1. Introduction: Down Syndrome and Maternal Age: What’s the connection?

Source: Centers for Disease Control. Click to enlarge.

Down Syndrome is a condition that occurs in about 1 in every 700 babies born in the United States. The syndrome is characterized by

  • varying degrees of cognitive delays
  • low muscle tone
  • small stature
  • an upward slant to the eyes
  • a single deep crease across the center of the palm.
  • an “increased risk for certain medical conditions such as congenital heart defects, respiratory and hearing problems, Alzheimer’s disease, childhood leukemia, and thyroid conditions.”

(To learn more about the symptoms of Down Syndrome, please go to the National Down Syndrome Society’s website, which is also the source of the quote above).

Ninety-five percent of Down Syndrome cases are caused by an error in meiosis called nondisjunction, which results in people with Down Syndrome having an extra copy of chromosome 21, as shown below.

[qwiz style=”width: 600px !important;”]

[q] Take a minute and study the chart below. Then, on your student learning guide (or any piece of paper), write down the correlation, which you should formulate as follows: “As ________, ______.”

 

[c]IENsaWNrIHRvIHNl ZSB0aGUgYW5zd2Vy[Qq]

[f]IFlvdSBwcm9iYWJseSB3cm90ZSBzb21ldGhpbmcgbGlrZSAmIzgyMjA7QXMgbWF0ZXJuYWwgYWdlIGluY3JlYXNlcywgdGhlIGluY2lkZW5jZSBvZiBEb3duIFN5bmRyb21lIGluY3JlYXNlcy4mIzgyMjE7

Cg==

TGV0JiM4MjE3O3Mgc2VlIGhvdyBub25kaXNqdW5jdGlvbiB3b3Jrcywgc28gd2UgY2FuIGZpZ3VyZSBvdXQgd2h5IHRoaXMgaXMu[Qq]

[/qwiz]

2. Nondisjunction

Much of meiosis is about chromosomes coming together and then separating.

  • During prophase 1 (image “2,” above), homologous chromosomes come together.
  • During anaphase 1 (image “4,”, above), homologous pairs are pulled apart.
  • During anaphase 2 (image “10,” above), doubled chromosomes, consisting of two sister chromatids, are pulled apart.

Nondisjunction is the term used to describe what happens when homologous pairs or sister chromatids fail to separate in a typical way. Pulling the word “nondisjunction” apart will help you to understand and remember it.

  • Two homologs linked by a chiasma (red arrow)

    Junction: when two things come together, as in “railroad junction.”

    • During meiosis, junctions appear during prophase 1 when tetrads form. In the case of tetrads, the junctions are the chiasmata that link homologous pairs.
    • Another junction results from the duplication of chromosomes into sister chromatids that happens during interphase 1 (the interphase that precedes Meiosis I). In this case, the junction between the two sister chromatids is the centromere.
  • Disjunction: A disjunction is: “a sharp cleavagedisunion, separation, as in the disjunction between theory and practice.” (Merriam Webster). In meiosis, a disjunction is what’s supposed to happen during anaphase 1 (when homologous pairs are pulled apart) and anaphase 2 (when sister chromatids are pulled apart).
  • Nondisjunction is when the separation of homologous pairs or of sister chromatids that is supposed to happen doesn’t happen. As a result “one daughter cell has both and the other neither of the chromosomes.” (Merriam Webster)

Let’s walk through some ways in which nondisjunction can happen, and then look at the consequences.

Nondisjunction: Modified from an image created by the Bioninja

To keep things simple, we’ll use a cell with two homologous pairs (shown at “a”). Meiosis I (represented by the arrows at “1”) should separate the homologous pairs, which happens correctly in cell “g.”

But look at what happens if we follow the branch to the left. In cell “b,” the bottom homologous pair fails to separate. As a result, we have three doubled chromosomes on the left side of cell “b” and one doubled chromosome on the right.

During meiosis II (represented by arrow “2”), the sister chromatids separate. Because of the nondisjunction that happened during meiosis I, the cell on the far left (“c”) has three chromosomes that are being pulled apart (instead of two). Cell “d” has one chromosome that’s being pulled apart (instead of two).

During cytokinesis 2 (represented by the arrow at “3”) cell “c” divides to form haploid gametes. But each resulting gamete (the cells labeled “e”) will each have an extra chromosome. When cell “d” divides, the two gametes that result will be missing a chromosome.

At this point, we need to review the notation that biologists use to talk about meiosis, both when it proceeds, correctly, and when it goes awry, as in nondisjunction.

  • A diploid cell, with its two sets of chromosomes, can be referred to as “2n” (two sets).
  • A haploid cell, with one set of chromosomes, can be referred to as “n” (one set).

So, look at the two gametes labeled “e.” They should have a single set of chromosomes (n). But they have, because of nondisjunction, an extra chromosome. We annotate that as “n+1.” The two gametes at “f” are missing a chromosome, and we annotate that as “n-1.”

That’s one way that nondisjunction can happen. But if you look again at the diagram (now on your right), you can see that there’s another pathway as well. Look at cell “g.” It’s the successful product of Meiosis I (arrow “1”). However, during meiosis II (arrow “2”), sister chromatids are supposed to separate. But in cell “h,” anaphase 2 was unsuccessful, and you can see that the result is three sister chromatids on the left side of the cell, and only one on the right). When cytokinesis 2 occurs, the gamete at “j” will be n+1, while the gamete at “k” is n-1. Note that because anaphase happened correctly in cell “i” the resulting gametes at “l” both have the correct number of chromosomes: they’re haploid cells, with a chromosome number of n. Also note a hidden step that’s not shown in the diagram: the doubled chromosome in the bottom left of cell “h” separates into two, full-fledged chromosomes.

Source: Wikipedia

If a gamete with an atypical number of chromosomes (n-1 or n+1) is fertilized by another gamete with a typical number of chromosomes (n) then the resulting zygote will similarly have an extra or a missing chromosome.

  • An extra chromosome is called a trisomy: 3 chromosomes instead of a homologous pair. The cell at “3” on the left has a trisomy.
  • A missing chromosome is called a monosomy: 1 chromosome instead of a homologous pair. The cell at “4” on the left has a monosomy.

Take a look at the karyotype below:

This is trisomy 21. It’s the chromosomal cause of most Down syndrome cases, and it’s caused by a nondisjunction that occurs during meiosis.

