Ch.1 Mitosis and Meiosis Flashcards
Mitosis
Partitions chromosomes into dividing cells
Creates identical daughter cells
No genetic variation
Meiosis
Creates haploid gametes
Creates non-identical daughter cells
Genetic variation
All organisms are made of what?
Cells- one of the properties of living organisms
Multicellular organisms
consist of more than one cell
Unicellular organisms
consist of only one cell
Living things can only arise from?
Can only arise from living things
The cellular environment
Cytoplasm-the inside of the cell; water; hydrophilic and hydrophobic molecules; carbohydrates; lipids; proteins including enzymes; membrane- made of lipids and proteins; organelles
Prokaryotic
(bacteria, archaea) no cell nucleus
Eukaryotic
(protists, plants, fungi, animals) cell nucleus
In both unicellular and multicellular organisms, prokaryotic and eukaryotic cells, where is the genetic material located?
It is organized into chromosomes
All cells share some common features, what are they?
DNA organized in chromosomes; plasma membrane; ribosomes
Nucleus
Found in eukaryotes
Membrane bound
Houses genetic material (DNA)
Nucleolus- where ribosomal RNA (rRNA) is synthesized
Nucleoid
Found in Bacteria and Archaea (prokaryotes)
Nucleoid region
NOT membrane bound
Area of DNA
Chromosomes
Double-stranded DNA with associated proteins and sometimes RNA
Unit of DNA molecule which is passes on to the next generation
What kind of chromosome is in prokaryotic cells?
Contains 1 circular chromosome plus smaller plasmids (ring shaped DNA molecules)
What kind of chromosome is in eukaryotic cells?
Most eukaryotic cells contain several large linear chromosomes
Chromatin
association of double stranded DNA and proteins
Chromosomes are the condensed form of what?
Chromatin. (Discrete units)
Why does DNA have to be organized in discrete unites before the cell can divide?
It makes it easier to distribute DNA molecules evenly to daughter cells
Order of condensing
Double helix DNA, “Beads on a string” DNA wound on nucleosomes, chromatin fiber, chromosomes
How is chromosome shape determined?
Location of centromere determines appearance of chromosome
Metacentric chromosome
centromere is in the middle
Submetacentric chromosome
centromere is in between middle and end
Acrocentric chromosome
centromere is close to the end
Telocentric chromosome
centromere is at the end
Karyogram
chromosomes sorted into homologous pairs, organized and labeled by size
Metaphase chromosomes
chromosomes are fully condensed into X shape
How many chromosomes in a human?
22 pairs of autosomes and 1 pair of sex chromosomes
XY- male
XX- female
Diploid cells (2n)
have 2 sets of homologous chromosomes (maternal/paternal)
Human 2n=46
Haploid cells (n)
have 1 set of chromosomes
human n=23
Somatic cells
nonreproductive cells in the body of a eukaryote
Are somatic cells diploid or haploid?
Diploid (2n)
Sex cells (gametes)
reproductive cells: sperm and egg cells produced by diploid cells of the germ line
Germ line
tissue that produces reproductive cells
Are sex cells diploid or haploid?
Haploid (n)
Human sexual life cycle
Germ line (reproductive tissue) - ovary and testis
Meiosis- produces sex cells (n state)
Egg and sperm - each is in the haploid state (one set of chromosomes)
Fertilization results in zygote (2n)- 1st diploid state of human
Mitosis and development into human - body is 2n
Homologous chromosomes
the 2 chromosomes in a pair: one maternally, one paternally derived
Are homologous chromosomes identical?
They are identical in size and shape. They contain the same information (genes) but in variants (alleles)
Sister chromatids
arms of the chromosome which consist of identical copies of DNA
Eye color on homologous chromosomes
Eye color gene is located at a specific site (locus). Both chromosomes in a homologous pair have the same genes at the same loci. One chromosome carries the allele for brown eyes (B) at the eye color gene locus, the other chromosome carries the blue eye allele (b)
Eye color on sister chromatids
the sister chromatids within one chromosome are identical. They both have BB or both have bb
MTOCs
microtubule organizing center - differentiated into centrosomes which each contain 2 centrioles
Where do microtubules start to form?
From the centrosomes
Microtubules
protein fibers, attach to the centrosome of the chromosomes and move them
What do the microtubules make up?
The mitotic spindle (spindle apparatus)
How do microtubules move the chromosomes?
