Lecture 3: Mitosis and Meiosis Flashcards
Mitosis and meiosis allow for
Mitosis and Meiosis allow for observation of chromosomes
Distinguish size, shape and number
What does the cell do in preparation for meiosis and mitosis
In preparation for mitosis and meiosis, each chromosome is a double structure
Composed of a pair of chromatids
Sister chromatids
Held together at the centromere
Dividing cell in mitosis in meiosis
Each new cell requires a copy
Prior to division each chromosome makes an exact copy of itself
Results in 2 chromatids
Sister chromatids
In early division stages the sister chromatids remain attached at the centromere
Once in separate nuclei they are again referred to as single chromosomes
Karyotype is
A display of a cell’s chromosomes ordered according to size
Enables detailed analysis
Cells arrested in mid-mitosis
Autosomes
Sex chromosomes
Chromosome numbers are
can vary between species
Chromosome number is constant for ‘all’ cells of a given species
#can very between species
Homologous pairs are
Chromosomes can be arranged in matching pairs
Homologous pairs
Homologous pairs have same size, shape, and functions – same genes (but perhaps different alleles)
They look the exact same
Locus is
chromosomal location of a specific gene
Gene address
Diploid is
Cell with 2 sets of chromosomes
maternal set + paternal set
2 copies of every gene
2n (n = # of chromosomes in 1 set)
Haploid is
Cell with 1 set of chromosomes
1 copy of every gene
Gametes are 1n
Mitosis is
Each cell receives the same number and type of chromosomes as were present in the parental cell
Meiosis is
Division resulting in cells with half the chromosome number of the parental cell
Sexual reproduction
Gametes are haploid (1n)
If not, the chromosome # would double every generation
Cell cycle is
Cell cycle is a series of phases that lead to cell division
The order and regulation of these phases is vital for the process of cell division
Phases of the cell cycle
G1
S
G2
M
Collectively the first 3 phrases are called interphase
G1 step of the cell cycle is
the first gap phase
Cell growth
S of the cell cycle is
synthesis phase
DNA replicated (single to duplicated chromosomes)
G2 part of the cell cycle is
the second gap phase
Protein synthesis for division
M in the cycle cycle is
mitosis and cytokinesis
Mitotic cell division is
Cell divides to produce 2 new cells that are genetically identical to the original cell
Involves mitosis and cytokinesis
Mitosis – division of the nucleus into 2 nuclei
Cytokinesis – division of the cytoplasm to produce 2 daughter cells
Biological significance of mitosis
Enables the growth of an organism
From unicellular zygote to multicellular organism
Repair of damaged tissues
Normal cellular replacement (skin, gut lining)
Asexual reproduction reproduction
New organism produced from one parent
Stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Prophase of mitosis
Duplicated chromosomes condense
Nuclear membrane dissociates
Mitotic spindle begins to form
Metaphase of mitosis
Duplicated chromosomes are aligned along the metaphase plate (equator) in a single row
Metaphase plate is halfway between the 2 poles
Spindle microtubules attach to the centromeres of the duplicated chromosomes
Anaphase of mitosis
Sorting process occurs
Connection between sister chromatids is broken
Single chromosomes separate
Telophase in mitosis
Single chromosomes have reached poles
Nuclear membranes reform to produce 2 separate nuclei
Chromosomes decondense
Cytokinesis in mitosis is
Division of cytoplasm to produce distinct daughter cells
Involves cleavage area
Constricts like a drawstring to separate cells
At end of cytokinesis the daughter cells are in interphase
Meiosis is the proccess in and results in
Process by which haploid cells are produced from a cell that was originally diploid
A type of nuclear division involved in gamete production
Involves one round of chromosome replication and two successive rounds of nuclear division
Results in 4 haploid daughter cells
Biological significance of meiosis
Ensures consistent chromosome number from generation to generation
Ensures variability among offspring due to new combinations of alleles
independent of chromosomes at metaphase I
Swapping of pieces of homologous chromosomes
New combinations of alleles on the same chromosome
Random fertilization of gametes
Cell cycle differentiats of meisosis is
Meiosis begins after a cell has progressed through G1, S and G2
Two rounds of division are called meiosis I and meiosis II
In meiosis I homologous chromosomes are separated – halves the number of chromosomes
In meiosis II sister chromatids are separated
Synapses and crossing over in meiosis
Synapsis and crossing over are 2 key events that occur in meiosis but not mitosis
Synapsis is the process of forming a bivalent
Bivalent is formed when homologous chromosomes become very closely associated
Crossing over is
Involves a physical, reciprocal exchange of DNA between homologous non-sister chromatids
Allows for increased variation in genetic information
Chiasma = connection at a crossover site of 2 chromosomes
Stages of meiosis
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase I in meiosis is
Chromosomes condense
Meiotic spindle begins to form
Nuclear membrane dissociates
Homologous chromosomes synapse and form bivalents
Crossing over occurs
Metaphase I in meiosis
Bivalents attach to microtubules of spindle apparatus
Bivalents align at Metaphase I plate
Anaphase I in meiosis
Homologous chromosomes separate and move to opposite poles
Sister chromatids are still attached at centromere
Telophase I in meiosis
Duplicated chromosomes arrive at the poles
Nuclear membranes form
Chromosomes begin to decondense
Cytokinesis I occurs
2 cells are produced, each with the haploid number of duplicated chromosomes
Meiosis II is
Meiosis II is similar to mitosis
However, there is no “S” phase before meiosis II begins
The chromatids of each chromosome may no longer be identical because of crossing over
Steps in meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Difference between meiosis and mitosis chromosome behaviour
Mitosis: Homologous chromosomes independent
Meiosis: Homologous chromosomes pair (synapse) forming bivalents until anaphase I
Difference between meiosis and mitosis chromosome numbers
Mitosis- identical daughter cells
Meiosis- daughter cells haploid
Difference between meiosis and mitosis genetic identity of progeny
Mitosis: identical daughter cells
Meiosis: daughter cells have new assortment of parental chromosomes
Meiosis: chromatids are not identical
Crossing over