3. Nondisjunction: Checking Understanding

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Nondisjunction (v2.0)”]

[h]Nondisjunction: Checking Understanding

[i]

[q] In the diagram below, which letter shows a cell that is “2n”?

[textentry single_char=”true”]

[c]IG E=[Qq]

[f]IEV4Y2VsbGVudC4gVGhlIGNlbGwgYXQgJiM4MjIwO2EmIzgyMjE7IGlzIGRpcGxvaWQsIG9yICYjODIyMDsybi4mIzgyMjE7[Qq]

[c]IEVudGVyIHdvcmQ=[Qq]

[f]IE5vLCB0aGF0JiM4MjE3O3Mgbm90IGNvcnJlY3Qu[Qq]

[c]ICo=[Qq]

[f]IE5vLiBGaW5kIGEgY2VsbCB0aGF0IGhhcyB0d28gc2V0cyBvZiBjaHJvbW9zb21lcy4=[Qq]

[q] In the diagram below, which letter shows a gamete that is “n + 1,” and which resulted from nondisjunction during meiosis I”?

[textentry single_char=”true”]

[c]IG U=[Qq]

[f]IEV4Y2VsbGVudC4gVGhlIGNlbGwgYXQgJiM4MjIwO2UmIzgyMjE7IGlzIG4gKyAxLCBhbmQgcmVzdWx0ZWQgZnJvbSBhIG5vbmRpc2p1bmN0aW9uIHRoYXQgb2NjdXJyZWQgZHVyaW5nIE1laW9zaXMgSSAoYmV0d2VlbiBjZWxsICYjODIyMDthJiM4MjIxOyBhbmQgY2VsbCAmIzgyMjA7Yi4mIzgyMjE7KQ==[Qq]

[c]IEVudGVyIHdvcmQ=[Qq]

[f]IE5vLCB0aGF0JiM4MjE3O3Mgbm90IGNvcnJlY3Qu[Qq]

[c]ICo=[Qq]

[f]IE5vLiBTdGFydCBieSBmaW5kaW5nIGEgZ2FtZXRlIHRoYXQgaGFzIGFuIGV4dHJhIGNocm9tb3NvbWUgKG1ha2luZyBpdCBuICsgMSkuIFRoZW4sIG1ha2Ugc3VyZSB0aGF0IHRoaXMgY2VsbCByZXN1bHRlZCBmcm9tIG5vbmRpc2p1bmN0aW9uIGR1cmluZyBNZWlvc2lzIEkgKHdoaWNoIGlzIHdoZW4gaG9tb2xvZ291cyBwYWlycyBhcmUgc3VwcG9zZWQgdG8gc2VwYXJhdGUpLg==[Qq]

[q] In the diagram below, which letter shows a gamete that is “n – 1,” and which resulted from nondisjunction during Meiosis II”?

[textentry single_char=”true”]

[c]IG s=[Qq]

[f]IEV4Y2VsbGVudC4gVGhlIGdhbWV0ZSBhdCAmIzgyMjA7ayYjODIyMTsgaXMgbiAmIzgyMTE7IDEsIGFuZCByZXN1bHRlZCBmcm9tIGEgbm9uZGlzanVuY3Rpb24gdGhhdCBvY2N1cnJlZCBkdXJpbmcgTWVpb3NpcyBJSSAoYmV0d2VlbiBjZWxsICYjODIyMDtnJiM4MjIxOyBhbmQgY2VsbCAmIzgyMjA7aC4mIzgyMjE7KQ==[Qq]

[c]IEVudGVyIHdvcmQ=[Qq]

[f]IE5vLCB0aGF0JiM4MjE3O3Mgbm90IGNvcnJlY3Qu[Qq]

[c]ICo=[Qq]

[f]IE5vLiBTdGFydCBieSBmaW5kaW5nIGEgZ2FtZXRlIHRoYXQgaGFzIGEgbWlzc2luZyBjaHJvbW9zb21lIChtYWtpbmcgaXQgbiAmIzgyMTE7IDEpLiBUaGVuLCBtYWtlIHN1cmUgdGhhdCB0aGlzIGNlbGwgcmVzdWx0ZWQgZnJvbSBub25kaXNqdW5jdGlvbiBkdXJpbmcgTWVpb3NpcyBJSSAod2hpY2ggaXMgd2hlbiBzaXN0ZXIgY2hyb21hdGlkcyBhcmUgc3VwcG9zZWQgdG8gc2VwYXJhdGUpLg==[Qq]

[q] In the diagram below, which letter shows gametes that, when fertilized, will produce a zygote with a trisomy? (Choose one of the two possible answers and enter it below)

[textentry single_char=”true”]

[c]IGU7 IGo=[Qq]

[f]IEV4Y2VsbGVudC4gVGhlIGNlbGxzIGF0ICYjODIyMDtlJiM4MjIxOyBhbmQgJiM4MjIwO2omIzgyMjE7IGFyZSBuICsgMS4gV2hlbiBmZXJ0aWxpemVkIGJ5IGFub3RoZXIgZ2FtZXRlIHRoYXQgaGFzIG9uZSBoYXBsb2lkIHNldCBvZiBjaHJvbW9zb21lcyAobiksIHRoZSByZXN1bHRpbmcgZ2FtZXRlcyB3aWxsIGhhdmUgYSB0cmlzb215Lg==[Qq]

[c]IEVudGVyIHdvcmQ=[Qq]

[f]IE5vLCB0aGF0JiM4MjE3O3Mgbm90IGNvcnJlY3Qu[Qq]

[c]ICo=[Qq]

[f]IE5vLiBTdGFydCBieSBmaW5kaW5nIHRoZSBnYW1ldGVzIHRoYXQgaGF2ZSBhbiBleHRyYSBjaHJvbW9zb21lIChtYWtpbmcgdGhlbSBuICsgMSku[Qq]

[q] In the diagram below, which letter shows cells that, when fertilized, will produce a zygote with monosomy? Choose one of the two possible answers and enter it below)?

