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Biology PP16

meiosis

QuestionAnswer
gametes (eggs and sperm) contain half the complement of chromosomes found in other cells
fertilization fusion of gametes
zygote contains two copies of each chromosome
n = ? 2n = ? 23; 46
Meiosis 1 separates the two homologs
meiosis II separates the two sister chromatids
prophase I chromosomes condense (coil); nuclear membrane breaks down; homologous chromosomes undergo synapsis (pair up); cross over occurs (recombination) and chromsomes exchange segments
metaphase I homologous chrosome pairs line up at random at the equatorial midline; microtubules attach to centromeres
anaphase I centromeres do not divide; homologs separate and move to opposite poles
telophas I nuclear membrane reforms; chromosomes uncoil; after cytokinesis two haploid cells are produced
meiosis II similar to mitosis but with two main differences: 1) Haploid set of chromosomes 2) Sister chromatids are not identical because of cross over
Prophase II chromosomes coil; spindle forms; nuclear membrane breaks down; each chromosome is composed of two sister chromatids attached at the centromere
metaphase II chromosomes line up on the midline and attach to spindle fibers
anaphase II centromeres divide; sister chromatids move to opposite poles
telophase II nuclear membrane reforms; chromosomes uncoil; after cytokinesis four unique haploid cells are produced.
synapsis homologous chromosomes pair along their lengths in prophase I; cross over
reduction division homologs separate in anaphase I reducing chromosome # to 1n- this produces haploid gametes
3 key mechanism that increase genetic diversity crossing over; independent assortment; random fertilization
crossing over DNA exchanges between chromatid pairs
nondisjunction members of a chromosome pair fail to separate during anaphase
aneuploidy -extra chromosome or missing a chromosome
trisomy 21 Down syndrome - extra chromosome at chromosome 21
Created by: Tiffastic
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