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Chapter 3

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Fiona Rawle

Chapter 3Chromosomal Basis of InheritancePrinciple PointsDiploid eukaryotic cells have 2 haploid sets of chromosomesone set comes from each parentcomplete set of chromosomes in a eukaryotic cell is called its KaryotypeMitosisnuclear division in eukaryotic cellsrepresented by M in cell cycleresults in daughter nuclei that contain identical chromosome numbersare genetically identical to one anotherMeiosisoccurs in all sexually reproducing eukaryotesspecialized diploid cell with 2 haploid sets of chromosomes is transformed through one round of DNA replication then 2 rounds of nuclear division into 4 haploid cells each with one set of chromosomesgenerates genetic variability through which maternalpaternal chromosomes are reassortedChromosome theory of inheritance genes are located on chromosomesIn organisms with sex chromosomesone sex is homogametic female XXthe other sex is heterogametic male XYsex determination is related to the sex chromosomesY chromosome specifies malenessAbsence of Y chromosome results in femalenessAllele responsible for a trait can be inherited in 1 of 5 main ways in humans1autosomal recessive2autosomal dominant3Xlinked recessive4Xlinked dominant5YlinkedChromosomes and Cellular ReproductionEukaryotic ChromosomesNumber of chromosomes is characteristic of the speciesmany eukaryotes have 2 copies of each type of chromosome in their nucleichromosome complement is said to be diploid 2Ndiploid is produced by the fusion of 2 haploid gametes mature reproductive cells that are specialized for sexual fusionDiploid 2N A cell or an individual with 2 copies of a chromosome1Zygote The cell produced by the fusion of a female gamete egg and a male gamete spermHaploid N Each gamete has only one set of chromosomesGenome Complete compendium of genetic information in a haploid chromosome setHomologous Chromosomes members of a chromosome pair that contain the same genespair during meiosis in diploid organismsHomolog each member of a pair of homologous chromosomes Nonhomologous Chromosomes Chromosomes that contain different genesdo not pair during meiosis Malefemale cells are distinct with respect to their complement of sex chromosomesthe chromosomes that are represented differently in the 2 sexes in many eukaryotic organismsone sex has a matched pairother sex has unmatched pairhuman females have 2 X chromosomes XXhuman males have 1 X and 1Y chromosome XYAutosomes Chromosomes other than sex chromosomeshumans have 22 autosome pairs for a total of 44 autosomeseach chromosome has a constriction along its length called a Centromereimportant for behaviour of the chromosomes during cellular divisionlocation of the Centromere has 4 general positions useful for classifying eukaryotic chromosomes1Metacentric chromosomecentromere at about the center so chromosome appears to have 2 equal arms2Submetacentric chromosomeshave one arm longer than the other3Acrocentric chromosomeshave one arm with a stalkoften with a bulb called a satellite on it4Telocentric chromosomeshave only one arm bc the centromere is at the endKaryotype complete set of all the metaphase chromosomes in a cell consisting of 2 chromatids per chromosomeChromosomes at their most condensed in mitosis are used for identificationthey are the most compact form during cell division cycleeasy to see under microscope after stainingKaryotype is species specificCan be arranged in order to their sizeposition of the centromere particularly humansHuman chromosomes can be arranged in order according to their sizeposition of the centromereTotal of 46 chromosomes2
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