Prabha Batwal Biology Lecturer CHAPTER 3 INHERITANCE AND VARIATION PART3 Chromosomes Chromosomes are filamentous bodies present in Eukaryotic cell Their size varies from species to species ID: 1032519
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1. ARIHANT COLLEGE OF ARTS,COMMERCE & SCIENCEPrabha BatwalBiology Lecturer
2. CHAPTER -3 INHERITANCE AND VARIATION (PART3)
3. ChromosomesChromosomes are filamentous bodies present in Eukaryotic cell. Their size varies from species to species.They are self replicating and play vital role in heredity, mutation, variation, and evolutionary development of eukaryotes.Chemically made up of DNA, histone and non-histone proteins.Chromosomes are carries of heredity .
4. Number of ChromosomesThe no of chromosomes varies from species to species.It may be Euploidy and AneuploidyEuploidy- When chromosome no is exact multiple of primary no. e.g. n = haploid (one set of chromosome), 2n= diploid ,3n= triploid so on.
5. Aneuploidy – when chromosome no is not the exact multiple of the haploid set. e.g. Monosomy(2n-1), nullisomy(2n-2), trisomy(2n+1) and tetrasomy(2n+2).
6. Structure of ChromosomeChromosomes are best visible in metaphase stage as they are highly condensed in that stage.Consists of two chromatids joined together at centromere(primary constriction), which consit of a disk shape plate called kinetochore. Few chromosomes posses secondary constriction.Each chromatid contains a long , unbranched, slender, highly coiled DNA thread called Chromonema.Chromatid consits of double standard DNA molecule.
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8. Types of ChromosomesDepending upon the position of Centromere four tyopes (shapes) of chromosomes are thereAcrocentric ( j shaped )Telocentric ( i shaped )Submetacentric (L shaped )Metacentric (V shaped )The ends of chromatids are known as Telomeres.
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10. Sex ChromosomesThe chromosomes which are responsible for the determination of sex.Human being and other mammals have X & Y chromosomes as sex chromosomes.X chromosomes is straight, rod like and longer than Y chromosome. X chromosome is metacentric, Y is acrocentric.X has large amount of euchromatin & small amount of heterochromatin. Euchromatin has large amount of DNA material, hence it is genetically active. Vice versa with Y chromosomes, hence genetically less active.
11. Structure of X and Y Chromosomes
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