What are they?? How do we use them? Karyotypes What are they?? How do we use them?

Karyotypes – What are they? A karyotype is a photo of the chromosomes in a cell that shows the chromosomes arranged by size.

Karyotypes – What are they? A normal human karyotype should have 46 chromosomes. 23 pairs of homologous chromosomes The last pair (pair 23) determines if the human is male or female Also known as the sex chromosomes

Normal Karyotype--male A normal male karyotype has 1 X chromosome and 1 Y chromosome in the 23rd pair Male = XY

Normal Karyotype--female A normal female karyotype has 2 X chromosomes in the 23rd pair female = XX

Is this person female or male?

Karyotypes – How do we use them? Karyotypes can reveal genetic disorders by showing changes in chromosome number or large deletions in chromosomes

How are DNA samples obtained for karyotypes?

If there are chromosomal number abnormalities, how do they form? If there is a mistake when chromosomes are separating during meiosis, then the resulting sperm or egg will have too many or too few chromosomes. This is called Nondisjunction

Nondisjunction

So, what do you look for when examining a karyotype? Are there 46 chromosomes? Are there 2 identical pairs of each chromosome and 2 sex chromosomes? Are there any rearrangements between chromosomes or large deletions?

Trisomy 21 or Down Syndrome Caused by nondisjunction The #21 chromosomes ends up with 3 chromosomes instead of 2 Humans with Trisomy 21 have 47 chromosomes total

Correlation between mother’s age and Trisomy 21 incidence

Turners syndrome Caused by nondisjunction There is only 1 X chromosome and no Y chromosome Humans with Turners syndrome have 45 chromosomes total

Klinefelter syndrome Caused by nondisjunction There are 2 X chromosomes and 1 Y chromosome Humans with Klinefelter syndrome have 47 chromosomes total

Is this a normal karyotype?? Male or Female? Is this a normal karyotype?? XXY Male (Extra X)

What we can’t see Individual DNA strands or genes The number of genes in any given area of a chromosome. The presence or location of small mutations. (Scientists cannot predict diseases caused by small mutations within genes.

Other chromosomal disorders that can arise?

Problems with chromosomes Duplication: copied parts of chromosome A B C D A B C D

Problems with chromosomes Deletion: missing parts of chromosome A B C D A D

Deletion—18 Q Deletion Syndrome Caused by deletion Parts of the #18 chromosomes have been deleted

Problems with chromosomes Inversion: parts of chromosome flipped A B C D A C B D

Chromosomal mutations Deletion Duplication Inversion Translocation

Human genetic disorders Sometimes the alleles inherited contribute to disorders, or diseases, and not from the number or shape of the chromosomes. Types include: Sex-linked: genes found on X or Y chromosome Recessive: requires 2 allele copies to express disorder Dominant: requires only 1 allele copy to express disorder

Recessive disorders

Dominant disorder