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Cell division
CAPE Biology Unit 1
| Question | Answer |
|---|---|
| What is mitosis? | It is the nuclear division which occurs when a cell reproduces asexually resulting in two identical cells. It is the cloning of a cell. |
| How does mitosis contribute to genetic stability? | The nuclei that are produced are identical to each other and to the parent nucleus. |
| What is binary fission/budding? | It is a form of asexual reproduction. Mitosis occurs - nucleus divides - then the cell cytoplasm divides into two separate identical cells. |
| What is protoplasm? | Nucleus + cytoplasm |
| What happens to surface area to volume ratio as cells increase in size? | It becomes smaller |
| At which stage of the cell cycle does DNA replication occur? | Synthesis (S) phase of interphase |
| What does the G phase of interphase stand for? | Growth |
| What is the purpose of replication during interphase before mitosis begins? | It produces identical DNA so the genetic information inherited by the two daughter cells is identical to that of the parent cell. |
| List FOUR roles of mitosis in multicellular organisms. | 1) Growth 2) Repair following wounding or other damage 3) Replacement of cells and tissues 4) Asexual reproduction |
| What are the 3 stages of interphase? | G1, S and G2 |
| What happens in the G1 phase of interphase? | Cell grows DNA is transcribed Protein is synthesized |
| What happens during the S phase of interphase? | DNA is replicated |
| What happens during the G2 phase of interphase? | Cell prepares for division |
| What happens during mitosis? | Cell nucleus divides |
| What happens during cytokinesis? | Cytoplasm divides |
| What is the role of proto-oncogenes in cell division? | They stimulate cell division |
| What is the role of tumour suppressor genes in cell division? | They slow down cell division |
| All cells in the body have identical genetic information EXCEPT | gametes |
| How many daughter nuclei are produced as a result of one mitotic division? | Two daughter nuclei |
| List THREE results of mitosis. | 1) Chromosome number is maintained (same in parent and daughter nuclei) 2) Genetic stability is maintained 3) No genetic variation |
| This term describes the growing tip of shoots and roots where mitosis is localized. | Meristems |
| Centrioles are NOT present in this type of cell | Plant cells |
| There is not a complete separation of cells during cytokinesis in plant cells because | they have cell walls so the membrane does not form a furrow across the cell |
| List the stages of mitosis. | 1) Prophase 2) Metaphase 3) Anaphase 4) Telophase |
| What happens in prophase? | Chromatin condenses Sister chromatids of a chromosome attach to each other at the centromere Centrioles move to opposite poles of the cell Nuclear envelope breaks up into small pieces |
| What happens in metaphase? | Chromosomes align themselves to the metaphase plate (middle of the cell) Microtubules/spindle fibres emerge from centrioles and extend from pole to pole through the centromeres of the chromosomes. |
| What happens in anaphase? | Spindle microtubules shorten, pulling sister chromatids apart. The chromatids are pulled towards opposite poles. |
| What happens in telophase? | Chromatids arrive at opposite poles and uncoil. Chromatin reappears. Nuclear envelope reforms. |
| What happens in cytokinesis? | In animal cells, the cell membrane cleaves/ furrows thereby separating the two new cells from each other. |
| What is the genetic significance of meiosis? | The number of chromosomes in the nucleus is halved. Essential for sexually reproducing organisms. This ensures that the chromosome number does not double when gametes fuse. |
| What does the suffix ploid refer to ? | The number of sets of chromosomes. |
| What is the ploidy of cells produced by mitosis? | Diploid (2n) |
| What is the ploidy of cells produced by meiosis? | Haploid (n) |
| Where does meiosis occur in humans? | In germ line cells (sex cells/gametes) |
| When does meiosis occur in humans? | The first stage starts during foetal devlopment then stops before birth. At puberty, the process continues (more on this in Reproduction topic). |
| How many pairs of chromosomes do humans have? | 23 (22 are autosomal/somatic/body cells and 1 pair are germ line/sex/gamete cells) |
| How many chromosomes do humans have? | 46 |
| What is the human haploid(n) number? | 23 |
| What is the human diploid (2n) number ? | 46 |
| In which human sex is the 23rd chromosome pair XX? | Female |
| In which human sex is the 23rd chromosome pair XY? | Male |
| What is the difference between meiosis and sexual reproduction? | Meiosis occurs BEFORE sexual reproduction ever happens. It is the halving of the chromosome number to form gametes which are haploid. In sexual reproduction, it is these gametes which fuse to restore the diploid chromosome number. |
| Why are human chromosomes diploid? | They contain two sets of chromosomes. One set is maternal in origin. The other set is paternal in origin. |
| What are the two stages of meiosis? | Meiosis I - homologous chromosomes separate Meiosis II - chromatids separate |
| How many daughter cells are produced at the end of meiosis? | Four (4) |
| List THREE results of meiosis. | 1) Chromosome number is halved 2) Daughter nuclei are genetically different from parent and each other. 3) Genetic variation arises. |
| Does the halving of chromosome number occur in meiosis I or meiosis II? | Meiosis I |
| What type of division occurs in mitosis and meiosis respectively? | Equational division and reduction division. |
| What happens in Prophase I? | Chromosomes condense and thicken Homologous chromosomes pair up Chiasmata form (crossing over occurs) between non-sister chromatids Nuclear envelope breaks down Centrioles move to opposite poles |
