Mitosis and Fertilisation Flashcards
What happens in Interphase?
- DNA is unravelled and replicated (as well as organelles), to double its genetic content
- ATP is increased
What happens in Prophase?
- The chromosomes condense, getting shorter and fatter
- Tiny bundles of proteins called centrioles start moving to opposite ends of the cell, this forms a network of protein fibres called spindles
- The nuclear envelope breaks down
What happens in Metaphase?
- The chromosomes line up along the middle of the cell and becomes attached to the spindle by their centromere
What happens in Anaphase?
- The centromeres divide, separating each pair of sister chromatids
- The spindles contract, pulling chromatids to opposite ends of the spindle
What happens in Telophase?
- Chromatids uncoil and become long and thin, they are now called chromosomes again
- A nuclear envelope forms
What happens in Cytokinesis?
- The cytoplasm divides and there are now 2 daughter cells that are genetically identical
What does the cell cycle consist of?
- Cell growth
- DNA replication
- Cell division
What are the 2 checkpoints of the cell cycle called and what do they do?
- M and S
- Prevents uncontrolled cell division
- Detect and repair damage to DNA by prevent reversal of cell cycle and making sure DNA is only duplicated once
Other than being a checkpoint what else does M phase do?
- Cell growth stops
- Nuclear division occurs
Other than being a checkpoint what does S phase do?
- DNA replicates
- Once the cell enters this stage it is committed to the cell cycle
What happens in G2 phase of the cell cycle?
- Cell keeps growing
- Proteins needed for cell division are made
What happens in G1 phase of the cell cycle?
- Cell grows and duplicates
- P53 tumour supressed gene triggers and controls checkpoints
- Transcription
What are telomeres and where are they found?
- Telomeres are ‘protective tips’ found on the ends of chromosomes
- Each time DNA replicates the telomere becomes shorter and eventually will become so short that they cannot carry out their function anymore
What happens to telomeres in cancer cells?
In cancer cell the enzyme telomerase which ordinarily prompts the shortening, the enzyme will maintain telomere length and the cell has infinite replicative potential
What is Hayflick’s constant?
The number of times that DNA can replicate before telomeres break down (around 50 times)
Describe the process of fertilisation?
- Acrosome reaction = enzymes in acrosome digest the zona pellucida, sperm nucleus enters egg cell
- Cortical reaction = cortical granules are released by the egg membrane that causes the zona pellucida to harden, preventing polyspermy
- Nucleic fusion = restoring full set of chromosomes, diploid zygote
How are mammalian eggs adapted to its function?
- Zona pellucida (protective coating) to prevent polyspermy
- Haploid nucleus to restore full set of chromomes
- Has nutrients in cytoplasm for embryo
How are sperm adapted to its functions?
- Hydrodynamic shape for reduced resistance
- Haploid chromosomes
- Mitochondria to provide energy
- Acrosome to provide digest zona pellucida
- Flagellum for motility
- Membrane has receptors
What is a locus?
The position on a chromosome occupied by a gene
What is meant by autosomal linkage?
Two or more genes are located on the same (non-sex) chromosome
What is meant by sex-linkage?
Where an allele is located on one of the sex chromosomes
What is meant by polygenic inheritance?
The kind of inheritance in which the trait is produced from the cumulative effects of many genes
Describe 2 types of phenotypic variation?
Continuous = variation exists as gradual changes
Discontinuous = variation exists as distinct categories
In which ways does meiosis ensure genetic variation?
- Crossing-over alleles between chromatids
- Independent assortment of chromosomes
At the start of fertilisation, many sperm cells will surround the ovum.
i) Describe the events of fertilisation that occur after the acrosome reaction.
- Sperm cell fuses with membrane
- Exocytosis of cortical granules
- Zona pellucida hardens to avoid polyspermy
Animals produce haploid gametes by meiosis.
i) Explain how meiosis gives rise to genetic variation in gametes.
- Independent assortment gives rise to new combinations of chromosomes
- Crossing over involves swapping sections of chromosomes
Explain what is meant by the term polygenic inheritance.
- More than one gene for a single characteristic
- Different loci
What is the process of protein trafficking?
- The ribosomes on the rER make proteins that are excreted
- New proteins are folded and processed in the rER
- They’re transported from the rER to the Golgi in vesicles
- At the Golgi they are modified
- They are transported to the cell surface where they are excreted
