-An inactive X chromosome in a female cell

-easily detected in a buccal swab

-Karyotypes are used because barr bodies are efficient 

- every extraneous x-chromosome is inactivated therefore females have an extra chromosome

- An X-heterozygote female is mosaic for expression of a trait

* meaning= 2 cells originating from the same        body: one can be active and the other inactive

1. take a blood sample

2. addition of phytohemagglutinin 

-initiate division of lymphocytes

3. Incubate @ normal temp for 3 days

4. addition of cholchichine

-arrest cells in metaphase

5. addition of hypolonic saline

6. cells are fixed

7. place a drop allowing spreading

8. Digest with trypsin and stain with giemsa

1. Blood (leukocytes) --> culture for 2-3 days

- most favored

2. Bone marrow biopsy --> no culture

- lease favored

- very painful

3. Fibroblast cells --> culture for 2-3 weeks

- not efficient

1. Amniotic cells (fluid around the fetus)

- culture for 2-4 wks

- procedure cant be done till 14-16 wks

2. Chorionic Villus (culture from placenta)

- no culture unless cells are separated from mother

- fast dividing have to wait till 13 wks

- (13-15): acrocentric

- (21-22): small acrocentric

- 3 copies of all chromosomes

- 3 copies = triploid

- early spontaneous abortions

- reason fro early pregnancy loss

- excess of one chromosome

- trisomy with 13, 18, 21, 22, and X or Y are compatible with life

- Trisomy 16 is most common but leads to a spontaneous aborption

- Trisomy 21 is the smallest chromosome

* 80% will die in utero or stillbirth

**note as you decrease in number is has a greater affect

- lack of one chromosome

- only monosomy X is compatible with life

(# of chrom)(sex type)(type of sturcture abnor)(chromosome involved)(breakpoints in abnor)

- A chromosome with 2 identical arms

- p and q arms are pulled apart instead of sister chromatids

- you have 2 copies of chromosome are there with missing parts

- looses the telomeres @ both ends and become a ring

- due to telomere dysfunction & double-strand breaks

- Exchange of centric & acentric fragments

- results

* dicentric + acentric chromosomes

* not stable in mitosis

- Exchange of 2 acentric fragments

* stable reciprocal translocation

* normal phenotype

- Exchange in proximal short arms (p arms)

*stable translocation

* 2 centromere fuse to create a monocentric chromosome

- a no named syndrome

- mental retardation and heart defects

Down syndrome

(trisomy 21)

- 40% have heart defects

- 80% dies as a fetus

*60% are spontaneous

*20% are stillborn

- 20% make it to life birth

Effects of a aging Down syndrome

patient

- Alheimers Disease

Effect of translocations 

on Down syndrome patients

1. robersonian 14-21 translocation

* 1 of the 2 copies of chromosome 21 is translocated to chromosome 14

* will live

2. ribersonian 21-21 translocation

*no live children born

- virilized ovaries

cause: exposure to progesterone or androgen

- deficiency 11(5%) & 21(95%) hydroxylase

- adrenogenital syndrome

- in males, penile enlargement rarely detected

- hyperplasia of adrenal cortex

- 2/3 have hypoatremia (Na) and hyperkalemia (K)

- treatment: cortisol which lowers ACTH so androgen production is normal

1. Male intersex A--> 46 XY

- no uterus/fallopian duct/wolffian duct

- testes are non-decended in abdomen

- amenorrhea

2. Male intersex B--> 46 XY

- partially a woman with wolffian sturcture/ testes are non-decended

- sometimes hypospadia (urethra opening on penis)

- cause 5α-reductase type 2 deficiency

* no conversion of testosterone to dihydrotestosterone

* raised as females until puberty

* autosomal recessive

1. suspicion of recognized syndrome

2. unexplained mental retardation

3. unexplained congenital malformation

4. pregnancy loss/infertility

5. abnormality in sexual development

6. malignancies

**detects large chromosomal changes: not good for detecting point mutations**