Karyotypes

A summary of karyotypes:

Here is a human karyotype showing all 46 chromosomes:

Note that the autosomes are all against a purple background and the two sex chromosomesare in the lower right hand corner and are labeled "X" and "Y"

XX = female
XY = male

This example is a male, because there is one X and one Y chromosome (XY).

The autosomes are arranged as 22 homologous pairs...one from each parent. Note that males do not have a homologous pair to the X sex chromosome or the Y sex chromosome.

Females have two X chromosomes, so they DO have homologous pairs for all of their chromosomes.

The chromosomes in that first picture are shown unduplicated. There are no sister chromosomes present, just the homologous pairs.

If there were sisters, each homologous pair would look like two Xs (not to be confused with the X chromosome...) like this picture:

So, in this picture, each "X" shape is a pair of attached sister chromatids and each numbered pair of "Xs" is a duplicated homologous pair.

Sister chromatids are identical copies (a result of DNA synthesis or replication) and are attached to their "sister" at the centromere.

Humans have a total of 46 chromosomes. This is called the diploid number because there are two of each kind of chromosome.

Gametes would have only one of each homologous pair, and would be called haploid.

**Note: haploid and diploid refer to the genome in its unduplicated state.

I don't have a picture of a gamete karyotype. Can you imagine what it would look like?

Some practice questions for the following karyotype (answers at the bottom):
Is this individual male or female?
How many chromosomes are there?
Is this normal for a human?
Are there sister chromatids in this picture?
Are there homologous pairs in this picture? If so, how many pairs?
Is this haploid or diploid?
Is there anything genetically wrong with this individual?
.
.
.
.
.
.


(Answers: male; 46; yes; no (there are no "Xs"); yes...22 pairs; diploid (haploid would be 23 chromosomes...a gamete); yes--trisomy 21 or Down's Syndrome)

DNA Synthesis and Protein Synthesis Animations

Here's a web page another student recommended. It has a nice animation on DNA synthesis AND protein synthesis:

STUMBLE LINK

More DNA animations:

LINK 1 (realistic)

LINK 2 (cartoon)

Here's a nice animation of the replication fork (click the bottom link that says "DNA Replication Fork" on THIS PAGE)

Protein Synthesis Animations:
There are some good ones at this link: Animations
Here's another one from a classmate: LINK

Here are the two more little animations...I think they summarize transcription and translation nicely and might be a helpful review: