Cellular And Genetic Mechanisms Flashcards
Disadvantages of being single celled
Limited life span
No cell replacement
Problems with increase in size
Limited specialisation
How does prokaryote bacterial division occur
Binary fission
Single DNA molecule first replicates and attaches each copy to a different part of the cell membrane
Effects of cell size on SA:v ratio
Larger the cell the Sa stays the same
So amount of energy that can enter are limited
Chromosome karyogamy
Number- constant for species
Size- of chromosomes differ, range is constant for species
Shape- of chromosome differs, pattern constant for species
3 types of centromere location
Top
Middle
Above middle
Telocentric
Metacentric
Acrocentric
What is the function of a kinetochore
Where micro tubules attach
Non localised kinetocores
Polycentromere
Holocenteomere
Poly- attach to points on chromatid
Holo- attach to any point
Centrioles/centrosome
what are they
Duplex
Made up of protein mictotubules which replicate by assembly
Plants and animals do not require,…
Centrioles for spindle formation
Microtubule organisation center in animals are
Centrosome
Electron dense cloud associated with centrioles
Essential for microtubule production
Function of spindle fibres and microtubules
Creation of spindles
Metaphase plate alignment
Orientation of chromosome for centromere splitting (independent assortment)
Chromosome movement to poles
Structure of microtubules and spindle fibres
Tubulin microtubules
Hollow tubes
2 non identical peptide chains (a and b)
Movement via tubulin
- Polymerisation
2. Depolymerisation
Movement via motor proteins
- Kinesin usually move to +ve end
2. Dyneins move to -ve end
Movement via depolymerisation
Where does it happen and what causes it
At kinetochores spindle poles
Colchicine- low levels promote depolymerisation
Astral fibres / spindle pull
What are they attached to
Astra fibres attach to cell membrane regions
Prophase 1 meiosis parts
Leptotene Zygotene Pachytene Diplotene Diakinesis
Leptotene what happens
Chromosomes condense
Each end attached to nuclear membrane by plaque
Chromo 1 and 2 find each other while it’s still attached
Attachment plaque causes the pairing
Zygotene
Initiation of synopsis formation= synaptonemal complex
Forms synapse
Genetic recob between daughter chromatids require close association
Attachment plaques moe around the membrane and bring them together
Pachytene
Synapsis complete may remain in this stage for number of days
Tetrad
4 chromosomes make up the 2 homologue chromosomes
Bilavent
Synapses homologues chromosomes before we can see 4 chromatids
Diplotene
Synaptonemal complex dissolves
Homologues still attached to chiasmata
Diakinesis
RNA synthesis stops
DNA highly condensed and detached from nuclear envelope
Importance of chiasmata
Chromosome orientation
Random assortment
Act as centromeres
Difference in mitosis and meiosis 1
Kinetochores in meiosis only on one side
Important for orientation, independent segregation and correct distribution
Difference in mitosis and meiosis 1
Second answer
Meiosis 2 independently line up, but unlike mitosis homologues not present as separated in meiosis 1
Difference in mitosis and meiosis 1
Third answer
Meiosis 1 the chiasmata divide
In meiosis 2 and mitosis the centromeres divide
Where are the oogonia held at during foetal development
Meiosis 1 initiated in all oogonia until prophase 1 diplotene
Fertilisation
Enters second meiotic division
3 polar bodies and 1 Oocyte at this point
What increases the probability of chromosome abnormality in the foetus in the number of chromosomes
Female age
Key points about female gametes
Not continuous
4 halploid 3 polar
Mitotic multiplication stage
No loss of cytoplasm (inheritance from mother)
Autopolyploid
Multiples of identical genomes
Allopolyploid
Multiple genomes of different ancestry
2 types of haploidy
Natural- bees
Artificial-
Variations in chromosome number 2 types
Aneuploidy- changes in number of a single chromosome
Euploidy- changes in entire chromosome number (genome)
Aneuploidy caused by what
Caused by non disjunction of individual chromosome
Laggards usually during meiosis 1 or 2
Forms trisomic or monosomic
Aneuploidy can occur in
Insects
Male is Xo
Euploidy Can occur in
Lizards and fish and plants
Odd genomes are not maintained caused by
Non disjunction- of whole genome/failure of cell division
Fertilisation- by more then 1 gamete
Autopolyploidy what is it
Doubling of genome
Induced in plants by colchicine
Produced diploid gametes which can self fertilise
Autotriploids AAA are often
Sterile
Allopolyploid how does it form
Species AA and species BB combine forming AABB
Mendelian rule 1
Always use 2 homozygous parents
Advantages of using pure breeds
Number of discrete traits Self fertilisation Numerous viable and fertile progeny Short generation time Can carry out cross breeding
Mendels first postulate
For each characteristic gene loci you inherit 2 alleles
Second postulate
2 alleles recessive and dominant
One show ones not in heterozygous
Complete dominance-mono hybrid inheritance
In complete dominance the recessive allele is not expressed
Mendels 3rd postulate
At gamete formation the 2 alleles segregate randomly, one to each pole
Homozygous identical
Heterozygous 50/50 chance to contain 1 allele type
