Topic 1: Chromosomes and Cellular Reproduction Flashcards
What is the n-value
The number of chromosomes of a cell
What is the c-value
Amount of DNA in an individual cell
Diploid vs haploid cells?
Diploid = cells that carry two sets of genetic information (two chromosomes)
Haploid = cells that carry one set of genetic information
n vs 2n
n= haploid
2n= diploid
What is polyploid
4n, 6n (# chromosomes)
Found in plants
In diploid cells, chromosomes occur in…
homologous pairs
Two kinds of homologous pairs
Similar but not identical (same genes in same order, different alleles of those genes)
Sister chromatids (identical alleles)
Two ways of measuring the amount of DNA within a haploid nucleus
Picograms, base pairs
Base pairs are measured in…
kb = kilo base = 100
Mb = mega = 1 million
Gb = giga = 1 billion
Number of chromosomes in a human
2n = 46
Number of genes in a human, genome size
21k genes
3 Gb genome
What is the c-value paradox
The number of genes does not indicate complexity, genome size, number of chromosomes, etc
Types of non-gene DNA?
Repetitive DNA
Centromeres
Telomeres
Two types of repetitive DNA, describe them
Moderately repetitive (150-300 bps long, found in many places in the genome, transposons)
Highly repetitive (<10 bps long, microsats)
What are centromeres
constricted region of chromosome where spindle fibers attach
Moderately repetitive DNA, tandemly repeating
What are telomeres
6 bp repeats, tandemly repeating
Repetitive sequence at the end of linear chromosomes
What is the role of telomeres
Solves end replication problem
Provide stability
The end of the chromosome that is overhanging (longer) is the
G-rich strand
What is the T-loop
G-rich strand folds over and pairs with a short stretch of DNA
What organisms are T-loops found in, what are their role?
In mammals, provide stability to the end of the chromosome
What are the phases of interphase, describe them
G1 = cell growth/development; G1/S checkpoint
S = synthesis phase (of DNA)
G2 = prepare cell for mitosis (division); G2/M checkpoint
What is the M phase?
Mitotic phase (nuclear and cell division)
What are the major checkpoints of mitosis, what do they look for?
G1/S = external conditions/DNA damage
G2/M = prevent entering into mitosis if DNA is damaged
spindle assembly = all chromosomes
properly attached to spindle apparatus
Five phases of mitosis, describe them.
Prophase = chromosomes start to condense, centrosomes start to find each other
Prometaphase = disintegration of nuclear envelope
Metaphase = chromosomes line up on metaphase plate individually; spindle-assembly checkpoint
Anaphase = sister chromatids separate
Telophase = chromosomes arrive at spindle poles, nuclear envelope re-forms
Slide 19**
Mitosis summary
What are the genetic consequences of the cell cycle
- produces two genetically identically cells
- new cells contain full complete set of chromosome
- each new cell contains half the cytoplasm of the parent cell
Meiosis produces…
haploid gametes (2n -> n)
Fertilization produces…
Fusion of two haploid cells (n -> 2n)
Broad phases of meiosis
Interphase (same as mitosis; G1, S, G2)
Meiosis I (separation of homologous chromosomes)
Meiosis II (separation of sister chromatids)
Describe meiosis 1, aka…
Reduction division
2n -> n
Metaphase plate homologous pairs line up
Different from mitosis due to change in ploidy
Describe meiosis 2, aka…
Equational division
n -> n (no change in ploidy, similar to mitosis)
Three steps of prophase 1 during meiosis 1
Synapsis: homologous pairs find each other, pair up
Tetrad: the chromosomes are now a tetrad
Crossing over: exchange of genetic material between homologous chromsomes
What is the chiasmata
Forms between homologous chromosomes (links them) before crossing over; prepares for separation/reattachment
What happens during metaphase 1 in meiosis 1
Tetrads line up on metaphase plate
What happens during anaphase 1 in meiosis 1
Separation of homologous chromosomes (segregate independently)
What is interkinesis
Stage between M1 and M2
During mitosis anaphase, what does separase do? What happens after?
Cuts all the cohesins
Microtubules then pull sister chromatids apart
What does shugoshin do
Protein that is added to cohesin to protect it from separase (only to cohesins near centromere)
Stages of Meiosis 2
Prophase II, Metaphase II, Anaphase II, Telophase II
Difference between meiosis II and mitosis
Similar, except meiosis 2 starts off with 2 haploid cells and we end up with 4 haploid cells
What happens during metaphase 2 in meiosis 2
Individual chromosomes line up at metaphase plate
What happens during anaphase 2 in meiosis 2
Separation of sister chromatids
Products of meiosis 2
4 haploid cells (gametes)
Consequences of meiosis on chromosome number
- Reduced by half
- Diploid to haploid
Newly formed cells from meiosis are…
Genetically different from one another and from the parental cell
