What is Division of a chromosome perpendicular to the normal axis of division leads to: and explain in detail?
Ans. b. Isochromosome (Ref: Robbins 9/e p160, 8/e p161)IsochromosomeIsochromosome formation results when one arm of a chromosome is lost and the remaining arm is duplicated, resulting in a chromosome consisting of two short arms only or of two long armsQ.An isochromosome has morphologically identical genetic information in both armsQ.MC isochromosome present in live births involves the long arm of the X and is designated i(X)(q10)Q.The Xq isochromosome is associated with monosomy for genes on the short arm of X and with trisomy for genes on the long arm of X.Ring ChromosomeA ring chromosome is a special form of deletionQ.It is produced when a break occurs at both ends of a chromosome with fusion of the damaged endsQ.If significant genetic material is lost, phenotypic abnormalities result. This might be expressed as 46,XY,r(14).Ring chromosomes do not behave normally in meiosis or mitosis and usually result in serious consequencesQ.Types of ChromosomeMetacentric:X-Shaped chromosomesCentromere in the middle so that the two arms of the chromosomes are almost equalQ.In a normal karyotype, two chromosomes are considered metacentric: chromosomes 1 and 3.Submetacentrie:If arms' lengths are unequal, the chromosome is said to be submetacentricCentromere is near the middle of the chromosomeOne arm is shorter than otherAcrocentric:If the p (short) arm is so short that it is hard to observe, but still present, then the chromosome is acrocentricQThe human genome includes six acrocentric chromosomes: 13, 14, 15, 21, 22 and Y chromosome.Telocentric:A telocentric chromosome's centromere is located at the terminal end of the chromosome.Telomeres may extend from both ends of the chromosomeQ.Humans do not possess telocentric chromosomesQ.