Unit 7 - Cell Division and Heredity PDF

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Unit 7 - Cell Division and Hereditary assignment,...

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Cell Division and Heredity By Orla Mulroe 14/01/2022

Table of contents

Introduction...................................................................................2 Cell Division………………………………………………………………………………….3 Mitosis...........................................................................................4 Meiosis..........................................................................................5 Heredity and genetic variation........................................................................................6 Monohybrid and dihybrid crosses including sex linkages…………….......................................................7 Variation and mutations.....................................................................................10 Conclusion....................................................................................11 References....................................................................................11

Introduction The aim of this report is to demonstrate understanding of cell division by giving a description of both mitosis and meiosis and their significance. As well as demonstrate understanding of heredity and genetic variation through description of the following areas: •

The impact of one geneticist on our understanding of genetics.

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Monohybrid and dihybrid crosses including sex links.

• The main sources of variation, including cross over, and gene and chromosome mutations.

Cell Division Cell division is the process by which the parent cell reproduces two daughter cells, and both share the same DNA just as the parent. There are three main function that composes cell division: •

Reproduction

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The repair of tissues and its growth

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The formation of gametes

Cell division is generally associated with Mitosis although not exclusively as it also occurs in meiosis.

Appendix 1.Mitosis vs. Meiosis (Latham, 2021)

Mitosis Mitosis is the process of cell division in which the parent cell divides into two genetically identical daughter cells.

Appendix 2.Mitosis (Latham, 2021) Mitosis starts with Interphase, which is not really classed as a phase of Mitosis, and occurs over 3 stages

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Appendix 3, Stages of Interphase (BB Editors, 2017)

Gap 1 (G1 – Where majority of the protein synthesis happens and the size of the cell duplicates Synthesis (S) – Normal functioning of the cell is paused, and replication of the DNA begins. The cells chromosomes are duplicated in preparation of the cells division. Gap 2 (G2) – This is the stage between the completion of DNA synthesis and the decision to divide

After the interphase stage, there are 5 phases of mitosis -

prophase,

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prometaphase

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metaphase,

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anaphase,

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telophase.

Prophase – The cell begins to break down and build up structures getting itself prepared for the division of the chromosomes. The chromosomes then start to condense, and the mitotic spindle starts to form. The spindle is a structure that is made of strong fibres that are part of the cell’s skeleton and its job is to organise the chromosomes and move them around during mitosis. The nucleolus then disappears which shows that the nucleus us getting ready to break down. Prometaphase – The mitotic spindle starts to organise the chromosomes and the chromosomes start to become more condense. The nuclear envelope breaks down releasing the chromosomes and the microtubules start to capture the chromosomes. Metaphase – The spindle has captured all the chromosomes and lined them in the middle of the cell in preparation for them to be divided. Before proceeding to the next phase, the cell checks to ensure that all chromosomes are at the metaphase plate (term used for the area of the cell where the chromosomes line up) and their kinetochores are correctly attached to the microtubules. This is to ensure that the sister chromatids split evenly between the 2 daughter cells when they sperate at the next phase Anaphase – The sister chromatids separate from each other and are pulled to opposite ends of the cell, and each is now its own chromosome. Telophase – The cell starts to re-establish its normal structure and at this point Cytokinesis takes place. (Cytokinesis is the division of cytoplasm to form two new cells, overlapping with the final stages of mitosis which may start in either anaphase or telophase.) The mitotic spindle breaks down and 2 new nuclei form, one for each set of chromosomes, and the nuclear membrane and nucleoli reappear.

Meiosis Meiosis is the process of the reproductive cells. Gametes such as ova, sperm, and pollen begin as germ cells, which, like other types of cells, have two copies of each gene in their nuclei, during this process, the number of chromosomes is halved throughout the separation of similar chromosomes in a diploid cell. Meiosis is divided by two: Meiosis1 and Meiosis2. After these processes, the diploid cell splits into four haploid cells; these processes are similar to mitosis, however the stages are doubled. (Cooper, 2019)

Heredity and genetic variation Our understanding of genetics is derived from a study carried out by Gregor Mendel. In 1866, Mendel published the results of years of experimentation in breeding pea plants. Mendel chose pea plants as they grew quickly, were hermaphroditic, monohybrid crosses and their seven characteristics were easily identified, shown in appendix 4.

