Ch 6.1 Chromosomes

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Ch 6.1 Chromosomes

1. Nucleus contains chromosomes
2. Chromosome composed of genes
3. Genes are segments of DNA that code for proteins

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Draw a chromosome.

• A chromosome is made up of a DNA.

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• A replicated chromosome consists of two strands
  of identical chromosomal material called
  chromatids (sister chromatids).

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• A chromatid is a chromatid as long as it is held
  in association with a sister chromatid at the
  centromere.

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Homologous chromosomeschromosome pairs one
from each parent
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Chromosome number

• Example In humans, each body cell contains 46
  chromosomes (23 pairs).
• Pairs 1 22 are autosomes
• Pair 23 are sex chromosomes (X and Y).
• Picture of chromosomes is called a karyotype.
• Chromosomes arranged by size
• Way to detect abnormalities in chromosome number

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Trisomy 21

• Condition when a human has more than two copies
  of chromosome 21
• Results in Down Syndrome
• Occurs because of nondisjunction-one chromosome
  fails to separate properly during cell division

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Chromosome numbers

• Two sets of chromosomes is called the diploid
  number (2n46) found in body/somatic cells
• One set of chromosomes is called the haploid
  number (n23) found ONLY in sex cells/gametes
  (egg and sperm/pollen)
• One haploid sperm cell and one haploid egg cell
  make one diploid fertilized egg or ZYGOTE

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Chromosomal mutations

• Mutation-changes in an organisms chromosome
  structure
• Deletion
• a piece of a chromosome breaks off completely
• The new cell will lack a certain set of genes
• Duplication
• a chromosome fragment attaches to its homologous
  chromosome, which will then carry two copies of a
  certain set of genes

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Chromosome mutations

• 3. Inversion
• A chromosome piece reattaches to the original
  chromosome but in a reverse orientation
• 4. Translocation
• A chromosome piece reattaches to a nonhomologous
  chromosome

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Cell Division/Reproduction

• Process by which cells grow and divide.
• In prokaryotes binary fission is used to divide
  one cell into two identical cells.
• Copy DNA and divide cytoplasm.
• In eukaryotes divide one cell into two cells.
• Copy DNA and divide both cytoplasm and nucleus.

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Binary Fission

• In prokaryotic cells, there is only one
  chromosome attached to the inside of the cell
  membrane. DNA is circular.
• A form of asexual reproduction
• Binary fission-one parent passes exact copies of
  all its DNA to its offspring

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Ch 6.2 The Cell Cycle

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Cell Cycle

• The dividing and non-dividing stages in the life
  of a cell.
• Phases
• Interphase Growth and DNA replication
• Prophase
• Metaphase
• Anaphase
• Telophase

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Interphase

• Nucleus and nucleolus visible.

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Interphase

• Comprises about 90 of the cell cycle.
• Cellular growth
• Protein synthesis
• Metabolic activities
• DNA synthesis
• Made up of three phases
• G1 phase
• S phase
• G2 phase

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Interphase

• G1 (gap) phase
• Growth, protein synthesis and metabolic
  activities.
• Most cell are arrested in this phase.
• S phase (synthesis)
• DNA replication takes place.
• 3. G2 (gap) phase
• a. Preparation for Mitosis phase

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Cancerous cells...

• 1.Divide too many times
• Masses of cells
• tumors
• benign
• malignant

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Ch 6.3 Mitosis Cytokinesis
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Cell cycle Mitosis

• The form of cell division by which a eukaryotic
  somatic/body cell duplicates.
• Mitosis is asexual reproduction.
• Cell division is the continuation of life based
  on the growth and reproduction of cells

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Somatic/body cell Reproduction

• Somatic cells are all body cells (like nerve,
  liver, etc...) except sperm and ova (egg) cells.
• All body cells have the same number of
  chromosomes.

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Mitotic Phase

• Mitosis (karyokinesis)
• Nuclear division of genetic material.
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis
• Cytoplasmic division.

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Prophase

• Longest phase of mitosis
• Nucleolus disappears
• Chromatin material condenses into chromosomes,
  consisting of two sister chromatids.

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Prophase

• Centrioles move apart (not found in plants).
• Spindle fibers form and attach from centrioles to
  centromeres by kinetochores.
• Nuclear envelope fragments and disappears.

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Prophase

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Prophase
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Metaphase

• Shortest phase
• Centrioles are at opposite ends of the cell.
• Spindle fibers attached to centrioles and
  centromeres.
• Chromosomes move to the metaphase
  plate/equatorial plate/center of cell

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Metaphase

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Metaphase

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Anaphase

• Centromeres uncouple and spindle fibers shorten.
• Sister chromatids separate and move apart.
• After separation, chromatids are now considered
  chromosomes.

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Anaphase

• During this phase, the cell contains twice the
  normal number of chromosomes.
• Cell begins to elongate.
• At the end, there are equal numbers of
  chromosomes at the poles.

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Anaphase
No longer sister chromatids, now chromosomes

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Anaphase
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Telophase

• Cleavage furrow develops in animal cells
  (Cytokinesis begins).
• Cell plate develops in plants (no cleavage
  furrows in plants).
• Nucleolus reappears.

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Telophase

• Nuclear membrane reappears.
• Chromosomes uncoil.
• Spindle dissolves.
• In the end, two genetically identical nuclei
  (karyokinesis completed) are present.

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Telophase
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Telophase
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Cytokinesis

• Cytoplasmic division
• Cell plate complete in plants
• In the end, two separate daughter cells produced
  with single nucleus.

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Cytokinesis
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Question

• A cell containing 20 chromosomes at the beginning
  of mitosis would, at its completion, produce
  cells containing how many chromosomes each?

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Answer

• 20 chromosomes

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Question

• A cell containing 40 chromatids at the beginning
  of mitosis would, at its completion, produce
  cells containing how many chromosomes each?

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Answer

• 20 chromosomes

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Importance of mitosis

• Maintain cell growth and repair in multicellular
  organisms for reproduction in unicellular
  organisms.
• Daughter cells formed by mitosis are genetically
  identical. Why? Same DNA.
• What about reproduction in multicellular
  organisms? Meiosis-cell division of reproductive
  cells.

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Cell Cycle Video

• http//www.cellsalive.com/cell_cycle.htm

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Mitosis Video

• http//www.cellsalive.com/mitosis.htm