[Soleus715]

The easiest way is to count the number of centromeres in each phase that it asks about. Each centromere counts as a chromosome.

More detailed explanation:

In mitosis, a 2n=46 cell would have 46 chromosomes and 92 chromatids.

When the chromosome separates, notice that the number of centromeres has doubled because each chromatid now has a centromere.

In anaphase, each chromosome separates into two chromatids. When a chromatid is by itself, it is now called a chromosome by definition. The 92 chromatids are all separated in anaphase and are ALL labeled as chromosomes. (Total of 92 chromosomes in anaphase)

In meiosis Anaphase II, It is analogous to the Anaphase in mitosis, EXCEPT that the chromosome number had been reduced from Telophase I. (46 to 23 chromosomes) Therefore, 23 chromosomes are separated into 46 individual chromatids. Remember that each chromatid now has a centromere and is labeled as a chromosome. (46 chromosomes in Anaphase II of meiosis)

Let me know if you need help with anything else 😀

 

[darkkings13]

thank you so much for the help! that really helped!..I have like one more concept question that I still need help on..and thats on Meiosis...(particularly meiosis 1 and 2) I get confused on how it works..I know that Meiosis 2 is very similar to Mitosis. If any of you guys can help, that would be great!

 

[Soleus715]

I kinda hinted at it but pretty much Meiosis II is like Mitosis with half the chromosomes.

Meiosis I differs from mitosis in that in Prophase 1 you get synapsis, or the forming of tetrads. Then chiasmata occurs where non-sister chromatids exhibit crossing over of genetic info.

Also in metaphase I/ anaphase I, you have tetrads that line up at the plate and separate into homologous chromosome pairs (NO chromatids separating here). (The end result of anaphase I is 46 chromosomes and 92 chromatids)

At the end of Telophase I, you have 23 chromosomes in each daughter cell and each chromosome has 2 sister chromatids.

Note that Meiosis I does not separate chromatids and just separates chromosomes into two daughter cells that will go into Meiosis II. This is why Telophase II is considered the chromosome reduction phase.

I hope that the end result of Telophase I helps you understand how Meiosis II is analogous to Mitosis with half the chromosomes/chromatids. This is why Meiosis II ends with 4 haploid 👎 daughter cells. (23 chromosomes in each daughter cell with 23 chromatids)