Karyotype and genetic disease

1. Karyotype and genetic disease

2. The numberof chromosome per species is fixed • Each species has a characteristic number of chromosomes which is constant for that species: Examples: • Human: 46 chromosomes • Mouse: 40 chromosomes • Onion: 16 chromosomes

3. The shapeof a chromosome is characteristic • Length • Position of the centromere (constriction that can occur anywhere along the chromosome, but always in the same position on a given chromosome) Size of the arms depends on the position of the centromere Centromere in the center Centromere close to the end

4. karyotype (picture of a person's chromosomes):

5. Karyotyping: Examination of the chromosomes: Number structure

6. To obtain a karyotype: Chromosomes are isolated, stained, and examined under the microscope. A picture of the chromosomes is taken through the microscope.  The picture of the chromosomes is cut up and chromosomes are arranged as homologous pairs in descending order of size.

7. Karyotype Chromosomes are numbered: each chromosome has been assigned a number based on its size; the largest chromosome is chromosome 1. The 23rd pair of chromosomes are sex chromosomes which determine the gender: Female: two X chromosomes Male: an X and a Y chromosome.  22 numbered pairs of human chromosomes, called autosomes (autosomal chromosomes)

8. Karyotyping • The test can be performed on almost any tissue, including: • Amniotic fluid * • Placenta (chorionic villus sampling) * • Blood • Bone marrow • *the genetic material in the amniotic fluid and chorionic villus cells is the same as that in the baby's cells.

9. Amniocentesis • Allows: • Pre-natal diagnosis of chromosome abnormalities • Gender determination

11. http://learn.genetics.utah.edu/content/chromosomes/karyotype/http://learn.genetics.utah.edu/content/chromosomes/karyotype/

12. Human abnormalities due to alterations in chromosome number A pair of homologues chromosomes may not separate during meiosis I or sister chromosomes fail to separate properly during meiosis II: Non-disjunction Result: formation of gametes with too many chromosomes or too few (aneuploid); Baby is born with genetic disease

13. Error in meiosis and genetic disease Nondisjunction of chromosome 21 during egg formation: Down syndrome(trisomy 21), individual has 3 copies of chromosome 21 (47 chromosomes) Mental retardation and distinct physical traits; Probability increases with age of the mother Under 20 years: risk about 1:1700 20-30 years: risk about 1:1400 30-35 years: risk about 1:750 45 years: risk about 1:16

14. Error in meiosis and genetic disease Loss of a chromosome is always lethal

15. Human abnormalities due to non-disjunction of sex chromosomes XX do not separate: resulting gametes: XX and O If an XX gamete combines with an X gamete, the resulting zygote is a female XXX, usually sterile (XXX Syndrome); If an XX gamete combines with a Y gamete, the resulting zygote is XXY, infertile male with enhanced female characteristics (breast) and diminished mental capacities (Klinefelter syndrome) If a O gamete combines with a Y gamete, the resulting zygote is nonviable If a O gamete combines with an X gamete, the resulting zygote is XO, sterile female, does not mature sexually (Turner syndrome)

16. Human abnormalities due to alterations in sex chromosome number Nondisjunction of XY chromosomes: YY gamete If a YY gamete combines with an X gamete, the resulting zygote is XYY, fertile male, with learning difficulties and violent tendencies