BIOLOGY 305 Study Guide - Fall 2019, Comprehensive Final Exam Notes - Gene, Phenotype, Mutation
BIOLOGY 305
Biology 305 Lecture 1: Meiosis & Mitosis
Reading. Introduction & Appendix Ch. 2
Types of Cell Division
• Mitosis: leads to the production of 2 cells, each with the same number of chromosomes as
the parental cell and the identical genetic content.
• Meiosis: reduces the genetic content and the number of chromosomes by half
Human Karyotype
• Autosomes numbered by size
• Dye used to help distinguish chromosomes based on banding pattern
• Female: XX
• Male: XY
• All somatic cells derived from members of the same species contain an identical number of
chromosomes
Chromosomes
• Each chromatid is a long piece of DNA
• 2 sister-chromatids = 1 chromosome;
sister chromatids are attached at
centromere
• Chromosomes have different names
based on where the centromere is
o Middle → metacentric
o Between middle and end →
sub-metacentric
o Close to end → acrocentric
o At end → telocentric
• P Arm: short
• Q Arm: long
• In many organisms, nearly all chromosomes exist in pairs with regard to chromosome
lengths and centromere placement. The members of each pair are called homologous
chromosomes
• Homologous chromosomes contain nearly identical genetic information
• An organism (cell) is defined as a diploid if each member of the chromosomes has just 2 (a
pair) of homologous chromosomes
o Human body (diploid) 2n=46 → 2 sets
o Egg or sperm (haploid) n=23 → 1 set
• Polyploids: cells or organisms having more than 2 sets of chromosomes
Mitosis
• Mitosis is critical to all eukaryotes
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• In sexually reproducing organisms, mitosis provides the mechanism for development and
growth
• In many unicellular organisms that reproduce asexually, mitosis provides the mechanism for
reproduction
• Interphase is the longest stage of the cell cycle
o G0 → optional stage where cells are stored for later
o G1 → 2n chromosomes
o S → 2n • 2 chromosomes
o G2 → cannot observer chromosomes
o Absence of visible chromosomes, nucleus is filled with chromatin fibers
• Mitosis is the shortest stage
o Prophase
▪ Migration of two pairs of centrioles to opposite ends of the cell
▪ Centrioles organize cytoplasmic microtubules into spindle fibers that run
between the two poles of the cell
▪ Nuclear envelope disappears
▪ Chromatins condense and chromosomes become visible; each chromosome
consists of 2 sister chromatids (2n•2)
o Prometaphase
▪ Migration of each chromosome to the equatorial place of the cell, lef by the
centromeric region
o Metaphase
▪ Kinetochore: connects chromosome to spindle fiber at the centromere
▪ Configuration of chromosomes at the equatorial plane, following the
chromosomal migration. At the end of the metaphase, each centromere is
aligned at the place
o Anaphase
▪ Sister chromatids disjoin from each other and migrate to opposite ends of
the cell
▪ Once anaphase occurs, each chromatid is referred to as a daughter
chromosomes (2n)
o Telophase
▪ Cytokinesis: Division of the cytoplasm
▪ Animals: constriction of the cytoplasm
▪ Plants: a cell plate is synthesized and laid down in the region of the
metaphase plate
▪ In late telophase, nuclear envelop reforms and chromosomes uncoil
Regulation
• Cell cycle is genetically regulated
• G1 Checkpoint:
o Check for nutrients, growth factors, DNA damage
o P53 gene is involved here (LOOK UP MORE)
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