[textentry single_char=”true”]

[c]IGY7 IGs=[Qq]

[f]IEV4Y2VsbGVudC4gVGhlIGNlbGxzIGF0ICYjODIyMDtmJiM4MjIxOyBhbmQgJiM4MjIwO2smIzgyMjE7IGFyZSBuICYjODIxMTsgMS4gV2hlbiBmZXJ0aWxpemVkIGJ5IGFub3RoZXIgZ2FtZXRlIHRoYXQgaGFzIG9uZSBoYXBsb2lkIHNldCBvZiBjaHJvbW9zb21lcyAobiksIHRoZSByZXN1bHRpbmcgZ2FtZXRlcyB3aWxsIGhhdmUgYSBtb25vc29teSAodGhleSYjODIxNztsbCBiZSBtaXNzaW5nIGEgY2hyb21vc29tZSku[Qq]

[c]IEVudGVyIHdvcmQ=[Qq]

[f]IE5vLCB0aGF0JiM4MjE3O3Mgbm90IGNvcnJlY3Qu[Qq]

[c]ICo=[Qq]

[f]IE5vLiBIZXJlJiM4MjE3O3MgYSBoaW50OiB5b3UgbmVlZCB0byBmaW5kIGEgZ2FtZXRlIHRoYXQgaGFzIGEgbWlzc2luZyBjaHJvbW9zb21lIChtYWtpbmcgaXQgbiAmIzgyMTE7IDEpLg==[Qq]

[q] In the diagram below, which number or letter represents Meiosis I?

[textentry single_char=”true”]

[c]ID E=[Qq]

[f]IEV4Y2VsbGVudC4gTnVtYmVyICYjODIyMDsxJiM4MjIxOyByZXByZXNlbnRzIE1laW9zaXMgSSwgd2hpY2ggaXMgd2hlbiBob21vbG9nb3VzIHBhaXJzIHNlcGFyYXRlLg==[Qq]

[c]IEVudGVyIHdvcmQ=[Qq]

[f]IE5vLCB0aGF0JiM4MjE3O3Mgbm90IGNvcnJlY3Qu[Qq]

[c]ICo=[Qq]

[f]IE5vLiBNZWlvc2lzIEkgaGFzIHR3byBrZXkgZmVhdHVyZXM6IGl0IHNlcGFyYXRlcyBob21vbG9nb3VzIHBhaXJzLCBhbmQgdGhlIGNocm9tb3NvbWVzIHRoYXQgYXJlIHNlcGFyYXRlZCBhcmUgY29tcG9zZWQgb2Ygc2lzdGVyIGNocm9tYXRpZHMgKHNvIHRoZXkmIzgyMTc7cmUgZG91YmxlZCku[Qq]

[q] The non-separation of either homologous pairs or of sister chromatids that can happen during meiosis is called [hangman]

[c]IG5vbmRpc2p1bmN0aW9u[Qq]

[f]IEV4Y2VsbGVudCE=[Qq]

[q] During Meiosis II, sister [hangman] are supposed to be separated.

[c]IGNocm9tYXRpZHM=[Qq]

[f]IEdvb2Qh[Qq]

[q]When an organism has a missing chromosome (instead of a homologous pair) it’s called a [hangman].

[c]bW9ub3NvbXk=[Qq]

[f]IEdyZWF0IQ==[Qq]

[q] When an organism has three chromosomes (instead of a homologous pair) it’s called a [hangman].

[c]IHRyaXNvbXk=[Qq]

[f]IEdyZWF0IQ==[Qq]

[/qwiz]

4. Nondisjunction, Down Syndrome, and other chromosomal variations.

We established above that

  • 95% of children with Down Syndrome have an extra 21st chromosome.
  • Incidence of Down Syndrome increases with maternal age, from 1 in 2000 births in 20-year-old mothers, to 1 in 30 births in 45-year-old mothers.

What’s the connection? Let me start by saying that the explanation that follows is still being developed. But the thinking is like this.

  1. A woman’s germ cells (the cells that produce her eggs) are formed when she’s an embryo.
  2. During embryonic development, a woman’s germ cells begin the process of meiosis and then pause in the middle of the process (after the DNA doubling that precedes Meiosis I, but before the separation of homologous pairs during Meiosis I or sister chromatids during Meiosis II).
  3. The chromosome separations and cell divisions that characterize meiosis resume during a woman’s ovulatory cycle. In other words, a 25-year-old woman is creating haploid eggs from a germ cell that’s been paused for 25 years. A 45-year-old woman is creating haploid eggs from a germ cell that’s been paused for 45 years.

The longer these cells have been paused, the longer the “junction” between homologous pairs or sister chromatids. That pause seems to increase the chance of nondisjunction, with resulting monosomies or trisomies.

In addition to Down Syndrome, there are a few other monosomies or trisomies that you should be familiar with.

  1. Trisomy 18: this causes significant developmental problems (much more severe than those associated with Down syndrome). Read more about it here.
  2. Turner Syndrome: This is monosomy of the X chromosome (sometimes annotated as “XO” to indicate that women with this condition have a single X chromosome, as opposed to two). Read more about it here.
  3. Klinefelter Syndrome: This is also called XXY syndrome. Individuals with Klinefelter are male but have an extra X chromosome. Read more about Klinefelter syndrome here.
  4. XYY Syndrome. Men with XYY have an extra Y chromosome in every cell of their bodies. Read more about XYY here.

5. Quiz: Sex determination, Nondisjunction, and Chromosomal Variation

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Sex determination, Nondisjunction, Chromosomal Variation (v2.0)”]

[h]Quiz: Nondisjunction and its consequences
[i]

