Genetics Lecture Notes: Chromosome Structure & Organization PDF

Genetics Dr\ Hassnaa Hiessen Lect.1 chromosome structure& orGanization Chromosomes; darkly stained, rod shaped bodies visible under light microscope in a cell during metaphase stage Features of eukaryotic chromosomes...

Genetics Dr\ Hassnaa Hiessen Lect.1 chromosome structure& orGanization Chromosomes; darkly stained, rod shaped bodies visible under light microscope in a cell during metaphase stage Features of eukaryotic chromosomes Not visible during interphase but clearly visible during mitotic metaphase under light microscope Bear genes so transmit characters from generation to generation. Vary in shape, size and number in different species Have property of self-duplication, segregation and mutation. Composed of DNA, RNA and histones Chromosome number; The number of chromosomes varies from species to species but generally the number is constant within a species. Somatic cell Sex cell or gametic cell Any cell other sex cell for example kidney Ova and sperm contain only one , muscle ,skin …etc complete set of chromosome Contain diploid cell (2n). haploid cell (1n) Chromosomes in each cell classified into: 1. Autosomes 2. sex chromosomes ✓ all chromosomes exclusive of the ✓ which are heteromorphic pair of sex chromosomes chromosomes called (XX and XY) ✓ equal (2n-2) in somatic cell ✓ equal 2 in somatic cell & ( n-1) in gametes and 1 in gametes. A genome is a set of chromosomes corresponding to the haploid set (n) of a species ❖ With the exception of sex chromosomes, each chromosome exists in pairs with same length and centromere placement, identical features and the members of each pair are called homologous chromosomes. ❖ One member of each pair is derived from the maternal parent (through ovum) and the other member is derived from the paternal parent (through the sperm). 1|Page Genetics Dr\ Hassnaa Hiessen Lect.1 Homologues chromosome; ✓ Chromosomes that matched in ; *size, *position of the centromere (shape) and have the same genes but not necessarily the same alleles, at the same locus. ✓ Chromosomes that are paired during the production of gametes in meiosis CHROMOSOME MORPHOLOGY ; 1. Centromere 2. Chromatids 3. secondary constriction and satellite 4. Chromonema 2|Page Genetics Dr\ Hassnaa Hiessen Lect.1 5. Chromomere 6. Telomere 7. Matrix Centromere The region of chromosome with which spindle fibers are (primary constriction( attached during metaphase. )kinetochore) Chromatid ▪ One of the two distinct longitudinal subunits of a chromosome which get separated during anaphase. ▪ Two chromatids of a chromosome are held together by centromere. ▪ After separation at anaphase each chromatid becomes a chromosome. Telomere The terminal region of a chromosome on either sides. Maintain the stability of chromosome (telomere of one chromosome cannot unite with the telomere of another chromosome). Secondary Constriction has constant position and, therefore, can be used as useful marker. Chromomeres It is bead like structures found on the chromosomes. Chromonema thread like coiled structures (DNA thread) and it is the gene bearing portion of chromosomes Matrix o A mass in which chromonema are embedded. o Matrix is enclosed in a sheath which is known as pellicle. o Both matrix and pellicle are non genetic materials. 3|Page