DNA BANDING

What is DNA Banding?A method used to identify multilocus DNA banding patterns that are specific to an individual

KaryotypesLooking at Chromosomes

Why?We can learn a lot by looking at chromosomes! They can tell us everything from the likelihood that an unborn baby will have a genetic disorder to whether a person will be male or female.

How?Scientists often analyze chromosomes in prenatal testing and in diagnosing specific diseases. Fetal cells from an unborn child are contained in the amniotic fluid and can be tested for hereditary disorders such as Tay-Sachs or Phenylketonuria.

DiscussionWould you want to know if your baby had a disease?

What would be the benefits?What would be the consequences?

Chromosome ReviewChromosomes are

compact spools of DNA. If you were to stretch out all the DNA from one of your cells, it would be over 3 feet (1 meter) long from end to end! You can think of chromosomes as "DNA packages" that enable all this DNA to fit in the nucleus of each cell.

HumansNormally, we have 46 chromosomes in each cell  23 from our mother and 23 from our father. 

What is a Karyotype?A karyotype is an organized profile of a person's chromosomes. In a karyotype, chromosomes are arranged and numbered by size, from largest to smallest. This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder.

How are Karyotypes Prepared?To make a karyotype, scientists take a

picture of someone's chromosomes, cut them out and match them up using size, banding pattern and centromere position as guides. Homologous pairs are arranged by size in descending order (largest to smallest) with the sex chromosomes (XX for female or XY for male) as the last or 23 pair.

Homologous chromosomes have genes for the same trait at the same location.

Since humans have 46 chromosomes in their somatic or body cells, they have 23 pairs of chromosomes in their karyotype.

A person may have more or less than the normal 46 chromosomes on their karyotype.

Nondisjunction is a condition that occurs if chromosomes fail to separate in meiosisExample: A disorder called Down Syndrome  A person with Down Syndrome will have 3

chromosomes in their 21st pair.

Normal Female

Normal Male

Down’s Syndrome

Turner’s Syndrome

Klinfelter Syndrome

Super Female

Cri Du Chat Syndrome

Karytype Practice

____ 1. A. Normal B. Abnormal____2. A. Male B. Female

Karyotype Practice

____3. A. Normal B. Abnormal____4. A. Male B. Female____5. A. Turner’s B. Klinefelter’s

C. Down’s D. Super female

Karyotype Practice

____6. A. Normal B. Abnormal____7. A. Male B. Female____8. A. Super female B. Turner’s

C. Down’s D. Klinefelter’s

Karyotype Practice

____ 9. A. Normal B. Abnormal____10. A. Male B. Female____11. A. Down’s B. Super female

C. Cri du chat D. Turner’s E. None of the above

Karyotype Practice

____12. A. Normal B. Abnormal____13. A. Down’s B. Klinefelter’s

C. Turner’s D. Normal____14. A. Male B. Female____15. The genotype is:

A. XXX B. XO C. XXY D. Normal

Karyotype Practice

____16. A. Normal B. Turner’s C. Klinefelter’s D. super female

E. Down’s____17. This karyotype shows a:

A. sex – chromosome disorder B. Autosomal disorder C. Normal karyotype

Karyotype Practice

18. A. Normal B. Abnormal19. A. Male B. Female