[q] In the diagram below, the name for what’s happening at the blue arrow is

[c]IHN5bmFwc2lz[Qq]
[c]IGNyb3NzaW5nIG92ZXI=[Qq]
[c]IG5vbi1zZXBhcmF0aW9u[Qq]
[c]IG5vbmRpc2 p1bmN0aW9u[Qq]
[f]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[Qq]
[f]IE5vLiBDcm9zc2luZyBvdmVyIGlzIHdoZW4gaG9tb2xvZ291cyBjaHJvbW9zb21lcyBleGNoYW5nZSBwaWVjZXMgb2YgRE5BLCBjcmVhdGluZyBuZXcsIHJlY29tYmluYW50IGNocm9tb3NvbWVzIGluIHRoZSBnYW1ldGVzLiBUaGF04oCZcyBub3QgdmlzaWJsZSBoZXJlLiBXaGF0IHlvdSBjYW4gc2VlIGlzIHRoYXQgdGhlIHNpc3RlciBjaHJvbWF0aWRzIGZhaWxlZCB0byBzZXBhcmF0ZSwgYW5kIGJvdGggd2VudCB0byBvbmUgb2YgdGhlIGRhdWdodGVyIGNlbGxzIChsZWF2aW5nIHRoZSBvdGhlciBkYXVnaHRlciBjZWxsIHdpdGhvdXQgYW55IGNocm9tb3NvbWVzKS4gTG9vayBvdmVyIHRoZSBjaG9pY2VzLCBhbmQgc2VlIGlmIHlvdSBjYW4gZmluZCBhIG5hbWUgZm9yIHRoaXMgcHJvY2Vzcw==[Qq]
[f]IE5vLiBZb3UgY2hvc2UgYSB2ZXJ5IGxvZ2ljYWwgbmFtZSBmb3Igd2hhdCB5b3XigJlyZSBvYnNlcnZpbmcgKGFuZCB5b3UgbWlnaHQgaGF2ZSBiZWVuIG1pc2xlZCBieSB0aGUgaGludHMgZm9yIHRoZSBmaXJzdCB0d28gY2hvaWNlcyBhYm92ZS4gVGhlcmXigJlzIGEgbW9yZSBmb3JtYWwgbmFtZSBmb3IgdGhpcyBub24tc2VwYXJhdGlvbiBwcm9jZXNzLiBMb29rIGNhcmVmdWxseSBhdCB0aGUgY2hvaWNlcywgYW5kIHNlZSBpZiB5b3UgY2FuIGZpZ3VyZSBpdCBvdXQgbmV4dCB0aW1lLg==[Qq]
[f]IFllcy4gV2hhdCB5b3UgY2FuIHNlZSBpcyB0aGF0IHRoZSBzaXN0ZXIgY2hyb21hdGlkcyBmYWlsZWQgdG8gc2VwYXJhdGUsIGFuZCBib3RoIHdlbnQgdG8gb25lIG9mIHRoZSBkYXVnaHRlciBjZWxscyAobGVhdmluZyB0aGUgb3RoZXIgZGF1Z2h0ZXIgY2VsbCB3aXRob3V0IGFueSBjaHJvbW9zb21lcykuIFRoZSBuYW1lIGZvciB0aGlzIGVycm9yIGlzIG5vbi1kaXNqdW5jdGlvbi4=[Qq]

[q] In the diagram below, which of the numbered daughter cells has a trisomy?

[c]IDE=[Qq]
[c]IDI=[Qq]
[c]ID M=[Qq]
[c]IDQ=[Qq]
[f]IE5vLiBBIHRyaXNvbXkgbWVhbnMgMyBjaHJvbW9zb21lcywgaW5zdGVhZCBvZiBhIGhvbW9sb2dvdXMgcGFpci4gVGhpcyBmaXJzdCBjZWxsIGhhcyBhIGhvbW9sb2dvdXMgcGFpciAodHdvIHNpbmdsZSBjaHJvbW9zb21lcykuIE9uZSBtZW1iZXIgb2YgdGhlIHBhaXIgY2FtZSBmcm9tIHRoZSBzcGVybSwgYW5kIG9uZSBmcm9tIHRoZSBlZ2cuIE5leHQgdGltZSwgbG9vayBmb3IgYSBmZXJ0aWxpemVkIGVnZyAodGhlc2UgYXJlIGFsbCBvbiB0aGUgYm90dG9tIHJvdykgdGhhdCBoYXMgdGhyZWUgY2hyb21vc29tZXMsIGluc3RlYWQgb2YgYSBob21vbG9nb3VzIHBhaXIu[Qq]
[f]IE5vLiBBIHRyaXNvbXkgbWVhbnMgMyBjaHJvbW9zb21lcywgaW5zdGVhZCBvZiBhIGhvbW9sb2dvdXMgcGFpci4gVGhpcyBzZWNvbmQgY2VsbCBoYXMgYSBob21vbG9nb3VzIHBhaXIgKHR3byBzaW5nbGUgY2hyb21vc29tZXMpLiBPbmUgbWVtYmVyIG9mIHRoZSBwYWlyIGNhbWUgZnJvbSB0aGUgc3Blcm0sIGFuZCBvbmUgZnJvbSB0aGUgZWdnLiBOZXh0IHRpbWUsIGxvb2sgZm9yIGEgZmVydGlsaXplZCBlZ2cgKHRoZXNlIGFyZSBhbGwgb24gdGhlIGJvdHRvbSByb3cpIHRoYXQgaGFzIHRocmVlIGNocm9tb3NvbWVzLCBpbnN0ZWFkIG9mIGEgaG9tb2xvZ291cyBwYWlyLg==[Qq]
[f]IEV4Y2VsbGVudC4gQSB0cmlzb215IG1lYW5zIHRocmVlIGNocm9tb3NvbWVzLCBpbnN0ZWFkIG9mIGEgaG9tb2xvZ291cyBwYWlyLiBUaGF04oCZcyBleGFjdGx5IHdoYXQgeW91IHNlZSBpbiBjZWxsIG51bWJlciAzLg==[Qq]
[f]IE5vLiBBIHRyaXNvbXkgbWVhbnMgMyBjaHJvbW9zb21lcywgaW5zdGVhZCBvZiBhIGhvbW9sb2dvdXMgcGFpci4gVGhpcyBmb3VydGggY2VsbCBoYXMgYSBzaW5nbGUgY2hyb21vc29tZSwgaW5zdGVhZCBvZiBhIHBhaXIsIGEgY29uZGl0aW9uIGNhbGxlZCBhIOKAmG1vbm9zb215LuKAmSBOZXh0IHRpbWUsIGxvb2sgZm9yIGEgZmVydGlsaXplZCBlZ2cgKHRoZXNlIGFyZSBhbGwgb24gdGhlIGJvdHRvbSByb3cpIHRoYXQgaGFzIHRocmVlIGNocm9tb3NvbWVzLCBpbnN0ZWFkIG9mIGEgaG9tb2xvZ291cyBwYWlyLg==[Qq]

[q] In the diagram below, which of the numbered daughter cells has a monosomy?

