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Lecture 2

Chromosomes_and_Sex_Linkage Lecture 2 Notes

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Department
Molecular Biology and Genetics
Course
MBG 2040
Professor
All Professors
Semester
Fall

Description
Lecture Set 2 Chromosomes and Sex LinkageEukaryotic chromosomes are made of chromatin which is a complex of DNA and proteinsChromosomes are dynamic pieces of chromatin that can alternate between tight and loose compactionoChromosomes are highly compacted during mitosis and meisosisoChromosomes can only be visualized when they are highly compactedChromosomes occupy specific regions of a nucleus called chromosome territoriesThese territories are specific and distinct subdomainsterritories within the nucleusChromatin is found in two varieties Heterochromatin ConstitutiveEuchromatinHighly condensedLess condensedGene poorGene richTypically at centromeres and telomeresAt chromosome armsNo meitotic recombinationRecombination at meiosisStains dark in karyotypingStains lighter in karyotypingKaryotypingA karyotype is the number and appearance of chromosomes from a eukaryotic somatic cell To do karyotyping chromosomes must be compacted and the cells must be mitoticThe chromosomes in a karyotype are from cells that have been arrested in mitosis and each chromosome consists of two identical sister chromatidsoWBCs are a common choice for human karyotyping because they are easily induced to divide and grow in tissue cultureThe studyvisualization of karyotypes is made possible by staining usually using a dye called GiemsaoConstitutive heterochromatin stains darker than euchromatinSex ChromosomesHumans have one pair of sex chromosomes XX females or XY malesMales are heterogametic sex chromosomes are not the same XY while females are homogametic XXThe Y chromosome has the SRY gene which encodes TDF testis determining factorThere are 300 genes on the human Y chromosome and over 1000 genes on the human X chromosomeMuch of the Y chromosome is heterochromatic consisting of highly repetitive noncoding DNAThe X and Y chromosomes form a homologous pair though Y is much shorter than XSpecies other than humans have different kinds of sex chromosomes
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