LGS A-Level OCR Biology - Unit 2 - The Cell Cycle, Mitosis, Meiosis Part 3
This deck covers key concepts from Unit 2 of the A-Level OCR Biology syllabus, focusing on the cell cycle, mitosis, and meiosis. It includes definitions, processes, and functions related to cellular reproduction and genetic variation.
What are 4 functions of mitosis?
Key Terms
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| Term | Definition |
|---|---|
What are 4 functions of mitosis? | Growth of an organism
Repair/replacement of tissues
Asexual reproduction
Development of embryos |
How do yeast undergo mitosis? | Yeast reproduces asexually through mitosis
A bud forms before DNA replicates
One large and one small cell are produced |
What is mitosis in bacteria called? | Binary fission |
Define diploid | Normal chromosome number, two chromosomes of each type inherited from each parent |
Define haploid | Half the normal number of chromosomes, one chromosome of each type |
Define gametes | Haploid sex cell produced by meiosis in organisms that reproduce sexually |
Define meiosis | Form of cell division where the nucleus divides twice resulting in a halving of chromosome number and producing 4 haploid cells |
Define reduction division | The first cell division in meiosis, the process by which germ cells are formed.
Cell division resulting in the production of haploid cells from a diploid cell |
Define zygote. | The initial diploid cell formed when the nuclei of gametes fuse during the fertilisation stage of sexual reproduction. |
How many rounds of cell division occur in meiosis? | 2 |
What occurs in prophase I of meiosis? | Chromosomes begin to condense, and homologs loosely pair along their lengths, aligned gene by gene Synapsis - Pair homologs become physically connected to each other along their lengths by a 'zipper-like' protein structure Crossing over, genetic rearrangement between non-sister chromatids, leaving at chiasmata 'x-shaped' regions at the point of crossover Centrosome movement, spindle formation and nuclear membrane disintegration Bivalents are formed |
What occurs in metaphase I of meiosis? | Pairs of homologous pairs of chromosomes line up along the metaphase plate, with one chromosome in each pair facing each pole Both chromatids of one homolog are attached to kinetochore microtubules from one pole; those of the other homolog are attached to microtubules from the opposite pole |
What occurs in anaphase I of meiosis? | Breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows homologs to separate Spindle fibres pull homologous chromosomes to opposite poles Random assortment of alleles as pairs move apart Sister chromatid cohesion persists at the centromere, causing chromatids to move as a unit toward the same pole |
What occurs in telophase I of meiosis? | Starts with each half of the cell having a complete haploid set of duplicated chromosomes Each is composed of two sister chromatids; one or both chromatids include regions of non-sister chromatid DNA Cytokinesis occurs simultaneously forming two haploid daughter cells (which are unidentical) Nuclear envelope reforms |
What occurs in prophase II of meiosis? | Chromosomes, which still consist of two chromatids, recondense Nuclear membrane disintegrates A spindle apparatus forms from centrosomes Chromatids start to move towards the metaphase plate II |
What occurs in metaphase II of meiosis? | Pairs of chromatids line up along the (equatorial) metaphase plate as in mitosis Because of crossing over in meiosis I, the two sister chromatids are not genetically identical Random assortment of homologous chromosomes at the metaphase plate is the second mechanism that introduces variation into the gametes = Independent assortment |
What occurs in anaphase II of meiosis? | Breakdown of proteins that hold the sister chromatids together at the centromere Allows chromatids to be pulled apart by spindle fibres The chromatids move towards opposite poles as individual chromosomes |
What occurs in telophase II of meiosis? | Nuclei form, the chromosomes begin decondensing, and cytokinesis continues Mitotic division of one parent cell to produce four haploid daughter cells which are genetically distinct from each other |
How does independent assortment occur? | The random arrangement of bivalents/homologs at the metaphase plate. |
How does independent assortment lead to variation? | Different alleles can face the poles e.g. the maternal or paternal chromosomes can therefore end up at either pole during anaphase. |