Unit 4 - Cell Cycle, Mitosis, Meiosis Flashcards
Gametes
- 23 different chromosomes (no pairs)
- haploid
-ova (eggs) and sperm
Zygotes
Fertilized egg
- Egg + sperm
Somatic cells
- all body cells except for ones undergoing/resulting from meiosis
- muscle, nerve
How many chromosomes are in somatic cells
- 46 = diploid
- 23 homologous pairs (one form each parent)
Homologous chromosomes
- found in somatic cells
- a chromosome pair (one from each parent) that are highly similar in length, centromere position, and have genes for the same trait (eye colour0 in the same location (locus)
- may have alleles that code for proteins that produce alternate versions of that trait
Gene
- unit of heredity
- region of DNA which contains information for synthesis of a protein
Alleles
- different versions of a gene
- ex. Blue eyes (chromosome from one parent), brown eyes (chromosome from second parent)
Diploid cells
Contain 23 chromosomes from an ovum paired with 23 chromosomes from a sperm = 46 chromosomes
How are chromosomes numbered
- 1 to 23
- 1 to 22 = autosomal chromosomes (autosomes)
- 23 = sex chromosome
Autosomal chromosomes
- contain genes for somatic characteristics
- ex. Hair colour, eye colour, height
- each autosomal chromosome pair is not identical, but equivalent = homologous chromosomes
Sex chromosomes
- contain genes that determine biological sex
- XX = female
- XY = male
- X or Y from sperm
- X from ovum
Mitosis
- cell cycle for growth and repair of tissues
- diploid somatic cell to 2 genetically indentical somatic diploid cells
- 2 stages
1. Interphase
2. Mitotic/cell division phase
Interphase (mitosis)
- G1, S and G2
- cells spend most of their lives here
- chromosomes are present as long thread-like chromatin strands
- normal cellular metabolic activities occurring (ex. protein synthesis)
- must have 2 of everything in order to divide (everything must duplicate)
G1 of interphase
- growth and metabolism
- Centrosome replication begins
G0 of interphase
- cells that do not divide again once mature (stay in G1)
- nerve and some muscle cells
S phase of interphase
- chromosomes replicate, but are still present as long thread-like chromatin strands ( not individually visible)
- ALWAYS occurs before cell division
- Replicates are called sister chromatids
Sister chromatids during S phase
- attached rot each other at an area of DNA called the centromere
- Kinetochore form on each centromere
Kinetochore
- site of attachment of spindle microtubules
G2 phase
- Growth and metabolism
- production of enzymes and other proteins needed for cell division
- Centrosomes replication is completed
What does the mitotic phase involve
- Mitosis
- Cytokinesis
Mitosis
Is the division of nuclear material (chromosomes)
4 phases of mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
Cytokinesis
Is the division of cytoplasm
What happens when the mitotic phase ends
- mitosis and cytokinesis are complete
- resulting diploid cells to into interphase (G1)
- cycle starts over
What happens to chromosomes during mitosis
- condense (thicken and coil)
- become individually visible
What happens to the nucleoli during prophase (mitosis)
They disappear
What happens to the nuclear envelope during prophase (mitosis)
It breaks up
Centrosomes during prophase (mitosis)
Move to opposite ends (poles) of the cell
Spindle microtubules during prophase (mitosis)
Grow out of Centrosomes and attach to Kinetochore proteins of each sister chromatid, forming the spindle apparatus
- spindle begins to move chromosomes towards cell equator
Metaphase (mitosis)
46 replicated chromosomes line up on cell equator
What happens during anaphase (mitosis)
- spindle microtubules shorten and pull the Kinetochores away from each other
- causes separation of centromeres
- results in separation of the sister chromatids into 92 individual chromosomes
How many chromosomes migrate to each pole during anaphase (mitosis)
46
When does cytokinesis being in mitosis
At the end of anaphase
What happens to chromosomes during telophase (mitosis)
They uncoil into long thread-like strands of chromatin
What reappears during telophase (mitosis)
- nucleoli
- nuclear envelope
During what phase of mitosis do the spindles disassemble
Telophase
During what phase of mitosis does cytokinesis end
At the end of telophase (after telophase is complete)
What does meiosis produce
Gametes (ovum and sperm)
- 1 cell (diploid) produces 4 genetically unique gametes (each haploid)
Stages of meiosis
- Interphase
- Meiosis I
- Meiosis II
Interphase of meiosis
Is the same as interphase of mitosis
Meiosis I
- reduction division in which chromosome number changes from diploid to haploid)
- stages:
1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase I
5. Cytokinesis
Prophase I
- homologous chromosomes attach together to form tetrads (4 chromatids in a row)
Metaphase I
- 23 tetrads line up along cell equator
What happens to tetrads during anaphase I
They separate and migrate to opposite poles
- one homologous chromosome (with 2 sister chromatids) goes to each pole
Do sister chromatids separate during anaphase I
NO!!!
Telophase I
- identical steps to telophase of mitosis but with 23 replicated chromosomes instead of 46
After meiosis I and cytokinesis
- each new cell has 23 different chromosomes (1/2 the number of- haploid)
After meiosis I and cytokinesis do the cells have homologous chromosomes?
NO!!!
What does each cell have after meiosis I and cytokinesis
A single copy of each autosomal chromosome and a single sex chromosome
Meiosis II
Is the same as mitosis except it starts with 23 chromosomes instead of 46
metaphase II
23 replicated chromosomes line up at equator
Anaphase II
Sister chromatids split up and 23 chromosomes migrate to each pole
Cytokinesis after meiosis II
Is the same as for mitosis/meiosis I
- begins in anaphase/anaphase I/anaphase II
- continues through telophase/telophase I/telophase II
Why does meiosis occur
- we need to turn diploid germ cells into haploid gametes (ova/sperm)
- create zygotes
Zygote
46 chromosome cell formed from a 23 chromosome haploid sperm cell combined with a 23 chromosome haploid ovum
