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Lecture 12

BIL 250 Lecture 12: ch2 part2

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University of Miami
BIL 250

Prokaryotic Organisms: two major groups; lack a nuclear envelope and membranous organelles Eubacteria Nucleoid: unenclosed region where the genetic material is present as a long circular DNA molecule that is compacted Archaea Do not have a distinct nucleolus but do contain genes that specify rRNA molecules Chromosomes Exist in Homologous Pairs in Diploid Organisms Chromosomes are most easily visualized during mitosis Centromere: constricted region of the chromosome; location establishes the general appearance of each chromosome Different arm ratios are produced Meta centric Submetacentric Acrocentric Telocentric Shorter arm – p arm (petite) Longer arm – q arm All somatic cells derived from members of the same species contain an identical number of chromosomes – diploid number (2n) Meiosis converts the diploid number of a chromosome to the haploid number Following fusion of two gametes, the diploid number is reestablished Homologous Chromosomes: for each chromosome exhibiting a specific length and centromere placement, another exists with identical features Exceptions: many bacteria and viruses have but one chromosomes; yeasts and molds, and certain plants like bryophytes spend the predominant stage of their lives in a haploid state Locus: gene sites homologous chromosomes contain identical sites Biparental Inheritance: each diploid organism contains two copies of each gene Alleles: different alternative forms of the same gene Karyotype: photograph of mitotic chromosomes matched up and displayed Human karyotype – each of the 46 chromosomes is clearly a double structure consisting of two parallel sister chromatids connected by a common centromere Haploid Number (n): equal to
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