NOTES ON GENETICS
Q.SHORT NOTE:- 5 Marks
1. It is a Basic tool of Cytogeneticist
2. Karyotype is a photographic representation in which chromosomes are arranged in order of decreasing length
3. Giemsa stain (G banding) technique—each chromosome can be seen to possess a distinctive pattern of alternating light and dark bands of variable widths
4. Shorthand of Cytogenetics:
5. Short arm denoted as p, long arm denoted q.
6. Each arm divided into numbered regions from the centromere onwards.
7. Each region numerically arranged into bands.
8. For e.g., 5p24 would denote chromosome 5, short arm, region 2 and band 4.
9. Cytogenetic disorders may result from structural or numeric abnormalities of chromosomes.
10. It may affect autosomes or sex chromosomes.
11. Applied ;-Cytogenetic Disorders involving Autosomes
a) Trisomy 21/Down’s syndrome most common chromosomal disorder.
b) Down syndrome is a chromosomal abnormality characterized by the presence of an extra copy of genetic material on the 21st chromosome
c) Trisomy 21 is caused by a meiotic nondisjunction event.
d) With nondisjunction, a gamete (i.e., a sperm or egg cell) is produced with an extra copy of chromosome 21; the gamete thus has 24 chromosomes
e) When combined with a normal gamete from the other parent, the embryo now has 47 chromosomes, with three copies of chromosome 21.
f) About 4% of cases are due to Robertsonian translocations.
g) Maternal age has a strong influence.
h) Karyotype for trisomy Down syndrome. Notice the three copies of chromosome 21
g:\anatomy pdf\notes\short notes karyotyping notes .docx
ONE OR TWO SENTENCES. 2 MARKS.
Q1.WHAT IS GENETICS?
ANS. A BRANCH OF BIOLOGICAL SCIENCE CONCERNED WITH THE STUDY OF THE CAUSE & NATURE OF SIMILARITY & DISSIMILARITY OF THE INDIVIDUALS RELATED BY COMMON ANCESTRY(HEREDITARY).