Inheritance of DNA 2D part 2 (Textbook) Meiosis Flashcards
homologous pair
have the same genes arranged in the same order in the DNA of the chromosome. Different versions or alleles may be present on either chromosomes
Recombination
on a molecular level what happens
invloves the precise breaking of of covalently bonded DNA backbones exchanging the ends with those of the other homologue and reforming the bonds.
as a result of recombination
Each chromosome passed on to offspring is composed of a novel miture of both maternal and paternal DNA sequences
Meiocytes
cells that are destined to divide by meiosis
interkinesis
a brief interphase that separates the two meitotic divisions
no DNA replication
Prophase 1
The replicated chromosomsomes each consist of two sister chromatids begin to fold and condense into threadlike structures in the nucleus. The chromosomes of each homologous pair then come togther and line up side by side in a zipperlike way in synapsis. When they are paired, the chromaids undergo genectic recombination.
In prophase 1 the line up of two homologous chromosomes is called a
tetrad
What holds the homologous chrommosomes pair in prophase?
synaptonemal complex
(Protein framework)
In genectic recombination..
How is this done, what happens, what holds it, what happens after done
the homologous chromosomes are held by a protein framework. Regions of the homologous chromatids exchange segments producing new combinations of alleles. This involves the breakage and rejoining of DNA molecules by enzymes. When the exchange is complete towards the end of prophase I, the synaptonemal complex disassembles and disappears.
What is exchanged in recombination
*Not just as simple to alles/genes u dummy
All the DNA sequence stretching from the site of recombination to the ends of the participating chromatids
As prophase 1 finishes,….
a spindle forms in the cytoplasm
Prometaphase I
The nuclear envelope breaks down and the spindle enters the former nuclear area. Microtubules attach to the attach to the fused kinotochore of each homologous chromosome).
In prometaphase, where are the two homologous chromosomes held tgt
at the crossover part or chiasmata
Metaphase I
Movements of the spindle microtubules align the recombined tetrads on the equatorial plane between the two spindle poles
Anaphase 1
The two chromosomes of each homologous pair seperate and move to opposite spindle poles. The movement seperate homologous pairs delievering a haploid set of chromosmes to each pole of the spindle.
Aside from genetic recombination, whats the second source of major genectic variability
The random alignment of chromosomes of maternal and paternal origin at metaphase I followed by their segreagation to opposite poles at anaphase I
Telophase I (5)
Telophase I is a brief transitory stage in which there is little to no change in the chromosomes.
The microtubules break down, the nuclear membrane reforms, and the chromosomes return to an uncondensed state.
Cytokinesis in telophase I creates halploid cells.
Interkinesis
the spindle of the first meiotic division dissaembles and microtubules reassemble into new spindles for the second division
prometaphase II
nuclear envelope breaks
spindle enters the former nuclear area
spindle attaches to the two kinetochores of each chromosomes.
Metaphase 2
+diversity arised how?
Movements of the chromosomes within the spindle bring them to rest at the metaphase plate
another chance of diversity as recombination in prophase I results in the sister chromatids being different. The orientation would determine which is going to which haploid cell.
how is meiosis 2 diff from mitosis (3)
- meiosis 2 produce reproductive cells
- there is no immediate preceding DNA replication phase
- resulting daughter cells are genetically different
Anaphase 2
sister chromatids of each chromosome seperate from eachother and move to opposite poles.
Telophase 2
chromosomes decondense to interphase state
soindles disassemble
nuclear envelope form around chromatin
cell divides
sporadic cancer
cancer not inherited
proto oncogene
normal genes that stimulate growth and cell division
Alterations that an oncogene cause can include
amplify number of of copies of the gene. A mitation in the genes promoter or other regulatory sequence that increase transcription rate or the gene is under control of a stronger promotor or enhancer.
Tumour supressor gene
What is do+ex plus what ust happen for inhibitory activity to be lost
A gene that when inactived by mutation results in a selective growth advanatage to the cell.
For ex: tumour supressor genes can encode growth inhibiting factors that inhibit cell growth and division.
Tumor supressor genes are recessive that is both alleles of a tumour suppresor gene must be inactivated for inhibitory activity fo the gene’s product to be lost un cancer cell.