Appendix 4, Mendel’s Garden Pea Plant Experiment (Biologydictionary.net, No Date) Mendel started by cross breeding green and yellow plants and discovered that 100% of the offspring plants (F1 Generation) were yellow. The following set of offspring plants (f2 Generation) had a 3:1 ration of Yellow to Green peas. Mendel used the lows of probability to show that when the sex cells are formed, the factors for each trait that an individual inherits from its parents are separated into different sex cells. When the sex cell united at conception the resulting offspring will have two factors for each trait. Mendel’s principle of dominance explained that most traits are not a blend of the father’s traits and those of the mother as was commonly thought. Instead, when an offspring inherits a factor for opposing forms of the same trait, the dominant form of that trait will be apparent in that individual. The factor for the recessive trait, while not apparent, is still part of the individual’s genetic makeup and may be passed to offspring. (Bagley,2013)

Monohybrid and dihybrid crosses including sex links. A monohybrid cross is where two individuals who have homozygous genotypes or genotypes that have completely dominant or completely recessive alleles, which result in opposite phenotypes for a certain genetic trait. Traits are characteristics determined by discrete segments of DNA called genes. Allele is an alternate version of a gene inherited during sexual reproduction. Male and female gametes, produced by meiosis, have a single allele for each trait. Punnet squares, such as the one shown in Appendix 5 is a table used to predict the genotypes and phenotypes of the offspring in a genetic cross involving specified traits.

Appendix 5, Monohybrid Cross (Anon, 2020) Dihybrid Cross differs from the monohybrid cross as the dihybrid cross looks for the probability of inheriting 2 characteristics or traits in the F2 generation when two heterozygous f1 generations are crossed, whereas the monohybrid only shows a single genetic character or trait. As shown in appendix 6, when crossing the Round Yellow dominant pea plant with the recessive wrinkled green pea plant, the dominant round yellow gene comes through in the F1 generation, only when we get to the F2 generation that the recessive green pea plant appears again giving a phenotype ratio of 9:3:3:1

Appendix 6, Dihybrid cross in pea plant (Sapkota, 2021) Sex Linkage Sex linkage is the phenotypic expression of an allele that is dependent on the gender of the individual and is located on the sex chromosome. (Wikipedia, the free encyclopaedia, no date) Humans have 23 pairs of chromosomes, 22 pairs of autosomal chromosomes and a pair of sex chromosomes. In females the sex chromosome is XX and in males it is XY.

Sex linked traits are on the X chromosomes because it is larger and has more genes. The mother passes down an X chromosome and the father would pass down either an X or a Y chromosome which would determine the child’s gender. As majority of the genes are carried on the X chromosome therefore genetic abnormalities and diseases are passed down through the X chromosome. Many non-sex determining Xlinked genes are responsible for abnormal conditions such as haemophilia. As shown in appendix 7, if a male inherits this disease, then it has been passed down from his mother, since it is passed down through the X chromosome, as stated previously.

Appendix 7, (PMT Education, No Date)

Variation and Mutation Genetic variation is the basic mechanisms of evolutionary change to function – Genetic variation can be identified through either continuous or discrete traits. (Loewe, 2008) There are 3 main sources of genetic variation - Mutations - changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations. Mutations are changes in the genetic sequence, and they are a main cause of diversity among organisms. - Gene flow - movement of genes from one population to another and is an important source of genetic variation. - Sex - introduces new gene combinations into a population. A chromosome mutation is a change that occurs in a chromosome that cannot be predicted and are caused by problems that occur during meiosis, or by agents which can cause mutations, such as chemicals, radiation etc. Chromosome mutations can result in changes in the number of chromosomes in a specific cell, or in the structure of a chromosome. Whilst gene mutations alter a single gene or larger segment of DNA on a chromosome, chromosome mutations affect the entire chromosome (Bailey, 2019) Mutation that affects all genes in chromosomes: -

Inversion – Broken segment of a chromosome is reversed and reinserted Deletion - Part of the chromosome is lost resulting in the absence of all the genes in that area Duplication – Extra copies of the chromosome is repeated, resulting in an increase of genes in that region Translocation – Part of the Chromosome is attached to another chromosome.

Conclusion The study of genetics can have a significant impact on the future of humanity and all living things. Having the ability to understand the complex process of cell division and hereditary can be vital in playing a part in not only curing diseases but preventing them in the first place. As mutation can vary within a genome and between genomes, more in depth work and study is required before researchers can obtain more precise estimates of the frequencies of different mutations and it is vital that this work and study continues so the future generations can be provided with the knowledge and tools to combat hereditary disease. A downside to the study of genetics is the potential of creating offspring with specific traits requested by the parents which could lead to the risk of human individuality being a thing of the past. In the future, doctors and scientists need to use our genetic information to diagnose, treat, prevent, and cure many illnesses. Genes are instructions, which tell the body how to make all the proteins it needs to survive and grow.

Recommendation The study material provided for the course gave an easy-to-understand insight into the subject, I found however, conducting my own research provided me with a more in depth understanding. Taking a more visual approach with the use of educational videos, charts and diagrams helped me grasp the information that the text was explaining. I also found that looking at different research and articles helped me understand due to the various ways the knowledge and research was presented. I did however find myself going back and forth between websites, where in future I will stick to looking at one thing at once as I was getting my wires crosses on occasion with the multiple tabs that I had opened.

