Chapter 11

Vocab:

• Chromatin: is the loose form of DNA decondensed- associated with histone proteins

• Chromosomes: consists of a long, thin DNA molecule that contains the genetic information for the organism (condensed DNA)- associated with histone proteins

• Histone proteins: positively charged proteins that bind to DNA (which is negatively charged) in the nucleus of a cell to help organize and compact it

• Diploid: 2n (2 sets/copies) copies of each chromosome, one copy inherited from each parent (4 chromosomes total)

  • n= number of chromosomes

• Haploid: 1n (1 copy/set) of each chromosome (2 chromosomes total)

• Sister chromatids: identical copies of a chromosome that are joined together at the centromere

• Homologous chromosomes: a pair of chromosomes similar in size/shape and carry the same genes but can have different alleles (versions of specific genes)

• Centromere: where the chromatids are held together

• Spindles: organelles composed of protein microtubules. They function in moving chromosomes during mitosis

• Somatic cells: all the cells of the body that are not specialized for reproduction (contain 2 sets of chromosomes, one chromosome from each parent)

• Chiasma: location on homologous chromosomes where crossing over occurs

• Synapsis: process where homologous pairs align their DNA sequences at similar alleles

• Independent assortment: the random alignment of homologous chromosomes at the metaphase plate during metaphase I of meiosis

11.1:

Prokaryotes:

• Divide by binary fission: the cell grows in size, replicates its DNA, and then separates the cytoplasm and DNA into two new genetically identical daughter cells

• Binary Fission Steps:

  • DNA replication in prokaryotes: When a cell divides, its chromosome (most prokaryotes have just one main chromosome) must be replicated, and each of the two new daughter cells must receive a copy.

  • DNA segregation in prokaryotes: When replication is complete, the two daughter DNA molecules separate and segregate from one another at opposite ends of the cell.

  • Cytokinesis: the cytoplasm divides and a protein called FtsZ pinches the cell in half, which separates the DNA molecules into 2 genetically identical daughter cells. each daughter cell has the same number of chromosomes as the parent cell

11.2/11.3:

Eukaryotes

• The phases through which a single cell passes to produce daughter cells by cell division are G1, S, G2, and M (The M phase includes mitosis and cytokinesis. The other three phases together make up interphase)

• Interphase: typical cell functions occur, including DNA/chromosome replication

  • G1 phase: cells grow in volume and carry out their normal functions

  • S phase: DNA replication (duplicating its chromosomes into 2 sister chromatids)

  • G2: continues growth and carrying out normal functions, spindle synthesis begins, and prepares for mitosis and cytokinesis.

  • G0: cells do not divide again once they reach maturity (the resting phase or gap phase, is a cellular state outside of the cell cycle where cells are not dividing or preparing to divide)

    ex: nerve (neurons) cells and heart cells

• Mitosis: the separation of chromosomes, resulting in diploid cells (2 genetically identical daughter cells)

  • Prophase:

    - condensation of sister chromatids

    - centrosomes migrate to opposite poles of the cell which allows microtubules to begin to form mitotic spindles

    - the nuclear membrane breaks down

    - the nucleolus disappears from the nucleus.

  • Metaphase: mitotic spindles align chromosomes in the middle of the cell in a line

  • Anaphase: sister chromatid pairs are pulled apart by the spindle fibers. the separated chromatids (daughter chromosomes) move toward opposite poles (to opposite ends of the cell)

  • Telophase (final step of mitosis):

    - chromosomes begin to uncoil (revert back to their lose form- chromatin)

    - mitotic spindle degrade

    - nucleolus, nuclear envelope, and nuclear membrane reassemble

    - forms 2 nuclei

• Cytokinesis: the cytoplasm divides and the 2 nuclei become separated into the 2 daughter cells (the actual separation process). each daughter cell has the same number of chromosomes as the parent cell

  • In plant cells, a membrane called the cell plate forms in the center

  • In animal cells, the cell membrane pinches the cytoplasm into 2 equal parts (cleavage furrow)

11.4:

• Cell division (Mitosis) is a normal part of an organism’s:

  • growth and development

  • asexual reproduction (reproduction without gametes)