Protein fibers start to degrade and get shorter which causes movement of the chromosomes
Mitosis (2n -> 2n)
cell division that creates 2 daughter cells identical to the parent cell (bc the sister chromatids get separated and divided onto the daughter cells)
Meiosis (2n -> n)
Cell division that creates sperm and egg cells. The sperm cells and the egg cells created are NOT identical to each other (bc the homologous chromosomes get separated and divided)
Ovaries/testes are diploid -> sperm and egg are haploi
Mitosis - when eukaryotic cells divide, how do that distribute their genetic material?
They distribute their genetic material equally and exactly to their offspring.
Ex of mitosis: tissue renewel
all of your skin cells are identical clones: they carry identical DNA molecules
Mitosis steps
Interphase Prophase Metaphase Anaphase Telophase
Mitosis step 1 (interphase to prophase)
Chromosomes duplicate to produce sister chromatids
Mitosis step 2 (prophase)
Duplicated chromosomes condense
Mitosis step 3 (metaphase)
Duplicated chromosomes migrate to the equatorial plane of the cell and nuclear membranes breaks down
Mitosis step 4 (anaphase)
Sister chromatids of each duplicated chromosome move to opposite poles of the cell (microtubule fibers in contact w/centromere)
Mitosis step 5 (anaphase to telophase)
chromosomes decondense and new nuclear membranes form
Mitosis step 6 (cytokinesis)
membrane forms between daughter cells
What forms during cytokinesis in animal cells?
Cleavage furrow
What forms during cytokinesis in plant cells?
Formation of a cell plate
What gets separated during mitosis?
Sister chromatids (which contain identical DNA molecules)
Do all cells within one organism carry identical DNA molecules?
Yes - but they can be specialized in their form and function (RBCs, skin cells, neurons)
What are the 2 phases of the cell cycle?
Interphase and mitosis
Steps in interphase
G1, G0 (non dividing) S phase, G2
What happens in the S phase of the cell cycle?
DNA synthesis: sister chromatid form
What happens during the G phases of the cell cycle?
GAP - DNA molecules are not active. Synthesis of proteins required for mitosis.
How often and how fast cell divides depends on what?
The type of cell
The cell cycle passes several checkpoints and gets signal to proceed.
TRUE
What happens during cancer?
Cells divide uncontrolled and tumor grows
Reduction division
2n -> n (meiosis
Family and meiosis
Family members look similar to each other. Family members are not genetic identical clones
What type of cells does meiosis produce?
haploid gametes (reduction division)
What type of cells can undergo meiosis?
Only diploid cells
What are haploid cells (gametes) produced by in meiosis?
They are produced by the diploid cells of the germ line (tissue in ovaries and testes)
Are somatic cells diploid or haploid?
Diploid (2n) - one set of chromosomes from mom and one set of chromosomes from dad
Are gametes diploid or haploid?
Haploid (n) - one set of chromosomes
Meiosis interphase overview
Pair of homologous chromosomes in diploid parent cell -> Chromosomes duplicate -> end with diploid cell with duplicated chromosomes
Meiosis 1 overview
Homologous chromosomes separate. End with 2 haploid cells with duplicated chromosomes
Meiosis 2 overview
Sister chromatids separate. End with 4 haploid cells with unduplicated chromosomes
Meiosis - Prophase 1
5 substages: leptonema, zygonema, pachynema, diplonema, diakinesis. End - centromeres are present on the equatorial plate
Leptonema
chromosomes condense, visible as long thin threads
Zygonema
synapsis (pairing) of each pair of homologous chromosomes (bivalent) (chromosomes have 1 chromatid)
Pachynema
more condensation, splits into 2 sister chromatids (tetrads) crossing over
Tetrads- 4 chromosomes each pair
Diplonema
within tetrads, sister chromatids separate. Chiasma-where chromatids are still intertwined
Diakinesis
Nucleus and envelope break down; centromeres attach to spindle fibers
Chiasmata (chiasma)
Homologous chromosomes exchange pieces with each other (non-sister chromatids). The inner non sister chromatids exchange pieces.