[c]IDE=[Qq]
[c]IDI=[Qq]
[c]IDM=[Qq]
[c]ID Q=[Qq]
[f]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[Qq]
[f]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[Qq]
[f]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[Qq]
[f]IEV4Y2VsbGVudC4gTW9ub3NvbXkgbWVhbnMgb25lIGNocm9tb3NvbWUsIGluc3RlYWQgb2YgYSBob21vbG9nb3VzIHBhaXIsIHdoaWNoIGlzIGV4YWN0bHkgd2hhdCB5b3Ugc2VlIGluIGNlbGwgbnVtYmVyIGZvdXIu[Qq]

[q] The image below is a karyotype for

[c]IGEgY2hyb21vc29tYWxs eSBub3JtYWwgbWFsZQ==[Qq]
[c]IGEgY2hyb21vc29tYWxseSBub3JtYWwgZmVtYWxl[Qq]
[f]IFllcy4gTG9vayBhdCB0aGUgbGFzdCBwYWlyIG9mIGNocm9tb3NvbWVzLCBhbmQgbm90ZSB0aGF0IG9uZSBpcyBsYXJnZSwgdGhlIG90aGVyIGlzIHNtYWxsLiBUaGVzZSBhcmUgdGhlIHNleCBjaHJvbW9zb21lcyBvZiBhIG1hbGUgKFggYW5kIFkp[Qq]
[f]IE5vLiBBcyB5b3UgY2FuIHNlZSBieSB0aGUgbGFzdCBwYWlyIG9mIGNocm9tb3NvbWVzLCB0aGlzIHBlcnNvbiBoYXMgYW4gWCBhbmQgYSBZIGNocm9tb3NvbWUgKG9uZSBsYXJnZSwgb25lIHNtYWxsKS4gQSBmZW1hbGUgd291bGQgaGF2ZSB0d28gZXF1YWxseSBzaXplZCBjaHJvbW9zb21lcy4=[Qq]

[q] The image below is a karyotype for

[c]IGEgY2hyb21vc29tYWxseSBub3JtYWwgbWFsZQ==[Qq]
[c]IGEgY2hyb21vc29tYWxs eSBub3JtYWwgZmVtYWxl[Qq]
[f]IE5vLiBMb29rIGF0IHRoZSBsYXN0IHBhaXIgb2YgY2hyb21vc29tZXMsIGFuZCBub3RlIHRoYXQgb25lIGlzIGxhcmdlLCB0aGUgb3RoZXIgaXMgc21hbGwuIFRoZXNlIGFyZSB0aGUgc2V4IGNocm9tb3NvbWVzIG9mIGEgbWFsZSAoWCBhbmQgWSk=[Qq]
[f]IFllcy4gQXMgeW91IGNhbiBzZWUgYnkgdGhlIGxhc3QgcGFpciBvZiBjaHJvbW9zb21lcywgdGhpcyBwZXJzb24gaGFzIHR3byDigJhY4oCZIGNocm9tb3NvbWVzLCBtYWtpbmcgaGVyIGZlbWFsZS4=[Qq]

[q] Which of the following statements about sex chromosomes and gametes is true?
[c]IE1hbGVzIHBhc3Mgb24gYSDigJhZ4oCZIGNocm9tb3NvbWUgaW4gdGhlaXIgZ2FtZXRlcy4gRmVtYWxlcyBwYXNzIG9uIGFuIOKAmFjigJkgY2hyb21vc29tZS4=[Qq]
[c]IGJvdGggbWFsZXMgYW5kIGZlbWFsZXMgY2FuIGNyZWF0ZSBnYW1ldGVzIHRoYXQgY2FycnkgYSDigJhZ4oCZIGNocm9tb3NvbWUgb3IgYW4g4oCYWOKAmSBjaHJvbW9zb21lLg==[Qq]
[c]IFdoZW4gYSBtYW4gcHJvZHVjZXMgZ2FtZXRlcywgaGFsZiBvZiBoaXMgc3Blcm0gd2lsbCBjYXJyeSBhbiDigJhY4oCZIGNocm9tb3NvbWUsIGFuZCBoYWxmIG9mIGhpcyBzcG VybSB3aWxsIGNhcnJ5IGEg4oCYWeKAmSBjaHJvbW9zb21lLiBCeSBjb250cmFzdCwgYWxsIG9mIGEgd29tYW7igJlzIGVnZ3Mgd2lsbCBjYXJyeSBhbiBYIGNocm9tb3NvbWUu[Qq]
[f]IE5vLiBBIG1hbuKAmXMgc2V4IGNocm9tb3NvbWVzIGFyZSDigJhYWSzigJkgRHVyaW5nIG1laW9zaXMsIHRoZSBYIGFuZCBZIGNocm9tb3NvbWVzLCB3aGljaCBhcmUgaG9tb2xvZ291cywgd2lsbCBzZXBhcmF0ZS4gVGhlIHJlc3VsdGluZyBnYW1ldGVzIHdpbGwgZWl0aGVyIGhhdmUgYW4gWCBjaHJvbW9zb21lLCBvciBhIFkgY2hyb21vc29tZS4gWW91IGFyZSwgaG93ZXZlciwgcmlnaHQgYWJvdXQgdGhlIGZlbWFsZTogYSBmZW1hbGXigJlzIHNleCBjaHJvbW9zb21lcyBhcmUg4oCYWFgu4oCZIEFzIGEgcmVzdWx0LCBhbGwgb2YgdGhlIGVnZ3MgdGhhdCBzaGUgcHJvZHVjZXMgd2lsbCBoYXZlIGFuIFggY2hyb21vc29tZS4=[Qq]
[f]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[Qq]
[f]IFRoYXTigJlzIHJpZ2h0LiBBIG1hbuKAmXMgc2V4IGNocm9tb3NvbWVzIGFyZSDigJhYWSzigJkgRHVyaW5nIG1laW9zaXMsIHRoZSBYIGFuZCBZIGNocm9tb3NvbWVzLCB3aGljaCBhcmUgaG9tb2xvZ291cywgd2lsbCBzZXBhcmF0ZS4gVGhlIHJlc3VsdGluZyBnYW1ldGVzIHdpbGwgZWl0aGVyIGhhdmUgYW4gWCBjaHJvbW9zb21lLCBvciBhIFkgY2hyb21vc29tZS4gQSBmZW1hbGXigJlzIHNleCBjaHJvbW9zb21lcyBhcmUg4oCYWFgu4oCZIEFzIGEgcmVzdWx0LCBhbGwgb2YgdGhlIGVnZ3MgdGhhdCBzaGUgcHJvZHVjZXMgd2lsbCBoYXZlIGFuIFggY2hyb21vc29tZS4=[Qq]

