What is a tetrad?

Question

I'm reading about synapsis and tetrads in Prophase I, and in the picture it has two sister chromatids, and I don't understand how there are 4 total chromosomes, so that when in Anaphase, splitting occurs in meiosis, each new cell has one chromosome from each homologous pair. Why wouldn't it have two? I know tetra means 4, but I don't understand how this works. Isn't a homologous chromosome singular?

Answer 1

Tetrad means four chromatids.
This situation can be seen when each chromosome with two chromatids, lines up with its homologous chromosome(having two chromatids) along the equatorial plate. Thus the pair of chromosome has in total four chromatids.

Answer 2

The term "tetrad" is referring to the 4 chromatids present in the two replicated chromosomes that associate during prophase I of meiosis. Once crossing over has happened, the 4 chromatids are all genetically distinct from each other. During anaphase I, remember that the homologous chromosomes separate from each other. The two daughter cells after meiosis I are technically still diploid, if you think about having copies of each gene. But, at that point, those two chromatids make up a single chromosome, and so the cells actually have a haploid chromosome number. I know it's confusing...

Answer 3

Tetrad Chromosome

Answer 4

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RE:
What is a tetrad?
I'm reading about synapsis and tetrads in Prophase I, and in the picture it has two sister chromatids, and I don't understand how there are 4 total chromosomes, so that when in Anaphase, splitting occurs in meiosis, each new cell has one chromosome from each homologous pair. Why...

Answer 5

A tetrad is formed when two homologous chromosomes line up side by side (synapse). Each homologous chromosome has two sister chromatids held together at the centromere. So the tetrad has four chromatids all together.

One homologous chromosome is singular- it is one chromosome. However, it has two sister chromatids because the DNA in the chromosome was duplicated during the S stage of interphase before meiosis began.

Here's a diagram of a tetrad formed by two synapsed homologous chromosomes. I suspect that all the terminology is mixing you up, but pictures help sometimes.
http://www.cabinsoftware.biz/Genetics_Tutorial/Image23.gif

Answer 6

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A. prophase I That's when the chromosomes are condensed from chromatin and the homologous chromosomes synapse. They line up on the equator of the spinde during metaphase I, and they are already synapsed into tetrads at that point, so they formed the tetrads during prophase I.

Answer 7

A. Prophase I of meiosis. Although they remain tetrads up until anaphase I of meiosis. A tetrad refers to the lining up of homologous, replicated chromosomes (tetra is four in Greek).

Answer 8

You probably think of a chromosome as a "X", but that's really a chromosome that's already replicated (sister chromatids) - think of this as a ">" and an "<" held together by a centromere. So it's really two identical chromosomes.

So when you're seeing the X X in prophase I, what you really have are two of ">" and two of "<" (>< and ><). The four chromosomes together makes the tetrad (tetra means 4) and you have two SETS of sister chromatids.

The first split Telophase I gives you >< (one set of sister chromatids) in one cell and >< (the other set of sister chromatids) in the other.

In Telophase II, the cells divide again into >, <, >, <, so each daughter cell has a single chromosome.