Short notes
Sex chromosomal aberration
Sex Chromosomal Aberration
Definition
Understanding evolutionary change through chromosomal studies.
Example / case study
- Humans and chimpanzees share a common ancestor with 24 pairs of chromosomes;
- two fused to form chromosome #2 in humans.
- Discovered by: Murray F. Lyon (Lyon Hypothesis, 1961). (T: M.F Leone)
- Refers to the inactivated X chromosome in female somatic cells (random inactivation).
Klinefelter (Xxy)
Definition
A karyotype is the complete set of chromosomes of an individual, arranged in homologous pairs according to their size, shape and banding pattern.
Example / case study
- Cri-du-chat Syndrome (5p−) – deletion on short arm of chromosome 5.
- The brain is highly sensitive to gene dosage imbalance.
Thinkers
- Turner’s Syndrome (XO): Female with only one X → no Barr body.
Turner (Xo)
Definition
A karyotype is the complete set of chromosomes of an individual, arranged in homologous pairs according to their size, shape and banding pattern.
Example / case study
- Cri-du-chat Syndrome (5p−) – deletion on short arm of chromosome 5.
- Severity depends on proportion and distribution of abnormal cells.
- Mosaic Down Syndrome – some cells 47,+21; others normal 46.
- Turner mosaic – some cells 45,X; others 46,XX.
Thinkers
- Turner’s Syndrome (XO): Female with only one X → no Barr body.
Super Female (Xxx)
Definition
Refers to the inactivated X chromosome in female somatic cells (random inactivation).
Example / case study
- Calico Cats: Different coat patches due to random X inactivation.
- Turner’s Syndrome (XO): Female with only one X → no Barr body.
Intersex
Definition
Diagnosis: Karyotype (47,XXX); two Barr bodies.
Example / case study
- Cri-du-chat Syndrome (5p−) – deletion on short arm of chromosome 5.
- Baby after birth cry like cat, microcephaly, wide-set eyes, low-set ears.
- Intellectual disability, delayed development.
Other Syndromic Disorders
Definition
Understanding evolutionary change through chromosomal studies.
Example / case study
- Humans and chimpanzees share a common ancestor with 24 pairs of chromosomes;
- two fused to form chromosome #2 in humans.
- Discovered by: Murray F. Lyon (Lyon Hypothesis, 1961). (T: M.F Leone)
- Refers to the inactivated X chromosome in female somatic cells (random inactivation).