[q] Which of the following statements about sex determination in humans is true?
[c]IFRoZSBlZ2cgZGV0ZXJtaW5lcyB0aGUgc2V4IG9mIGEgZmVtYWxlLiBUaGUgc3Blcm0gZGV0ZXJtaW5lcyB0aGUgc2V4IG9mIGEgbWFsZS4=[Qq]
[c]IFRoZSBzcGVybSBkZXRlcm1pbmVzIHRo ZSBzZXggb2YgdGhlIG9mZnNwcmluZy4=[Qq]
[c]IFRoZSBlZ2cgZGV0ZXJtaW5lcyB0aGUgc2V4IG9mIHRoZSBvZmZzcHJpbmcu[Qq]
[f]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[Qq]
[f]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[Qq]
[f]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[Qq]

[q] The image below shows the sex chromosomes of male and female fruit flies. Based on the diagram, you can infer that in fruit flies


[c]IFRoZSBlZ2cgZGV0ZXJtaW5lcyB0aGUgc2V4IG9mIGEgZmVtYWxlLiBUaGUgc3Blcm0gZGV0ZXJtaW5lcyB0aGUgc2V4IG9mIGEgbWFsZS4=[Qq]
[c]IFRoZSBzcGVybSBkZXRlcm1pbmVzIHRo ZSBzZXggb2YgdGhlIG9mZnNwcmluZy4=[Qq]
[c]IFRoZSBlZ2cgZGV0ZXJtaW5lcyB0aGUgc2V4IG9mIHRoZSBvZmZzcHJpbmcu[Qq]
[f]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[Qq]
[f]IENvcnJlY3QuIEl0JiM4MjE3O3MgZXhhY3RseSBsaWtlIGh1bWFucy4gQSBtYWxlJiM4MjE3O3Mgc2V4IGNocm9tb3NvbWVzIGFyZSBYWS7CoCBEdXJpbmcgbWVpb3NpcywgdGhlIFggYW5kIFkgY2hyb21vc29tZXMsIHdoaWNoIGFyZSBob21vbG9nb3VzLCB3aWxsIHNlcGFyYXRlLiBUaGUgcmVzdWx0aW5nIGdhbWV0ZXMgd2lsbCBlaXRoZXIgaGF2ZSBhbiBYIGNocm9tb3NvbWUgb3IgYSBZIGNocm9tb3NvbWUuIEEgZmVtYWxl4oCZcyBzZXggY2hyb21vc29tZXMgYXJlIFhYLiBBcyBhIHJlc3VsdCwgYWxsIG9mIHRoZSBlZ2dzIHRoYXQgc2hlIHByb2R1Y2VzIHdpbGwgaGF2ZSBhbiBYIGNocm9tb3NvbWUuIElmIGFuIFgtY2Fycnlpbmcgc3Blcm0gZmVydGlsaXplcyBhbiBlZ2csIHRoZSBvZmZzcHJpbmcgd2lsbCBiZSBYWCAoZmVtYWxlKS4gSWYgYSBZLWNhcnJ5aW5nIHNwZXJtIGZlcnRpbGl6ZXMgYW4gZWdnLCB0aGUgb2Zmc3ByaW5nIHdpbGwgYmUgWFkgKG1hbGUpLiBUaHVzLCB0aGUgc3Blcm0gZGV0ZXJtaW5lcyB0aGUgc2V4IG9mIHRoZSBvZmZzcHJpbmcu[Qq]
[f]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[Qq]

[q] What’s the best diagnosis of the karyotype below?

[c]IEEgY2hyb21vc29tYWxseSBub3JtYWwgbWFsZQ==[Qq]
[c]IFR1cm5lciBT eW5kcm9tZQ==[Qq]
[c]IEtsaW5mZWx0ZXIgU3luZHJvbWU=[Qq]
[c]IERvd24gU3luZHJvbWU=[Qq]
[f]IE5vLiBMb29rIGF0IHRoZSBzZXggY2hyb21vc29tZXMuIEEgY2hyb21vc29tYWxseSBub3JtYWwgbWFsZSB3b3VsZCBoYXZlIGFuIFggYW5kIGEgWSBjaHJvbW9zb21lLiBOZXh0IHRpbWUsIGNob29zZSBhIGRpZmZlcmVudCBhbnN3ZXIu[Qq]
[f]IFllcy4gQXMgeW91IGNhbiBzZWUsIHRoaXMgZmVtYWxlIGhhcyBhIHNpbmdsZSBYIGNocm9tb3NvbWUsIHdoaWNoIGlzIHRoZSBjaHJvbW9zb21hbCBjYXVzZSBvZiBUdXJuZXIgc3luZHJvbWUu[Qq]
[f]IE5vLiBMb29rIGF0IHRoZSBzZXggY2hyb21vc29tZXMuIFlvdSBjYW4gc2VlIHRoYXQgdGhlcmXigJlzIGEgc2luZ2xlIFggY2hyb21vc29tZS4gS2xpbmVmZWx0ZXIgaXMgYSBzeW5kcm9tZSB0aGF0IGltcGFjdHMgbWFsZXMsIGFuZCBpdOKAmXMgY2F1c2VkIGJ5IGFuIGV4dHJhIFggY2hyb21vc29tZSAoYXMgb3Bwb3NlZCB0byBhIG1pc3NpbmcgWCBjaHJvbW9zb21lLCB3aGljaCBpcyB3aGF0IHlvdSBzZWUgaGVyZS4=[Qq]
[f]IE5vLiBEb3duIHN5bmRyb21lIGlzIGNhdXNlZCBieSBhbiBleHRyYSAyMXN0IGNocm9tb3NvbWUgKHRyaXNvbXkgMjEpLiBUaGlzIHBlcnNvbiBvbmx5IGhhcyB0d28gMjFzdCBjaHJvbW9zb21lcy4=[Qq]

[q] What’s the best diagnosis of the karyotype below?

