Unit 7 Submission (N Gacek) Cell division and heredity academic report PDF

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Unit 7: Cell Division and Heredity Nikola Gacek 02/09/2020

Terms of Reference: This report discusses the topic of cell division, mitosis and meiosis, Gregor Mendel and genetics, monohybrid and dihybrid crosses (including sex linkage) and the primary source of genetic variation.

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Title Page – 1 Terms of Reference – 2 Research Methodology – 2 Findings: 2 – 11 1) 2 – 5 2) 6 – 12 Conclusion - 12 Recommendations: 12 - 13 References: 13 – 14 Bibliography: 14 - 16

Research Methodology: This assignment has been carried out using secondary research. The sources, tables, diagrams, and charts are from online articles, revision websites and educational videos. The study materials used come from learn direct and CGP A-level revision textbooks.

Findings: 1) The significance of mitosis and meiosis: Mitosis Mitosis is a process of cell duplication and reproduction where two genetically identical daughter cells are produced asexually. (Kara Rogers.cop.2020.)

It consists of six stages:

 Interphase occurs before cell division begins. DNA replicates and the centromeres form. Organelles, proteins as well as ATP are made.  In prophase, the chromosomes condense, becoming visible as coiled threads. Centrioles (tiny bundles of protein) move towards opposite ends and form a spindle, a network of protein fibres. The nuclear envelope breaks down.  During metaphase the chromosomes line up along the middle of the cell and attach to the spindle by their centromeres.  In anaphase the centromeres divide, separating into pairs of sister chromatids. The spindle contracts, pulling the chromatids to opposite ends, the centromere facing outwards.  Through telophase, chromatids reach opposite poles on the spindle, uncoiling and elongating to form chromosomes. The nuclear envelope reforms around each pair of chromosomes, the cytoplasm divides and two genetically identical daughter cells are made.  Cytokinesis shares organelles, proteins and ATP made in interphase between daughter cells, occurring at the same time as telophase. (Collins English Dictionary, 2012.)

(Figure 1; BBC bitesize, cop.2020.) Therefore, mitosis is significant for the growth and repair of cells and damaged tissue; maintenance of qualitative and quantitative ratio of genetic material between parental and offspring cells; formation of reproductive organs; keeping the chromosome number constant; cell repair of the upper epidermis, lining of the gut and red blood cells; and the physical growth of multicellular organisms.

Meiosis Meiosis is the sexual reproduction occurring in egg and sperm gametes, producing two haploid pairs, having the original number of chromosomes. During syngamy, the haploid pairs fuse, returning to the original diploid number; humans have 46 chromosomes, therefore 23 homologous pairs. One pair is a sex chromosome, XX for females and XY for males, and is not the same because it differs in shape and size (X-chromosome being the largest.)

(Figure 2; Jenny Graves, 2014.) Meiosis Stages Meiosis separates sister chromatids but unlike mitosis, it also separates homologous chromosomes in two stages: (Khan Academy, cop.2020.) 1)Meiosis I; the cell goes through interphase where it grows during the G1 phase, copies the chromosomes in the S phase, and prepares for cell division during G2 phase.  Prophase I – chromosomes condense and pair up to exchange genetic information for genetic diversity, a process called ‘crossing over.’ Chromosomes align to fit corresponding areas; the crossed over parts are held together by a protein structure called synaptonemal complex. (Khan Academy, cop.2020.)  Metaphase I, anaphase I, telophase I, cytokinesis is the same to mitosis. 2)Meiosis II process is the same to meiosis I except chromosomes do not duplicate; they separate during the phases, resulting in four haploids that are heterozygous (genetically different.)

(Figure 3; WordPress,2013.) Therefore, meiosis is significant for conserving a constant number of chromosomes in species across generations; maintaining the individuality of species; genetic recombination due to crossing over; creating genetic varieties to ensure the evolution of species; the production of gametes. 2) Heredity and Genetic variation Gregor Mendel Mendel discovered the basic principles of heredity through pea plant experiments.

(Figure 4; Wikipedia, 2020.) During the 19th century it was believed traits were passed down from parent to offspring as a mixture of characteristics and the idea of a gene did not exist. Mendel’s findings introduced the concept that inheritance of specific traits followed a certain pattern.

(Figure 5; Barrientos & Rodriguez, 2016.) Mendel chose to use pea plants because they were easy to grow, grew quickly and the seven traits were easy to observe. (Figure 5.) Pea plants reproduce sexually through pollination. Mendel controlled his experiments by transferring the pollen by hand and keeping detailed records of the process. (Kevin Beck, 2019.) Through cross pollinating yellow and green peas, Mendel found the f1 generation always had yellow peas, and the f2 generation had a 3:1 ratio of yellow to green peas because yellow is a dominant trait and green is a recessive trait. This proved Mendel’s theory that recessive traits were passed on without appearing in f1 generation first.

