Chromosomes and Karyotyping

1. Chromosomes and Karyotyping

2. What is a Chromosome? • http://gslc.genetics.utah.edu/units/basics/tour/ • Chromosome • unit for packaging DNA into the nucleus of cells • threadlike strand of DNA and proteins • DNA wrapped around proteins

3. Different levels of DNA condensation. (1) Single DNA strand. (2) Chromatin strand (DNA with histones). (3) Chromatin during interphase with centromere. (4) Condensed chromatin during prophase. (Two copies of the DNA molecule are now present) (5) Chromosome during metaphase. Histone – name of the proteins that DNA wrap around in the formation of chromosomes

4. Chromatid – one of two identical parts of chromosome Centromere – constricted area where the two chromatids are held together Be able to identify these as well as the short arm and the long arm of the chromosome Chromosome. (1) Chromatid. One of the two identical parts of the chromosome after S phase. (2) Centromere. The point where the two chromatids touch, and where the microtubules attach. (3) Short arm. (4) Long arm.

5. Human chromosomes • Humans have 46 total chromosomes in somatic (body) cells • Two sets in each cell: • One set from mother one set from father • 22 pairs plus the sex chromosomes (X and Y) • Reproductive cells (sperm and egg) contain one set of chromosomes

6. Meiosis • Process of cell division to create gametes • Gametes – sex cells, sperm or egg • Following meiosis, each gamete will normally have one copy of each chromosome for a total of 23

7. Fertilization • Egg and sperm fuse to form zygote • Zygote – fertilized egg • The zygote created will have two of each chromosome – one set from each parent

8. Making a Karyotype http://gslc.genetics.utah.edu/units/disorders/karyotype/karyotype.cfm

9. Chromosome pairs • Chromosomes numbered 1-22 plus x and/or Y • Paired based on size, location of centromeres, banding pattern after staining • Normal members of a particular species have the same number of chromosomes

10. Organisms of different species have different numbers of chromosomes Table 1: Examples of chromosome numbers (diploid). Species # of chromosomes Species # of chromosomes Fruit fly 8 Human 46 Rye 14 Ape 48 Guinea Pig 16 Sheep 54 Dove 16 Horse 64 snail 24 Chicken 78 Earthworm 36 Carp 104 Pig 40 Butterflies ~380 Wheat 42 Fern ~1200

11. Karyotype • Complete set of chromosomes in the cell • The karyotype of the human female contains 23 pairs of chromosomes: • 22 pairs of autosomes(chromosome NOT sex chromosome) • 1 pair of X chromosomes • The karyotype of the human male contains: • same 22 pairs of autosomes • one X chromosome • one Y chromosome

12. What to look for in a Karyotype • Are there 46 chromosomes? • Are there 2 identical pairs of each autosome? • Are there 2 sex chromosomes? • Are there any rearrangements between chromosomes or large deletions?

13. What happens when a person has something different? • Too many or too few chromosomes • Missing pieces of chromosomes • Mixed up pieces of chromosomes Chromosome Abnormalities

14. Too many or too few… • Abnormal meiosis – incorrect distribution of chromosomes into egg and sperm cells • abnormal meiosis • People who are born with an abnormal number of chromosomes often have genetic disorders

15. Missing pieces… • Deletions – when a piece of DNA is absent from a chromosome • Deletions • Large deletions result in the loss of many genes • This leads to genetic disorders

16. Mixed up pieces… • Translocation – chromosome rearrangement, piece breaks off, reattaches to another chromosome • Translocation • Once again, causes genetic disorders

17. Genetic disorders • condition caused by absent or defective gene or by chromosomal aberration

18. Down’s Syndrome (Trisomy 21) • Down Syndrome • Three copies of chromosome 21 • Mental retardation, eyes that slant upward, heart defects • 90% of time, extra chromosome comes from mother’s egg

19. Turner Syndrome (Monosomy) • Turner Syndrome • Single X chromosome • Short stature, lack of ovarian development • 75-80% of time, sperm lacks sex chromosome

20. Klinefelter Syndrome (Trisomy) • Klinefelter Syndrome • 2 X + Y chromosomes • Develop as males, tall, do not develop secondary sex characteristics (facial hair, etc) • 50% of time extra chromosome from father 50% of time from mother

21. Cri du chat syndrome • Cri du chat Syndrome • Deletion on short arm of chromosome 5 • “cry of the cat” French • Abnormal larynx development • Becomes normal ~ 3 weeks after birth • 80% chromosome with deletion from sperm

22. Williams Syndrome • williams syndrome • Deletion on long arm of chromosome 7, codes for elastin gene • Protein provides strength and stretchiness to blood vessels • Circulatory system disorders

23. Philadelphia Chromosome • reciprocal translocation • Most of chromosome 22 on long arm of chromosome 9 • Chronic myelogenous leukemia • Cells that produce blood cells grow uncontrollably

24. Robertsonian Translocation • Translocation • balance robertsonian – no genetic material lost • Problems in meiosis may occur • Can result in trisomy, monosomy, normal chromosomes, or carrier of translocation

25. Online Karyotype • interactive karyotyping • http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html • Assignment: complete paper karyotype