Lesson 9 - Cell Division and Genetics (1-42) Flashcards
Genes
genes code for a specific trait (units of heredity). Segements of DNA
Many genes on one chromosome, a specific locus point on the chromosome
Centresome (middle) and sister chromatids on chromosome
Human chromosomes
Somatic cell
46 chromosomes (diploid), two sets of 23, one from each parent
Gametes (sperm and egg cells)
haploids, 1 set of 23 chromosomes, result of meiosis
Cell division
Process in which cells reproduce themselves using cell cycle
Some cells divide repeatedly, use stem cells (skin, blood and cheek cells)
Some cells stay alive but don’t divide, active and can repair (muscle and nerve) called cell G0 cells that stay in G1
Other cells divide infrequently (bone)
Chromosomes
Replicated in S phase, to prepare for cell division. DNA is replicated and chromosomes condense
Each duplicated chromosome has two sister chromatids (92 total)
Cell divison by Mitosis
for eukaryotic cells
Interphase
-chromosomes dulipcate
-cells parts are made
-G1 S and G2 phase
mitosis
- chromatids split
-2 equal cells
-Prophase, Prometaphase, Metaphase, Anaphase, Telophase and Cytokinesis
92 chromatid
46 chromosomes
23 sets
Interphase
G1 phase - cell grows, multiple organelles and is active
S phase - cell synthesizes DNA
G2 phase- cell grows, centrioles replicate
Prophase
-Chromatin condenses into chromosomes
- Nuclear wall degenerates
-centrosomes starts to move apart (opposite ends)
Prometaphase
Intermediate step
- Nuclear envelope disappears
-spindles from chromatids to chromosomes
- Kinetochore proteins appear
Metaphase
-centromeres of chromosomes line up at the metaphase plate (midline)
-Mitotic spindles start to form
Anaphase “out of here”
-centromeres of chromosomes split
-sister chromatids move toward opposite poles of the cell
Kinetochore microtubules
Part of anaphase
Kinetochore microtubules move chromatids toward opposite ends of the cell
Nonkinetechore microtubules
Overlap and push against each other, elongating the cell
Telophase
-Mitotic spindle dissolve
-Chromosomes become chromatin
-New nuclear membrane forms
-reverse of prophase
Cytokinesis
Splitting of the cell
-divison of cytoplasm
-Occurs with telophase
- Cleavage furrow pinches cell in two (actin-myosin drawstring)
-After cytokinesis, new cells enter interphase
The Cell Cycle Control System
Events of the cell cycle are directed by a
control system
-Specific checkpoints to avoid uncesscary division
G1 checkpoint- passed if nutrient sufficient, cell size big enough and DNA undamaged
G2 checkpoint (before mitosis)
- two regulatory proteins involved in cell cycle
-Cyclins and cyclin dependant kinases (cdks)
- Cyclins and cyclin dependant form MPF , a maturing promotor which triggers mitosis
External factors
-External cell factors can also trigger cell division
Eg. Growth factor
Density-dependent Inhibition
- Crowded cells stop dividing
Anchorage dependence
- Cells must be attached to substratum to divide
Cancer cells
No density-dependent inhibition
-dont care and keep dividing, overrides checkpoint
- form tumours
Apoptosis vs Necrosis (cell death)
Apoptosis - “Programmed cell death”
Protective process
* E.g. with cell dysfunction
* May protect us from cancers
Necrosis - Cell death triggered by
inflammation
Meiosis
- Sexual reproduction
- Produces a haploid set of chromosomes
Eg. Eggs and sperm - Chromosomes replicate once
2 cell divisions (meiosis I and meiosis II)
Meiosis I Meiosis II
Meiosis I- Reduces chromosomes from
diploid to haploid
Meiosis II - Produces four
haploid daughter cells
Crossing over important
Exchanging DNA is prophase I
Increases Genetic variability
Produces chromosomes that carry genes from two different parents
Interphase and Meiosis I
Interphase - chromosomes dulipcate
Prophase I - 6 total chromosomes, crossing over
Metaphase I - form at midline
Anaphase I - spitting chromosomes to appositive polres
Telophase and Cytokinesis I and meiosis II
Telophase I and Cytokinesis I - straight to prophase after split
Prophase II - rid of nuclear membrane
Metaphase II - already haploid, midline
Anaphase II - split to opposite poles
Telophase II and Cytokinesis II - back to chromatid, three unique crossovers
Mitosis vs Meiosis
prophase:
while both partake in chromosome replication. Meiosis has the crossing over leading to genetic variability
Metaphase:
In mitosis chromosomes (all 6) are lined up singularly the at metaplate while in meiosis they lined up in parts.
Anaphase and telophase:
In mitosis sister chromatids separate during anaphase to create daughter cells. While in meiosis in anaphase I, homologues separate and sister chromatids remain together creating haploids (telophase I). In Meosis II 4 daughter cells are created and sister chromatids separate in anaphase II.
Independent Assortment
Each pair of chromosomes sort its maternal and parental homologues into daughter cells independently of the other pairs
Random assorting
Genetic variability
So many combinations, 64 trillion
Independent assortment, random fertilization and crossing over
Meiosis malfunction
Abnormal chromosome count
-the failure of homologous pairs to separate during meiosis I
- the failure of sister chromatids to separate during meiosis II
Leads to birth defects
most common is Down syndrome by trisomy 21 (extra copy)