References Bagley, M. (2013), “LiveScience”. Available from https://www.livescience.com/27332genetics.html Accessed on 05/01/2022

BBC Bitesize, (cop.2020.) Cell Division: the stages of mitosis in detail [Figure 1.] BBC.co.uk. [Accessed: 26/08/2020.] Available from:

https://www.bbc.co.u k/bitesize/guides/zpk x8mn/revision/3 BBC Bitesize, (2020) “Cell Division: the stages of mitosis in detail” Available from https://www.bbc.co.uk/bitesize/guides/zpkx8mn/revision/3 Accessed on 04/01/2022 Cooper, J. A. (2019), “Encyclopedialike Britannica”. Available from https://www.britannica.com/science/cell-biology/Cell-division-and-growth Accessed on 04/01/2022 Regina Bailey, 2012, “How Chromosome Mutations Occur”, Available from https://www.thoughtco.com/chromosome-mutation-373448, Accessed on 05/01/2022 Wikipedia, the free encyclopaedia. (No date), “ScienceDaily”. Available from https://www.sciencedaily.com/terms/sex_linkage.htm Accessed on 05/01/2022

Bibliography Anon, (2020). “The Punnett Square Approach for a Monohybrid Cross”. Available from https://bio.libretexts.org/@go/page/13264 Accessed on 05/01/2022 Bagley, M. (2013), “LiveScience”. Available from https://www.livescience.com/27332genetics.html Accessed on 05/01/2022

BBC Bitesize, (cop.2020.) Cell Division: the stages of mitosis in detail

[Figure 1.] BBC.co.uk. [Accessed: 26/08/2020.] Available from: https://www.bbc.co.u k/bitesize/guides/zpk x8mn/revision/3 BBC Bitesize, (2020) “Cell Division: the stages of mitosis in detail” Available from https://www.bbc.co.uk/bitesize/guides/zpkx8mn/revision/3 Accessed on 04/01/2022 BB Editors (2017) “Interphase” Available from https://biologydictionary.net/interphase/ Accessed on 04/01/2022 Biologydictionary.net (No Date), “DNA and Chromosomes in Inheritance” Available from https://biologydictionary.net/ngss-high-school-tutorials/ls3-1-dna-and-chromosomes-ininheritance/# Accessed on 05/01/2022 Cooper, J. A. (2019), “Encyclopedialike Britannica”. Available from https://www.britannica.com/science/cell-biology/Cell-division-and-growth Accessed on 04/01/2022 Latham,K, (2021), “Mitosis vs. Meiosis”, Available from https://biologydictionary.net/mitosisvs-meiosis/ ccessed on 04/01/2022 Loewe, L. (2008), “Genetic Mutation”. Available from Nature Education: https://www.nature.com/scitable/topicpage/genetic-mutation-1127 Accessed on 05/01/2022

PMT Education, (No Date), “Genetics, Populations, evolution and ecosystems”. Available from https://pmt.physicsandmathstutor.com/download/Biology/A-level/Notes/AQA/7Genetics-Populations-Evolution-and-Ecosystems/Summary%20Notes.pdf Accessed on 05/01/2022 Regina Bailey, 2012, “How Chromosome Mutations Occur”, Available from https://www.thoughtco.com/chromosome-mutation-373448, Accessed on 05/01/2022 Sapkota, A (2021), “Dihybrid Cross- Definition, Steps and Process with Examples”, Available from https://microbenotes.com/dihybrid-cross/ Accessed on 05/01/2022 Wikipedia, the free encyclopaedia. (No date), “ScienceDaily”. Available from https://www.sciencedaily.com/terms/sex_linkage.htm Accessed on 05/01/2022

Appendices Anon, (2020). “The Punnett Square Approach for a Monohybrid Cross”. Available from https://bio.libretexts.org/@go/page/13264 Accessed on 05/01/2022 BB Editors (2017) “Interphase” Available from https://biologydictionary.net/interphase/ Accessed on 04/01/2022 Biologydictionary.net (No Date), “DNA and Chromosomes in Inheritance” Available from https://biologydictionary.net/ngss-high-school-tutorials/ls3-1-dna-and-chromosomes-ininheritance/# Accessed on 05/01/2022 Latham,K, (2021), “Mitosis vs. Meiosis”, Available from https://biologydictionary.net/mitosisvs-meiosis/ ccessed on 04/01/2022 Loewe, L. (2008), “Genetic Mutation”. Available from Nature Education: https://www.nature.com/scitable/topicpage/genetic-mutation-1127 Accessed on 05/01/2022 PMT Education, (No Date), “Genetics, Populations, evolution and ecosystems”. Available from https://pmt.physicsandmathstutor.com/download/Biology/A-level/Notes/AQA/7Genetics-Populations-Evolution-and-Ecosystems/Summary%20Notes.pdf Accessed on 05/01/2022 Sapkota, A (2021), “Dihybrid Cross- Definition, Steps and Process with Examples”, Available from https://microbenotes.com/dihybrid-cross/ Accessed on 05/01/2022...