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Back to AI Flashcard MakerBiology /LGS A-Level OCR Biology - Unit 2 - The Cell Cycle, Mitosis, Meiosis Part 4

LGS A-Level OCR Biology - Unit 2 - The Cell Cycle, Mitosis, Meiosis Part 4

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This deck covers key concepts related to the cell cycle, mitosis, and meiosis, including definitions, processes, and the importance of genetic variation.

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Define bivalent.

Homologous chromosomes that are associated in pairs physically held together with at least one crossover
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Key Terms

Term
Definition
Define bivalent.
Homologous chromosomes that are associated in pairs physically held together with at least one crossover
Define chiasmata
An x-shaped region in a homologous pair which denotes where sections of DNA have become entangled and 'crossed over', break and rejoin. Singular chias...
At what stage in meiosis are chiasmata formed?
Prophase I
Define recombiant chromatids
Chromatids with a combination of DNA from both homologous chromosomes formed by crossing over at chiasmata.
What two processes occur in meiosis to introduce genetic variation?
Crossing over Independent assortment
What is crossing over?
A genetic rearrangement between two non-sister chromatids involving the corresponding segments of DNA molecules.
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LGS A-Level OCR Biology - Unit 2 - The Cell Cycle, Mitosis, Meiosis Part 4
TermDefinition
Define bivalent.
Homologous chromosomes that are associated in pairs physically held together with at least one crossover
Define chiasmata
An x-shaped region in a homologous pair which denotes where sections of DNA have become entangled and 'crossed over', break and rejoin. Singular chiasma. Appears as a cross because sister chromatid cohesion still holds the original two sister chromatids together, even in regions beyond the crossover point.
At what stage in meiosis are chiasmata formed?
Prophase I
Define recombiant chromatids
Chromatids with a combination of DNA from both homologous chromosomes formed by crossing over at chiasmata.
What two processes occur in meiosis to introduce genetic variation?
Crossing over Independent assortment
What is crossing over?
A genetic rearrangement between two non-sister chromatids involving the corresponding segments of DNA molecules.
How does crossing over lead to genetic variation?
The genes exchanged can be different alleles so the recombiant chromosomes have different sets of alleles to the original chromatids
Besides meiosis, what are the two ways in which variation can be introduced?
Random fertilisation Gene mutation
How does random fertilisation introduce variation?
Each gamete has a unique combination of genes Any of the numerous male gametes can fertilise the egg
When does random fertilisation occur?
When the nuclei of two gametes fuse to form a zygote.
How does gene mutation introduce variation?
Bases within a gene can be altered during DNA replication.
Can mutation in the germline be inherited?
Yes e.g. inherited disease, variation - sexual cannibalism (behavioural), neck length (anatomical), production of enzyme (physiological).
Can mutation in somatic cells be inherited?
No
Why are different alleles within a population important?
They introduce genetic variation. Some combinations can provide an organism with an advantageous characteristic e.g resistance to a disease, longer neck to access food. If the environment alters organisms with favourable mutations/alleles survive. Natural selection/selection pressure/survival of fittest.
Why is meiosis important in organisms which reproduce sexually?
Results in genetically distinct haploid cells. Ensures diploid number of chromosomes is restored in fertilisation. Variation generated through crossing over and independent assortment. Allows for a genetically different zygote to be formed through the fusion of the nuclei of random gametes during random fertilisation.
Give five differences between mitosis and meiosis.
Mitosis has one cell division but meiosis has two. Mitosis maintains the original diploid chromosome number whilst meiosis halves chromosome number. Mitosis produces two daughter cells whilst meiosis produces four. Daughter cells are genetically identical to the parent cell in mitosis but genetically different in meiosis. Mitosis produces somatic cells whilst meiosis produces gametes.
Compare the genetic make up of daughter cells produced by mitosis with the original parent cell.
Genetically identical. Have same number of chromosomes. Have the same genes as the parent cell.
Why is mitosis important in the life cycle of a human?
It allows for the growth of a human. Repairs tissues. Genetically identical cells produced. Throughout life maintain chromosome number.
Why is mitosis important in the repair of tissues?
Cells produced in mitosis are genetically identical. Allows cells to carry out the same function as the parent cell. Daughter cells have the correct information to develop the same type of cell as parent cells.
What is the difference between sister and non-sister chromatids?
They have different alleles.
When does independent assortment occur?
Metaphase I and Metaphase II
Why is it important in sexual reproduction that gametes are haploid?
Without gametes less variation. Gametes fuse to form a diploid cell. Prevents doubling number of chromosome number in each successive generation.
Why does meiosis need to have twice as many stages as mitosis?
Gametes must be haploid as when they fuse a diploid cell must form. To halve the number chromosomes from 2n to n. To separate homologous pairs of chromosomes.
What is the difference between prophase I and prophase II?
In prophase I chromosomes condense to become visible and homologous chromosomes pair up to form bivalents. In prophase II the chromosomes consist of two chromatids that condense to become visible again.
Why is it important that the genetic information is checked at the checkpoints?
Otherwise mutation of a gene could occur. Which would mean a protein necessary for a particular function might not be produced. A cell could end up with too many (or little) chromosomes.
Why is replication of DNA before division of the nucleus in mitosis essential?
Cells produced are genetically identical, both daughter cells receive a full copy of the parent cell's DNA. Diploid daughter cells are produced. To maintain the chromosomal number.