| What happens in Metaphase I? | Homologous chromosomes (bivalents) move to the metaphase plate (middle/equator) Random rearrangement of maternal and paternal chromosomes Microtubules attach to the centromere of each chromosome. |
| What happens in Anaphase I? | Double-stranded chromosomes from each homologous pair are pulled to opposite poles by the shortening of the microtubules. |
| What happens in Telophase I? | Chromosomes arrive at opposite poles. Nuclear envelope reforms to make two haploid daughter nuclei. |
| What happens in Prophase II? | Centrioles replicate and move to opposite poles. Nuclear envelope breaks down. |
| What happens in Metaphase II? | Chromosomes align at the equator with chromatids randomly arranged. Microtubules attach to the centromeres. |
| What happens in Anaphase II? | Sister chromatids are pulled apart and move to opposite poles by shortening of microtubules. |
| What happens in Telophase II? | Nuclear envelope reforms to give four haploid nuclei that are genetically different to each other and the parent cell. Cytokinesis may follow but not in all organisms. |
| What is a gene? | A length of DNA that codes for a polypeptide. |
| What are alleles? | Different versions/alternate forms of genes. Alleles of a gene have different DNA sequences but they occupy the same locus on homologous chromosomes. |
| What is inheritable variation? | Differences in characteristics as a result of genetic information from parents. |
| What is phenotype? | The features of an individual which are the result of gene expression and interaction between the genotype and the environment; often used to refer to the feature controlled by gene under study, may be used generally for all the features of an organism. |
| Does the environment have an effect on inheritable variation? | No. The environment only affects the phenotype not the genotype of an individual. It is genes that are passed on from parents to offspring. |
| During which specific stage of meiosis does the the pairing of homologous chromosomes occur? | Prophase I |
| During which specific stage of meiosis does separation/segregation of chromosomes occur? | Anaphase I |
| How does random segregation(assortment) of homologous chromosomes at Metaphase I of meiosis contribute to heritable variation? | Their arrangement varies. In humans, 2 to the 23rd power different combinations are possible. Each nucleus contains different mixtures of maternal and paternal chromosomes. |
| What are somatic cells? | Non-reproductive (body cells) that do not give rise to gametes, e.g. muscle cells and blood cells. |
| What are sister chromatids? | Two identical copies of a chromosome joined together at the centromere; they are identical apart from any mutation that might have occurred during replication. |
| What is a centromere? | Part of a chromosome where sister chromatids are joined |
| What is a centriole? | Organelle that organizes microtubules of the spindle for nuclear division in some eukaryotes, e.g. protists and animals, flowering plants do not have centrioles. |
| What is a chiasma? | Point of attachment between homologous chromosomes during prophase I of meiosis that results from crossing over. |
| What is a chromatid? | One of the two thread-like structures joined at the centromere that comprise a double-stranded chromosome. |
| What is chromatin? | The DNA and histone proteins that make up eukaryotic chromosomes; chromatin is packaged tightly (heterochromatin) or loosely (euchromatin) in interphase nuclei. |
| What is a chromosome? | The highest condensed, organized structure of DNA found in the nucleus of cells. |
| What is independent assortment? | The random arrangement of the alleles of two or more genes found on separate chromosomes as a result of paring of chromosomes during meiosis. |
| Define locus | The position of a gene on a chromosome. |
| What is interphase? | Stage of cell cycle when cells grow and chromosomes replicate; stage between one nuclear division and the next. |
| Define meiosis | The type of nuclear division in which homologous chromosomes pair to form bivalents in which the chromosome number is halved and variation is generated; gives rise to four nuclei that are genetically different to one another and to the parent nucleus. |
| What happens in meiosis I? | First nuclear division occurs. Homologous chromosomes separate and chromosome number is halved (from diploid to haploid) |
| What happens in meiosis II? | Second nuclear division occurs. Chromatids separate. |
| Define mitosis | The type of nuclear division that occurs in growth, asexual reproduction, tissue repair and replacement of cells; maintains the chromosome number in the daughter nuclei which are genetically identical to each other and the parent nucleus. |
| What is the segregation of alleles? | The separation of a pair of alleles during meiosis to give haploid nuclei that contain only one allele, e.g.Aa -> A and a |
| What is crossing over? | The breakage and exchange of DNA between non-sister chromatids that occurs early in prophase I of meiosis. |
| What is the genetic significance of crossing over? | It produces chromosomes with a mixture of paternal and maternal genes(greater variation in offspring). Many possible features. |
| State FOUR ways meiosis promotes variation. | 1) Alleles of a gene segregate/separate so daughter nuclei contain one of a pair of alleles. 2) Homologous chromosomes randomly segregate 3) Crossing over of non-sister chromatids of homologous chromosomes 4) Sister chromatids also separate randomly |
| List THREE features that are similar in mitosis and meiosis. | 1) During the process the nuclear envelope 'disappears' 2) DNA condenses at the start of division 3) Chromosomes are arranged at the metaphase plate |
Created by:
Ms.Kumar
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