  • repair and regeneration of damaged tissues

• Meiosis: sexual reproduction that produces 4 haploid daughter cells that are not genetically identical to the diploid parent cell, with each carrying half the amount of DNA as the original parent cell

• Asexual reproduction: involves only mitosis (become clones of a single parent organism)

• Sexual reproduction: involves both mitosis and meiosis. it increases genetic diversity

• Gametes: the mature sexual reproductive cell: the egg or sperm, produced by meiosis (each parent contributes one gamete to their offspring)

  • Human gametes are haploid since they have one copy of every chromosome

• Fertilization: the process of merging 2 haploid gametes (egg and sperm fusion), producing a diploid cell

• Zygote: the very first diploid (2n) cell of a newly developing organism

• Meiosis has three main effects:

  • It reduces the chromosome number from diploid (2n) to haploid (n).

  • It ensures that each of the haploid products has a complete set of chromosomes.

  • It generates genetic diversity among the products.

• Meiosis occurs in 2 separate stages

  • Meiosis 1: reduction division – diploid cells divide into 2 haploid daughter cells 2N -->1N

  • Meiosis 2: Separates the sister chromatids. 2 haploid cells divide, producing 4 genetically different haploid daughter cells 1N -1N that will develop into egg or sperm.

• Meiosis 1 Process:

  • Interphase (same as mitosis): Chromosomes that are uncondensed replicate (in the S phase). The mother cell, which is diploid at the end of mitosis, divides into two haploid daughter cells by separating homologous chromosome pairs, halving the chromosome number in each new cell

  • Prophase 1 - recombination and crossing over: Homologous chromosomes condense and pair up closely (synapsis- adhering along their lengths), allowing for a process called "crossing over" where parts of the chromosomes exchange genetic material (DNA) between the maternal and paternal chromosome pairs, resulting in new allele combinations and genetically different chromosomes

  • Metaphase 1: The spindle attaches to chromosomes, lining up the pairs of homologous chromosomes in the middle. They are independently and randomly assigned. Independent assortment results in an enormous amount of possible genetic combinations

  • Anaphase 1: Homologous chromosomes separated to opposite ends

  • Telophase 1: Chromosomes arrive at opposite poles and uncoil. 2 new nuclear membranes form.

    Cytokinesis 1: the cytoplasm divides, forming 2 haploid daughter cells

• Meiosis 2:

  • Prophase 2: chromosomes condense, nuclear membrane breaks down, spindle forms

  • Metaphase 2: Sister chromatids line up at the middle of the cell

  • Anaphase 2: Sister chromatids are separated, chromosomes move to opposite ends

  • Telophase 2: 4 new nuclear membranes form, cytoplasm divides, 4 genetically unique haploid cells

  • Cytokinesis 2: the cytoplasm divides, resulting in 4 total haploid daughter cells

• Differences between Mitosis and Meiosis:

  • Mitosis:

    • Growth, repair & asexual reproduction

    • Occurs in somatic cells

    • 1 nuclear division

    • 2 genetically identical diploid daughter cells produced

• Meiosis:

  • Gametes for sexual reproduction

  • Occurs only in germ cells

  • 2 nuclear divisions

  • 4 genetically unique haploid gametes produced

• Nondisjunction: the failure of sister chromatids to separate in meiosis II or homologous chromosomes to separate in meiosis I

  • Aneuploidy: a condition in which one or a few chromosomes are either lacking or present in excess

  • Trisomy: has 3 chromosomes instead of the usual pair of chromosomes

    • ex: Down Syndrome (have an extra chromosome- chromosome 21)

    • ex: Klinefelter syndrome: a male with an extra X chromosome- both aneuploidy and trisomy

  • Monosomy: a cell or organism with only one copy of a chromosomes

    • ex: Turner syndrome: a female condition where there is only one X chromosome

• Translocation: a piece of a chromosome may break away and become attached to another chromosome

• Apoptosis: programmed cell death

  • Cells may no longer be needed (ex: connective tissue between fingers of a fetus)

    Old cells are prone to genetic damage that can lead to cancer (ex: epithelial cells may be exposed to radiation and toxins; they live only days or weeks)

• What error occurs that results in abnormal chromosome structures and numbers?

  • answer: no separation of chromosomes in meiosis