Law: Cellular Reproduction

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Characteristics of Prokaryotic and Eukaryotic Cells, Binary Fission, Stages of Cell Division, Mitosis, Meiosis in males and females

General Characteristics of Prokaryotic Cells

1. contains a simple structure
2. has naked DNA in Nucleoid - no membrane surrounding DNA
3. unicellular
4. ie) Bacteria, Archaea

Binary Fission

1. reproductive process of prokaryotic cells
2. circular DNA chromosome attaches to cell wall
3. DNA replication begins at origin of replication
4. chromosomes separate
5. cells separate

General Characteristics of Eukaryotic Cells

1. cells can be unicellular or multicellular
2. contains a complex structure
3. DNA is located in nucleus which is physically separated from cell in a membrane
4. contains many organelles like mitochondria, ER, Golgi Apparatus

Somatic Cells

1. all cells in organisms except the reproductive cells
2. cells undergo mitosis

Gametes

1. Reproductive cells
2. Sperm - male
3. Egg - female
4. cells undergo meiosis

Phases of the Cell Cycle

1. G1
2. S
3. G2
4. M

G1 Phase

1. phase that follows mitosis/meiosis
2. most cell growth occurs in this stage
3. Toward the end of this phase cells may choose to Divide - G1S Checkpoint

S Phase

DNA replicates

G2 Phase

1. formation of microtubule subunits
2. Mitochondria replicate (for energy purposes and it's own DNA replication)

M Phase

1. either Mitosis or Meiosis
2. Create Spindle by joining mictrobule

G1S Check Point/ Restriction Point

1. cells decides whether to divide or stay in G₀ Phase
2. 3 options that can occur

3 Options at G1S Check Point

1. Apoptosis - programmed cell death
2. DNA repair
3. opt out of cell cycle - stay out of replication cycle and return when needed or wanted (G₀ Phase)

Autosomes

1. Chromosomes other than the sex chromosomes
2. aka homologous pairs
3. In Humans, 1-22

Interphase

1. period of time in cell cycle between mitotic divisions
2. includes G1, S, G2

Chromatin

1. Occurs in Interphase and DNA replication during S phase
2. contains DNA and Histone Proteins
3. beads on a string model

Nucleosome

DNA wrapped around a histone protein

Chromosomes

1. super coiled state of chromatin
2. only visible in M Phase of Cell Cycle (mitosis and meiosis)
3. specific linear structures
4. chromosomes exist in pairs (paternal and maternal)

# of Chromosomes in Humans

1. 46 chromosomes
2. 23 Pairs

Diploid Cells

1. 2n
2. chromosomes exist as homologous pairs
3. only in somatic cells

Haploid Cells

1. 1n
2. member of the pair is present
3. occurs in gametes - sperm and ova

Single Chromosomes vs Double Chromosomes

1. Single Chromosomes have not replicated yet
2. Double Chromosomes have replicated DNA, identical sister chromatin are held together at the centromere

Chromatids

1. one of the strands of a duplicated chromosome, joined together by a single centromere to its sister chromatid
2. sister chromatids are joined together by centromere

Mitosis

1. nuclear division followed by cytokinesis
2. occurs in somatic cells

Stages of Mitosis

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Prophase

1. nuclear envelope and nucleolus breaks down
2. chromatine condense to form chromosomes
3. spindle fibers forms - centromeres and microtubules
4. centrioles divide and migrate to opposite poles
5. sister chromatids at kinetochore attach to fibers from different poles
6. spindle fibers pull chromosomes

Metaphase

1. chromosomes move to the center of the spindle
2. align at equatorial plate or metaphase plate

Anaphase

1.chromatids separate at centromere forming single chromosomes
2. single chromosomes move to opposite poles being pulled by spindle fibers
3. poles move father apart and cell elongates

Telophase

1. complete set of chromosomes at each pole - 46 chromosomes
2. spindle fibers detach and spindle fibers break down
3. nuclear envelope and nucleolus reforms
4. cell continues to elongate

Cytokinesis

1. cytoplasmic division of cell
2. indentation of cell membrane at center of old spindle
3. microfilaments (actin) pinch cell inward forming a cleavage furrow
4. cell divides to form 2 new daughter cells

Meisosis

1. process of cell division in which one cycle of chromosome replication is followed by 2 successive cells divisions.
2. forms 4 haploid cells
3. only occurs in sex cells
4. daughter cells are not genetically identical to either parent cell or each other

Stages of Meiosis

1. Meiosis I
2. Meiosis II

Prophase I

1. nuclear envelope and nucleolus disappears
2. spindle fibers form
3. chromatin condense to chromosomes
4. spindle fibers attach to one chromosome (on one side)of each homologous pair
5. spindle fibers pull chromosomes toward middle
6. synapsis occurs - (46 chromosomes, 23 pairs)
7. Recombination or crossing over occurs

Synapsis

1. homologous chromosomes find each other and pair up
2. point by point intimate association

Recombination or Crossing Over

1. breaking and rejoining of maternal and paternal homologous chromosomes

Chiasma

points at which chromosomes cross over

Metaphase I

1. homologous pairs align at metaphase plate
2. one member of each pair faces opposite pole
3. random orientation of pairs

Anaphase I

1. chromosome pairs separate and move to opposite poles
2. no centromere splitting occurs
3. chromosomes are still doubled
4. poles are moving further apart

Telophase I

1. complete haploid set of chromosomes are at opposite poles
2. spindle fibers detach and spindle breaks down
3. cytokinesis follows resulting in 2 haploid cells
4. 46 chromosomes or 23 pairs in each cell

Period After Cytokinesis of Meiosis I

1. cells may or may not go back into interphase
2. depends on cell type, sex, species
3. nuclear membrane and nucleolus reform
4. chromosomes become chromatin

Prophase II

1. 2 haploid cells enter into this phase, chromosomes are still double
2. chromatin condenses
3. nuclear envelope and nucleolus disappear
4. spindle fibers form and attach at kinetochore of each sister chromatid
5. spindle fibers pull chromosomes

Metaphase II

1. unpaired chromosomes of haploid cells align at metaphase plate

Anaphase II

1. centromeres split and single chromosomes move to opposite poles

Telophase II

1. spindle fibers detach and dissolve
2. nuclear envelope and nucleolus reforms
3. cell elongates
4. cytokinesis follows to produce 4 cells each containing 23 chromosomes/chromatids

Spermatogenesis

1. occurs in the seminiferous tubes of the testes
2. begins as a spermatogonium and divide via mitosis starting in puberty and continues throughout life
3. spermatogonia produce primary spermatocytes that under meiosis I
4. After Telophase I, primary spermatocytes produce 2° spermatocytes
5. 2° spermatocytes will undergo meiosis II to form spermatids that will mature to become sperms
6. Carries 22 autosomes and either 1 X or 1 Y chromosome
7. single ejaculate contain 200-300 million sperm

Oogenesis

1. occurs in the follicles of the ovaries
2. Oogonia are formed early in embryonic development
3. All oogonia become 1°oocytes before birth
4. 1° oocytes stop at prophase I until puberty
5. at puberty, 1° will finish meiosis I in the menstrual cycle
6.forms 2°oocyte and a polar body (removed) which will be ovulated or 2°oocyte will become fertilized
7. a fertilized 2° oocyte will undergo meiosis II to form an ovum and 3 polar bodies (removed)
8. fertilized ovum and sperm fuse to form a diploid zygote

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