Resulting chromosomes of crossing over
still homologous, but they are now mixtures of maternal and paternal pieces - recombinant chromatids
Recombinant chromatids
sister chromatids, not identical anymore
Meiosis - Metaphase 1
Paired chromosomes align on the equatorial plane. Paired chromosomes are oriented toward opposite poles. Terminalisation
Terminalisation
chiasmata move toward telomeres (end of the chromosome arms)
Meiosis - Anaphase 1
Homologous chromosomes disjoin and move to opposite poles of the cell. Chromosome disjunction. Separated homologues move toward opposite poles
Chromosome disjunction
separation of paired chromosomes
Meiosis - Telophase 1
Chromosomes reach the new poles; nuclei forms Spindle apparatus disassembled Daughter cells separated by membranes Chromosomes decondense Each chromosome still has 2 chromatids
Meiosis II is similar to what?
Mitosis
Meiosis - Prophase II
(Chromosomes, each consisting of 2 sister chromatids, condense and become attach to spindle fibers)
Chromosomes condense
Chromosomes attach to a new spindle apparatus
Chromatids are attached to spindle fibers from opposite poles
Meiosis - Metaphase II
Chromosomes align at equatorial plane in each cell
Meiosis - Anaphase II
(Sister chromatids disjoin and move to opposite poles in each cell)
Centromeres split
Chromatid disjunction
Chromatid disjunction
chromatids move toward opposite poles
Meiosis - Telophase II
(Chromosomes decondense and new nuclei begin to form)
Separated chromatids gather at poles; daughter nuclei form
Each chromatid is now called a chromosome
Each daughter nucleus contains a haploid set of chromosomes
Cytokinesis
The haploid daughter cells are separated by cytoplasmic membranes
Meiosis results in
4 haploid daughter cells. Not identical to mother cell and not identical to each other
Gametogenesis
process of the formation of gametes (occurs in the gonads)
Oogenesis definition
Formation of eggs. Takes place in the ovaries
Spermatogenesis definition
Formation of sperm. Takes place in the testis
Spermatogenesis overview
Spermatogonia (undifferentiated diploid cells) produce haploid cells through meiosis
Haploid cells differentiate into mature gametes
All of the 4 cells develop into sperm cells
Spermatogenesis detailed
Spermatogonia (2n) -> primary spermatocyte (undergo meiosis 1) - secondary spermatocyte (n). Eventually form 4 spermatids that mature into 4 sperm cells
Oogenesis overview
oogonia (undifferentiated diploid cells) produce haploid cells through meiosis
Haploid cells differentiate into mature gametes
Only 1 of the 4 cells becomes an egg (ovum), other 3 degenerate (polar bodies)
Oogenesis detailed
Oogonium (2n) -> primary oocyte (undergo meiosis 1) -> divides uneven to produce a polar body and a secondary oocyte (undergo meiosis 2). Eventually produces 1 haploid egg cell and 3 haploid polar bodies
What 3 mechanisms contribute to genetic variation?
Crossing over, independent assortment of chromosomes, random fertilization
What is responsible for most of the variation that arises in each generation?
Behavior of chromosomes during meiosis and fertilization
How do homologous pairs of chromosomes orient at metaphase 1 of meiosis?
Randomly
Independent assortment
Each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs. Partners in a homologous pair (and chromatids) end up randomly in the daughter cells
Number of combinations in independent assortment
2^n where n is the haploid number. For humans (n=23) there are more than 8 million (2^23) possible combos of chromosomes
Why does random fertilization add to genetic variation?
Because and sperm can fuse with any egg cell
How many combinations can the fusion of 2 gametes produce?
8.4 million chromosome combinations from independent assortment. Women and men produce this many so 70 trillion diploid combos possible. Crossing over adds even more variation
Each zygote has a unique genetic identity
TRUE
- Living organisms are are categorized into 2 major groups based on the presence or absence of a nucleus. What group is defined by the presence of a nucleus?
Eukaryotic organism
2.The diploid chromosome number of an organism is usually represented as 2n. Humans have a diploid chromosome number of 46. What would be the expected haploid number?
23
- What occurs in meiosis but not in mitosis?
synapsis of chromosomes
- What significant mechanism happens in S phase of the cell cycle?
DNA synthesis
- Fly has a haploid chromosome number of 6. How many chromatids should be present in a diploid, somatic, metaphase cell?
24
- The centromere of a chromosome separates during?
Anaphase
- If a typical somatic cell has has 64 chromosomes, how many chromosomes are expected in each gamete of that organsism?
32
- What is true about the second meiotic division?
Sister chromatids are pulling apart
- During meiosis chromosome number reduction takes place in?
Anaphase 1
- What happens during early metaphase of of mitosis?
Chromosomes align at metaphase plate
