Chapter 11 Flashcards

Chromatin

the loose form of DNA decondensed- associated with histone proteins

Chromosome

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 (in humans, that’s 46 chromosomes total, 23 from each parent)

• n= number of chromosomes

Haploid

1n (1 copy/set) of each chromosome (23 chromosomes total in humans)

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 and meiosis

Somatic cells

all the cells of the body that are not specialized for reproduction (contain 2 sets of chromosomes, one set 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

How do prokaryotes divide?

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

1. DNA replication: 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

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

3. 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 (clones)

• FtsZ is in prokaryotes only!

What are the phases that a eukaryotic cell passes to produce daughter cells by cell division?

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 each into 2 sister chromatids)

G2 phase

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

G0 phase

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 (mitosis)

• 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 (mitosis)

mitotic spindles align chromosomes in the middle of the cell in a line

Anaphase (mitosis)

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 (mitosis) + in plants and animals

the cytoplasm divides and the 2 nuclei become separated into the 2 daughter cells (the actual separation process). each daughter cell is genetically identical to the parent cell (clones)

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

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

Image of Mitosis Process

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 cells, with each carrying half the amount of DNA as the original parent cells

• 1 diploid parent (results from mitosis) → 4 haploid daughter cells

• Meiosis reduces the chromosome number by half, transitioning from a diploid cell (containing two sets of chromosomes) to a haploid cell (containing one set of chromosomes).

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- egg or sperm)

• 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) → aka by half

• 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:

• 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 Process:

• 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

(function, which cells they occur in, how many nuclear divisons occur in each, what types of cells do they produce and how much?)

• 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 (which type of error is it + give its definition + ex.)

A type of nondisjunction

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

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

Trisomy (which type of error is it + give its definition + ex.)

A type of nondisjunction

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 (which type of error is it + give its definition + ex.)

A type of nondisjunction

a cell or organism with only one chromosome instead of the usual pair

ex: Turner syndrome: a female condition where there is only one X chromosome (both monosomy and aneuploidy)

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?

no separation of chromosomes in meiosis