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
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:
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?
.
.
.
.
.
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(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)
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.
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)
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