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Chapter 2

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BIOL 2000
Joseph Rasmussen

Chapter 2 Definitions Mitosis- cell division that produces two daughter cells with identical nuclei to the parent cell Meiosis- a process consisting of two consecutive cell divisions that produces daughter cells (gametes or sexual spores) with hald the genetic material of the parent Meiocyte- a diploid cell about to undergo meiosis Chromatid- one of two daughter DNA molecules produced by chromosome replication Dyad- a chromosome with two chromatids; double stranded chromosomes Homologous pair- Chromosomes that pair with each other at meiosis and contain the same genes (may have different alleles) Bivalent- two homologous chromosomes paired in Meiosis I Tetrad- four chromatids that make up a bivalent Synaptonemal complex- complex that allows chromosome pairing during Prophase I Kinetochore- proteins that attach the centromere to the kinetochore microtubules Reduction division- division that results in cells with one member of each homologous pair Crossing over- the exchange between homologous chromosomes of parts of a chromatid through breakage and rejoining Restriction fragment length polymorphism (RFLP)- change to DNA sequence changes ability of a restriction enzyme to cut DNA Null allele- complete loss of gene function Leaky allele- partial loss of gene function Silent allele- no change to gene function Mendels Hypothesis  Suggest parents contain 2 alleles, and gametes are 1 allele  Gametes fuse to regenerate diploid in progeny  What processes explain these ideas? o Alternating mitotic and meiotic divisions during eukaryotic life cycles account for Mendel’s diploid to haploid transitions o Animal cycle diploid (start with 2 diploid and end with haploid) o Fungus- haploid (start with haploid and end with haploid) o Plant- alternating haploid and diploid  What mechanism accounts for separation of alleles into gametes? o Mitosis and meiosis Stages of the asexual cycle  Interphase is the entire asexual cycle- Mitosis (M), G1, S (duplication) and G2  During the S phase, DNA molecules replicate to form identical chromatids  Chromatids are linked together until mitosis/meisosis  What ever DNA is present in the parent, the daughter cell has the same  b+ indicates wild type allele o Has GC sequence  b indicates mutant allele o Has AT sequence (mutant creates change in sequencing.)  G1 follows mitosis, provides checkpoints to ensure division is happening properly  G2 comes before mitosis  Replicated chromosomes are segregated into daughter cells in an organized fashion during: o Mitosis- generates cells identical to mother cell  Regardless of diploid or haploid parent cells o Meiosis- generates haploid cells from diploid Stages of Mitosis o Interphase o Early mitotic prophase o Late mitotic prophase o Mitotic metaphase o Mitotic anaphase o Mitotic teloplase  Interphase= G1, S, G2 (growth + DNA replcaition)  Prophase= chromosome condensation, break down of nuclear membrane  Metaphase= alignment of chromosomes along metaphase plate o Alignment requires action of kinetochore microtubules attached to centromeres  Anaphase= separation of chromosomes  Telophase= cytokensis, reformation of nuclear membrane o Mitosis generates daughter cells
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