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Bio Exam II

Meiosis

TermDefinition
intro to heredity - heredity: traits from one gen. to the next - variation: difference b/w individuals - genetics: study of heredity & heredity variation - gametes: reproductive cells
asexual reproduction - single parent produces offspring - unicellular split - multicellular budding or fragmentation
In Eukaryotes via... - Mitotic division - 1 diploid (2n) parent= 2 diploid offspring - 1 haploid (n) parent= 2 haploid - produces clones= offspring genetically identical
Advantages of Sexual Reproduction - fast - low E - safe - lots of offspring - well adapted? don't change
Sexual Reproduction - fusion of 2 gametes form a zygote - gamete (n) + gamete (n) = fertilization= zygote (2n) - gametes usually from diff. parents (not always)
Disadvantages of Sexual Reproduction - slow - high E - dangerous (preditation disease) - fewer offspring - wel adapted? offspring only gets. 5 of genes (genome dilution)
Advantages of sexual reproduction - genetic variation - offspring; combo of parent's genes - better able to respond to stress
If gametes have same chromosome # as parents... - chromosome # doubles - solution: meiosis - reduction division: cell divides twice - 1 diploid (2n) cell= 4 haploid (n) cells
Chromosomes in Heredity - Karyotype: display of chromosomes - mitotic chromosomes, stained - Human Karyotype - somatic cells: 46 chromsomes - 22 pairs of autosomes
Chromosomes in Heredity pt.2 - sex chromosomes: X & Y; determine sex; female XX; Male XY - small homologous region in X & Y chromosomes - Homologous chromosomes - same length, centromere position, staining pattern - homologous chromosomes contain the same genes
Life cycles - life cycles: sequence of stages from gen to gen - fertilization & meiosis: - occur in all sexual life cycles - alternative - timing varies
Variety in Sexual - life cycles - n & 2n cells can undergo mitosis; only 2n cells can undergo meiosis
Meiosis - reduction & division - 4 stages & involves 2 cell divisions: - interphase, meiosis I , interkinesis, Meiosis II
Interphase - chromosome & centrioles duplicate - each chromosome now 2 sister chromatids ( still chromatin) - in humans 2n=46; so 92 chromatids enter meiosis
Meiosis I & cytokinesis - first meiotic division- homologous chromosomes separate, ploidy reduced
Prophase I - crossing over - synapses; homologous chromosomes pair up - gene in chromosome align - synaptomal complex a forms- protein structure - results in tetrad: 2 homologous chromosomes (4 chromatids) held together
Point of Synapsis - crossing over (homologous recombination - enzymes break & rejoin DNA - exchanges b/w non-sister chromatids
Prophase I pt.2 - chromatin condenses - centromeres & kinetochores of homologous chromosomes separate - nuclear envelope breaks down, spindle forms
Metaphase I - tetrads align - homologous chromosomes orient towards opposite poles - both sister kinetochores of one chromosome= spindle for same pole - kinetochores of homologous chromosomes= spindle for opposite poles
Anaphase I - Disjunction: Homologous chromosomes separate - sister chromatids still connected - chromosomes act independently - direction depends on orientation of tetrad
Non Disjunction - non disjunction - homologs fail to separate - 2 homologs go to same place - relatively common
Telophase I - chromosomes may de-condense - nuclear envelope might reform - cytokinesis occurs - results in 2 haploid cells, each has duplicated chromosomes
Interkinesis - time b/w 1st & 2nd meiotic division - short (interphase like stage) - no s phase
Meiosis II -2nd meiotic division - chromatids separate into daughter cells - very. sim. to mitosis II - Prohase II - Metaphase II - Anaphase II - Telophase II
Start & Stop - Start: 2 cells, n, duplicated chromosomes - End: 4 cells, n, unduplicated chromosomes
Created by: tennadeleta.