Genes, Chromosomes, and the mechanism of mendelian Inheritance Cells reproduce via a cell cycle Meiosis is the key to sexual reproduction and Mendel's rules Sex determination, sex linkage and chromosome nondisjunction supported the chromosome theory
Genes, Chromosomes, and the mechanism of Mendelian Inheritance • Cells reproduce via a cell cycle • Meiosis is the key to sexual reproduction and Mendel’s rules • Sex determination, sex linkage and chromosome nondisjunction supported the chromosome theory
Metaphase chromosomes Pair of homologous Pair of homologous metacentric chromosomes acrocentric chromosomes Centromere Centromere Sister Nonsister chromatids chromatids Nonhomologous chromosomes Homologous chromosomes Homologous chromosomes
(a)Cell cycle M The cell cycle interpet mosome /cation G1: interphase, gap before duplication B b S: DNA synthesis and chromosome duplication A 日 Go: interphase, gap B before m mitosis a B bb
Cells reproduce by a cell cycle Cells in the body reproduce by mitosis 6.⑤ Mitosis produces cells with exact G Cytokinesis First gap copies of the parental cell Telophase s chromosomes and Synthesis Mitosis genes. Interphase Second gap
Cells reproduce by a cell cycle • Cells in the body reproduce by mitosis. • Mitosis produces cells with exact copies of the parental cell chromosomes and genes. Fig. 3.1
Contractile ring Cleavage furrow Cell late
Cell cycle checkpoints Chromosome and · Have the Is cell of sufficient size? centrosome duplication chromosomes been Have proper signals from environment been received completely duplicated? THEN: Decision to duplicate THEN: Decision to chromosomes and enter mitosis centrosomes Prophase Interphase Mitosis Ongoing protein synthesis and e Metaphase cell growth N Have all chromosomes Telophase arrived and aligned at and the metaphase plate? cytokinesis Anaphase THEN: Decision to initiate anaphase
Sexual reproduction: Meiosis Germ cells undergo two special nuclear divisions with only one chromosome replication These meiotic divisions reduce the number of chromosomes in the gametes Chromosome behavior in meiosis is the first evidence that genes reside on chromosomes
Sexual reproduction: Meiosis • Germ cells undergo two special nuclear divisions with only one chromosome replication. • These meiotic divisions reduce the number of chromosomes in the gametes. • Chromosome behavior in meiosis is the first evidence that genes reside on chromosomes
Drosophila melanogaster X Diploid cells X 2n=8 Haploid cells (gametes) n=4
Meiosis: An overview 2n Chromosomes duplicate Meiosis i No duplication Meiosis l No duplication n
Meiosis I a. Earty prophase I ORient chromosome During prophase I, homologous chromosomes condense The condensing chromosomes farst become visible during earty prophase I(in the leptotene substage), and the paIr s besome fully con (becoming bivalents), and recombine Each chromosome hAs twe chron. The bivalents attach to spindle fibers. During anaphase I the homologous During telophase I two daughter nuclei form m,可ane Each of the two daughter cells from meiosis I chromosome from esch bivalent nters meiosis I
Meiosis I • During prophase I, homologous chromosomes condense, pair (becoming bivalents), and recombine. • The bivalents attach to spindle fibers