[c]IEEgY2hyb21vc29tYWxseSBub3JtYWwgbWFsZQ==[Qq]
[c]IFR1cm5lciBTeW5kcm9tZQ==[Qq]
[c]IEtsaW5mZWx0ZX IgU3luZHJvbWU=[Qq]
[c]IERvd24gU3luZHJvbWUu[Qq]
[f]IE5vLiBMb29rIGF0IHRoZSBzZXggY2hyb21vc29tZXMuIFRoZXJlIGFyZSB0d28gWCBjaHJvbW9zb21lcyBhbmQgYSBZIGNocm9tb3NvbWUuIEEgY2hyb21vc29tYWxseSBub3JtYWwgbWFsZSB3b3VsZCBoYXZlIGp1c3Qgb25lIFggY2hyb21vc29tZSBhbmQgb25lIFkgY2hyb21vc29tZS4gTmV4dCB0aW1lLCBjaG9vc2UgYSBkaWZmZXJlbnQgYW5zd2VyLg==[Qq]
[f]IE5vLiBMb29rIGF0IHRoZSBzZXggY2hyb21vc29tZXMuIFRoZXJlIGFyZSB0d28gWCBjaHJvbW9zb21lcyBhbmQgYSBZIGNocm9tb3NvbWUuIEEgcGVyc29uIHdpdGggVHVybmVyIHN5bmRyb21lIGhhcyBhIHNpbmdsZSBYIGNocm9tb3NvbWUgKFhPKS4gTmV4dCB0aW1lLCBjaG9vc2UgYSBkaWZmZXJlbnQgYW5zd2VyLg==[Qq]
[f]IEV4YWN0bHkuIExvb2sgYXQgdGhlIHNleCBjaHJvbW9zb21lcy4gVGhlcmUgYXJlIHR3byBYIGNocm9tb3NvbWVzIGFuZCBhIFkgY2hyb21vc29tZS4gVGhpcyBpcyB0aGUgY2hyb21vc29tYWwgY2F1c2Ugb2YgS2xpbmVmZWx0ZXIgc3luZHJvbWUgKFhYWSku[Qq]
[f]IE5vLiBEb3duIHN5bmRyb21lIGlzIGNhdXNlZCBieSBhbiBleHRyYSAyMXN0IGNocm9tb3NvbWUgKHRyaXNvbXkgMjEpLiBUaGlzIHBlcnNvbiBvbmx5IGhhcyB0d28gMjFzdCBjaHJvbW9zb21lcy4=[Qq]

[q] What’s the best diagnosis of the karyotype below?

[c]IERvd24gU3 luZHJvbWUu[Qq]
[c]IFR1cm5lciBTeW5kcm9tZQ==[Qq]
[c]IEtsaW5mZWx0ZXIgU3luZHJvbWU=[Qq]
[f]IFllcy4gRG93biBzeW5kcm9tZSBpcyBjYXVzZWQgYnkgYW4gZXh0cmEgMjFzdCBjaHJvbW9zb21lICh0cmlzb215IDIxKS4=[Qq]
[f]IE5vLiBBIHBlcnNvbiB3aXRoIFR1cm5lciBzeW5kcm9tZSBoYXMgYSBzaW5nbGUgWCBjaHJvbW9zb21lIChYTykuIEluIHRlcm1zIG9mIHRoZSBzZXggY2hyb21vc29tZXMsIHRoaXMgcGVyc29uIGlzIGEgbm9ybWFsIG1hbGUsIHdpdGggYW4gWCBhbmQgYSBZIGNocm9tb3NvbWUuIFRoZSB0aGluZyB0byBsb29rIGZvciBoZXJlIGlzIHRoZSAyMXN0IGNocm9tb3NvbWUuIFRha2UgYSBsb29rLCBhbmQgY2hvb3NlIGEgZGlmZmVyZW50IGFuc3dlciBuZXh0IHRpbWUu[Qq]
[f]IE5vLiBBIG1hbiB3aXRoIEtsaW5lZmVsdGVyIHN5bmRyb21lIGhhcyB0d28gWCBjaHJvbW9zb21lcywgYW5kIGEgWSBjaHJvbW9zb21lIChYWFkpLiBJbiB0ZXJtcyBvZiB0aGUgc2V4IGNocm9tb3NvbWVzLCB0aGlzIHBlcnNvbiBpcyBhIG5vcm1hbCBtYWxlLCB3aXRoIGFuIFggYW5kIGEgWSBjaHJvbW9zb21lLiBUaGUgdGhpbmcgdG8gbG9vayBmb3IgaGVyZSBpcyB0aGUgMjFzdCBjaHJvbW9zb21lLiBUYWtlIGEgbG9vaywgYW5kIGNob29zZSBhIGRpZmZlcmVudCBhbnN3ZXIgbmV4dCB0aW1lLg==[Qq]

[q] The chromosomal pattern associated with Turner syndrome is
[c]IFRyaXNvbXkgMjE=[Qq]
[c]IFhYWQ==[Qq]
[c]IF hP[Qq]
[c]IFhZWQ==[Qq]
[f]IE5vLiBUcmlzb215IDIxIGlzIGFzc29jaWF0ZWQgd2l0aCBEb3duIFN5bmRyb21lLiBUdXJuZXIgc3luZHJvbWUgaXMgZm91bmQgb25seSBpbiBmZW1hbGVzIGFuZCBpbnZvbHZlcyBpbmhlcml0aW5nIGEgc2luZ2xlIFggY2hyb21vc29tZS4gVXNlIHRoYXQgaW5mb3JtYXRpb24gdG8gY2hvb3NlIGEgZGlmZmVyZW50IGFuc3dlciBuZXh0IHRpbWUu[Qq]
[f]IE5vLiBYWFkgaXMgYXNzb2NpYXRlZCB3aXRoIEtsaW5lZmVsdGVyIHN5bmRyb21lLiBUdXJuZXIgc3luZHJvbWUgaXMgZm91bmQgb25seSBpbiBmZW1hbGVzIGFuZCBpbnZvbHZlcyBpbmhlcml0aW5nIGEgc2luZ2xlIFggY2hyb21vc29tZS4gVXNlIHRoYXQgaW5mb3JtYXRpb24gdG8gY2hvb3NlIGEgZGlmZmVyZW50IGFuc3dlciBuZXh0IHRpbWUu[Qq]
[f]IFllcy4gVHVybmVyIHN5bmRyb21lIGlzIGNhdXNlZCBieSB0aGUgaW5oZXJpdGFuY2Ugb2YgYSBzaW5nbGUgWCBjaHJvbW9zb21lLCByZXByZXNlbnRlZCBieSB0aGUgbm90YXRpb24gWE8u[Qq]
[f]IE5vLiBYWVkgaXMgY2F1c2VkIGJ5IHRoZSBpbmhlcml0YW5jZSBvZiBhbiBleHRyYSBZIGNocm9tb3NvbWUuIFR1cm5lciBzeW5kcm9tZSBpcyBmb3VuZCBvbmx5IGluIGZlbWFsZXMgYW5kIGludm9sdmVzIGluaGVyaXRpbmcgYSBzaW5nbGUgWCBjaHJvbW9zb21lLiBVc2UgdGhhdCBpbmZvcm1hdGlvbiB0byBjaG9vc2UgYSBkaWZmZXJlbnQgYW5zd2VyIG5leHQgdGltZS4=[Qq]

