Download Chapter 10 / Chromosomes, Mitosis, and Meiosis I. Introduction

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Chapter 10 / Chromosomes, Mitosis, and Meiosis
I. Introduction
• how DNA is stored and how it gets ready to be copied
• the normal life cycle of a cell
• division of cells to make new cells
II. Chromosomes
A. Structure
1. DNA in eukaryotic cells is packaged into bundles called chromosomes
2. located in the nucleus
3. consists of condensed, wound bundles of chromatin
4. chromosomes form when a cell is ready to divide
B. Information storage
1. information for particular traits (e.g., eye color) is stored on regions of DNA called genes
2. concept of gene developed before exact structure of DNA was known
3. genes carry codes to make a single protein or many proteins
4. one or many genes may determine a particular trait
5. genes can be turned on or off
6. genes are passed on
C. Variation between different organisms
1. all individuals of a particular species of organism have the same normal number of
chromosomes per cell
--determined through karyotyping
2. different species could have the same number of
chromosomes
3. the information carried on the chromosomes is what makes each species (and each individual)
unique
4. exist in pairs called homologous chromosomes
diploid
haploid
III. The Cell Cycle
• cells grow, develop, and divide
• cells often divide when they reach a certain size
• generation time (T)
• Cell cycle can be divided into 2 main stages: interphase and cell division
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A. Interphase
-- the stage between cell divisions
1. G1 phase (first gap phase)
a. growth
b. substances required for making DNA are produced
2. S phase (synthesis phase)
DNA is replicated
3. G2 phase (second gap phase)
a. growth
b. substances required for cell division are produced
B. Cell Division
1. Mitosis
can be divided into different stages
a. prophase
chromosomes become visible:
sister chromatids
mitotic spindle
b. metaphase
chromosomes are lined up in the middle of cell
c. anaphase
sister chromatids get “pulled” apart
d. telophase
return to interphase
nuclear structures reappear
2. cytokinesis
division of cytoplasm
center of cell “pinches in”
new cell membrane forms
Result is two new cells that are genetically identical (clones)
IV. Different Types of Reproduction
A. Asexual
1. single parent splits to form identical individual—involves MITOSIS
2. genetically identical
3. can occur quickly, but no variation
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B. Sexual
1. union of 2 genetically distinct cells (gametes)
2. offspring produced = the zygote
3. gametes
a. genetically different from the original cell that produced them
b. have half the number of chromosomes
haploid
diploid
homologous chromosomes
c. produced by a special type of cell division involving MEIOSIS
V. Meiosis
diploid cells→haploid cells
2 nuclear and cytoplasmic divisions:
Meiosis I, Meiosis II
each has a prophase, metaphase, anaphase, telophase
A. Meiosis I
1. chromosomes duplicated in interphase→sister chromatids
2. homologous chromosomes pair
synapsis
tetrad
3. crossing over occurs
4. homologous chromosomes separate during anaphase I
Now have 2 cells:
each has 1 set of the homologous chromosomes (haploid)
remember: this set still contains sister chromatids (duplicates)
B. Meiosis II
similar to mitosis except starting with haploid cells
1. chromosomes (sister chromatids) line up on equatorial plane
2. sister chromatids separate
3. new cells formed are haploid; all (total of 4) are genetically distinct form the original cell
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