Week 11 Meiosis and cell junctions Flashcards
What are the two stages of Meiosis?
Meiosis 1 and Meiosis 2
What are the 4 phases of Meiosis 1?
Prophase 1, Metaphase 1, Anaphase 1, and Telophase 1
What happens during Prophase 1?
- Chromosomes condense
- The spindle forms
- Nuclear envelope breaks down
- Homologous chromosomes join together and join at regions called the Chiasmata where regions of the homologous chromosomes are swapped
What is crossing over in meiosis?
Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis
What is the chiasmata?
In genetics, a chiasma is the point of contact, the physical link, between two chromatids belonging to homologous chromosomes.
What happens in Metaphase 1?
- Chromosomes attatch to kinetochores
- Chromosomes allign in the middle of the cell
- Homologous chromosomes align together
What happens in Anaphase 1?
- The chromosomes move to the poles
- Homologous chromosomes seperate
- Sister chromatids remain attached at the centromere
What is the centromere?
The centromere is the specialized DNA sequence of a chromosome that links a pair of sister chromatids.
What happens in telophase 1?
Two haploid cells form, each chromatid is still paired with its sister chromatid
What happens during meiosis 2?
Another round of cell division occurs resulting in 4 haploid daughter cells
How many haploid daughter cells does meiosis make?
4
What does crossing over result in?
Genetic diversity
How does crossing over occur in early prophase 1?
The duplicated chromosomes condense, Homologous chromosomes pair in a process called synapsis and are held together by proteins.
What is synapsis?
the fusion of chromosome pairs at the start of meiosis.
How does crossing over occur in middle prophase 1?
Crossing over occurs which results in new combinations of genes in each chromatid. Sister chromatids are no longer identical.
How does crossing over occur in late prophase 1?
Synapsis complex disassembles and the homologuesare held together at the site of crossing over (chiasma). The sister chromatids are held together at the centromere
What is independent assortment?
Different genes independently separate from one another when reproductive cells develop.
What does independent assortment cause?
Genetic diversity
Sexual Organisms generate diversity through what?
Crossing over, independent assortment, and random fertilisation
What are diploid organisms?
Diploid is a cell or organism that has paired chromosomes, one from each parent.
Fusions of haploid cells produced what offspring?
diploid 2n offspring
Cells in multicellular organisms need to be what?
Stably attatched to eachother
Both multicelluar and unicellular organisms need to be able to what?
Communicate and coordinate
Do plants need junctions to join cells together?
No they dont, as they dont have connectig junctions
How can cell walls communicate with one another through the cell wall?
By communication junctions
What is plasmodesmata?
a narrow thread of cytoplasm that passes through the cell walls of adjacent plant cells and allows communication between them
What are cytoplasmic bridges?
thin strand of cytoplasm linking cells as in higher plants,
What is the size exlusion limit of the plasmodesmata?
1.5kDa therefore only small signalling molecules could pass through from cell to cell
Gene expression tests have showed proteins up to 30 kDa and pieces of mRNA can move through the plasmodesmata. How?
The plasmodemata can close or open under various conditions.
Plant viruses hack what to infect neighbouring cells?
The plasmodesmata
What is Dalton Da?
A unit of molecular weight
Do animals need junctions to join cells together?
Yes in some cases.
In what cases do animals need junctions to join cells together?
For skin cells and muscle cells ect
In what cases do not animals need junctions to join cells together?
Red blood cells ect
What are tight junctions?
Connecting junctions in animal cells that form a seal to prevent the movement of liquids and material between cells. Specific proteins hold cells together forming a ‘Water Proof’ layer.
Tight junctions are important in what type of tissue?
Epithelial tissues
How do tight junctions help the blood;brain barrier?
Prevents the passage of molecules between the cells.
What are adherens junctions?
Adherens junctions are protein complexes that occur at cell–cell junctions in epithelial and endothelial tissues, usually more basal than tight junctions. Soft connection