[q] The chromosomal pattern associated with Klinefelter syndrome is
[c]IFRyaXNvbXkgMjE=[Qq]
[c]IFhY WQ==[Qq]
[c]IFhP[Qq]
[c]IFhZWQ==[Qq]
[f]IE5vLiBUcmlzb215IDIxIGlzIGFzc29jaWF0ZWQgd2l0aCBEb3duIFN5bmRyb21lLiBLbGluZWZlbHRlciBzeW5kcm9tZSBvY2N1cnMgaW4gbWFsZXMgd2hvIGluaGVyaXQgYW4gZXh0cmEgWCBjaHJvbW9zb21lLiBVc2UgdGhhdCBpbmZvcm1hdGlvbiB0byBjaG9vc2UgYSBkaWZmZXJlbnQgYW5zd2VyIG5leHQgdGltZS4=[Qq]
[f]IFllcy4gWFhZIGlzIGFzc29jaWF0ZWQgd2l0aCBLbGluZWZlbHRlciBzeW5kcm9tZS4gS2xpbmVmZWx0ZXIgc3luZHJvbWUgb2NjdXJzIGluIG1hbGVzIHdobyBpbmhlcml0IGFuIGV4dHJhIFggY2hyb21vc29tZS4=[Qq]
[f]IE5vLiBUdXJuZXIgc3luZHJvbWUgaXMgY2F1c2VkIGJ5IHRoZSBpbmhlcml0YW5jZSBvZiBhIHNpbmdsZSBYIGNocm9tb3NvbWUsIHJlcHJlc2VudGVkIGJ5IHRoZSBub3RhdGlvbiBYTy4gS2xpbmVmZWx0ZXIgc3luZHJvbWUgb2NjdXJzIGluIG1hbGVzIHdobyBpbmhlcml0IGFuIGV4dHJhIFggY2hyb21vc29tZS4gVXNlIHRoYXQgaW5mb3JtYXRpb24gdG8gY2hvb3NlIGEgZGlmZmVyZW50IGFuc3dlciBuZXh0IHRpbWUu[Qq]
[f]IE5vLiBYWVkgaXMgY2F1c2VkIGJ5IHRoZSBpbmhlcml0YW5jZSBvZiBhbiBleHRyYSBZIGNocm9tb3NvbWUuIEtsaW5lZmVsdGVyIHN5bmRyb21lIG9jY3VycyBpbiBtYWxlcyB3aG8gaW5oZXJpdCBhbiBleHRyYSBYIGNocm9tb3NvbWUuIFVzZSB0aGF0IGluZm9ybWF0aW9uIHRvIGNob29zZSBhIGRpZmZlcmVudCBhbnN3ZXIgbmV4dCB0aW1lLg==[Qq]

[q] The chromosomal pattern associated with Down syndrome is
[c]IFRyaXNv bXkgMjE=[Qq]
[c]IFhYWQ==[Qq]
[c]IFhP[Qq]
[c]IFhZWQ==[Qq]
[f]IFllcy4gVHJpc29teSAyMSBpcyBhc3NvY2lhdGVkIHdpdGggRG93biBTeW5kcm9tZS4gVHJpc29teSAyMSBpcyBhbm90aGVyIHdheSBvZiBzYXlpbmcgdGhhdCB0aGVyZSBhcmUgdGhyZWUgY2hyb21vc29tZXMsIGluc3RlYWQgb2YgdHdvIChhIGhvbW9sb2dvdXMgcGFpciku[Qq]
[f]IE5vLiBYWFkgaXMgYXNzb2NpYXRlZCB3aXRoIEtsaW5lZmVsdGVyIHN5bmRyb21lLiBEb3duIHN5bmRyb21lIGlzIGNhdXNlZCBieSBhbiBleHRyYSBjaHJvbW9zb21lLCBidXQgbm90IGluIHRoZSBzZXggY2hyb21vc29tZXMuIFNlZSBpZiB5b3UgY2FuIGZpbmQgdGhhdCBleHRyYSBjaHJvbW9zb21lIGluIHRoaXMgaW1hZ2Ugd2hlbiB5b3Ugc2VlIHRoaXMgcXVlc3Rpb24gYWdhaW4u[Qq]
[f]IE5vLiBYTyBpcyBhc3NvY2lhdGVkIHdpdGggVHVybmVyIHN5bmRyb21lLCBhbmQgaXQgaW52b2x2ZXMgYSBtaXNzaW5nIFggY2hyb21vc29tZS4gRG93biBzeW5kcm9tZSBpcyBjYXVzZWQgYnkgYW4gZXh0cmEgY2hyb21vc29tZSwgYnV0IG5vdCBpbiB0aGUgc2V4IGNocm9tb3NvbWVzLiBTZWUgaWYgeW91IGNhbiBmaW5kIHRoYXQgZXh0cmEgY2hyb21vc29tZSBpbiB0aGlzIGltYWdlIHdoZW4geW91IHNlZSB0aGlzIHF1ZXN0aW9uIGFnYWluLg==[Qq]
[f]IE5vLiBYWVkgaXMgY2F1c2VkIGJ5IHRoZSBpbmhlcml0YW5jZSBvZiBhbiBleHRyYSBZIGNocm9tb3NvbWUuIERvd24gc3luZHJvbWUgaXMgY2F1c2VkIGJ5IGFuIGV4dHJhIGNocm9tb3NvbWUsIGJ1dCBub3QgaW4gdGhlIHNleCBjaHJvbW9zb21lcy4gU2VlIGlmIHlvdSBjYW4gZmluZCB0aGF0IGV4dHJhIGNocm9tb3NvbWUgaW4gdGhpcyBpbWFnZSB3aGVuIHlvdSBzZWUgdGhpcyBxdWVzdGlvbiBhZ2Fpbi4=[Qq]
[x]
[restart]

[/qwiz]

6. What’s next?

To consolidate your understanding of Meiosis (and related issues like sex determination and non-disjunction) proceed to Topic 5.1, 5.2, 5.6: Meiosis, Sex Determination, and Nondisjunction Cumulative Flashcards and Multiple Choice Speed Trial