(Figure 6; O’neil, cop.2013.) He concluded that: 1) Inheritance was determined by ‘units’ (now genes) passed onto the offspring. 2) Offspring inherits one of each ‘unit’ from each parent. 3) The trait characteristic of the ‘unit’ might not show initially but can still be passed on. From these conclusions, Mendel discovered the three key laws of inheritance: 1) The law of segregation – inherited traits are defined by a gene pair and parental genes are randomly separated to sex cells; offspring inherit one genetic allele from each parent. 2) The law of independent assortment – genes for different traits are sorted separately and therefor the inheritance of one trait is not dependant on the inheritance of another. 3) The law of dominance – organisms with alternate alleles will always have one more dominant. Mendel’s discoveries impacted Charles Darwin’s theory of evolution by providing the mechanism for passing down traits during natural selection. (Heather Scoville, 2020.) He also had an impact on Sutton and Boveri’s (19021904) study of chromosomal theory where chromosomes exhibited a behaviour during meiosis and syngamy parallel to Mendelian’s factors of segregation and recombination. (Shruthi Arora, no date.) Mendel’s studies ultimately led to researches predicting various diseases like Archibald Garrod’s study of alkaptonuria and its inheritance. (Wikipedia, 2020.)

Monohybrid & dihybrid crosses and sex links Monohybrid crosses It is the crossing of two pure bred organisms. Punnet squares represent possible genotypes of offspring in a tabular format, each box representing one possible syngamy event; the method was developed in the 20th century. (BD Editors, 2019.) Figure 7 highlights the likelihood of a foetus being male or female. There is a 1:1 genotype and phenotype ratio; since all female gametes (homogametic)

carry the X-chromosome, the male gamete (heterogametic) determines the sex of the foetus, depending if the X or Y chromosome in the sperm fertilises the egg.

(Figure 7; Study Blue, cop.2018.) Sex linkage Sex linked alleles are found on sex chromosomes. The X-chromosome carries the most genetic information so since males only have one X copy, they have one allele for sex linked genes which is expressed even if it is recessive. Therefore, males are more likely to show a recessive phenotype. This is shown in figure 8; the female is a carrier for red-green colour blindness whereas the male has normal vision.

(Figure 8; learn direct.)

The male would express the recessive colour blindness trait, despite the male parental cell having normal vision. Dihybrid crosses These look at the probability of inheriting certain characteristics in the f2 generation when two heterozygous f1 generation are crossed. They produce a phenotypic dihybrid ratio of 9:3:3:1 and a genotypic dihybrid ratio of 1:2 : 1:2 : 4:2 : 1:2.

By crossing a yellow dominant and green recessive pea plant, f1 generation plants were all yellow though the recessive gene showed up in the f2 generation, resulting in a 9:3:3:1 ratio.

(Figure 9; learn direct.) Genetic variation Gene mutations are permanent alterations of DNA sequencing classified in two ways: 1) Hereditary mutations - Inherited from parents, present in every cell of the body.

2) Somatic mutations - Acquired and only present in specific cells. - Caused by environmental factors like exposure to UV radiation or during the replication stage of cell division. - Classified as mosaic mutations (occurring in early foetal development, potentially causing health problems) or as polymorphism mutations (genetic alterations occurring in more than 1% of the population, rarely causing any problems.) - Cannot be passed on to offspring. (BD Editors, 2017.) Gene mutations are rare and spontaneous, but their rate can be increased by mutagenic agents that change the amino acid sequence or the triplet code.

Chromosome mutations are caused by: 1) A problem occurring during meiosis. 2) Exposure to radiation, chemicals etc. These cannot be predicted and result in changing the number of chromosomes or the entire structure of a chromosome. Chromosome structure variation 1) Translocation – fragmented chromosome joins a non-homologous chromosome. 2) Deletion – chromosome breakage causes loss of genetic information. 3) Duplication – extra copies of genes form. 4) Inversion – broken chromosome segment is inserted reversed into the chromosome. 5) Isochromosome – improper division of the centromere causing two short or two long arms. Aneuploidy: occurs when the number of chromosomes is changed, caused by breakage or a non-disjunction error (homologous chromosomes do not separate properly.)

Down syndrome is a common result of a non-disjunction error and 95% of the time down syndrome is caused by trisomy-21 chromosome where there are three copies of instead of two. (Mayo Clinic, cop.2020.) Crossing over variation; occurs during meiosis in synapsis pairing, creating bivalents which wind around each other, breaking and reforming, causing a lot of variation because the genetic information is unique; with 23 chromosomal pairs there are 8.3 million possible variations.

(Figure 10; BD Editors, 2019.) Conclusion The study of genetics is key to our future as the possibilities for curing heredity diseases are endless. A common concern is the potential of creating designer babies, therefor a ‘homologous’ society; the great thing about humans is that we are all different, so if everyone started to look and act the same, we would run the risk of losing the core of who we are. Despite this, we could do a lot of good by preventing future generations from suffering with previously incurable hereditary diseases, but to do this we must understand the building blocks of who we are using genetic markers. Recommendations

I struggled including everything I wanted to say due to the word count. I need to prioritize information to stop over writing by condensing the information I want to express through reducing the amount of words I use. In the future I will use sources from the library (when they are reopened) because this would help me gain a better understanding of the content, and it would reduce my screen time, making me less tired, therefor easier to concentrate. References 

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Kara Rogers, Senior Editor, (cop.2020.) Mitosis [online.] Britannica.com. [Accessed: 26/08/2020.] Available from: https://www.britannica.com/science/mitosis 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.uk/bitesize/guides/zpkx8mn/revision/3 Collins English Dictionary, (2012.) Cytokinesis [online.] Dictionary.com. [Accessed: 26/08/2020.] Available from: https://www.dictionary.com/browse/cytokinesis Jenny Graves, (2014.) Sex, genes, the Y chromosome and the future of men [Figure 2.] TheConversation.com. [Accessed: 26/08/2020.] Available from: https://theconversation.com/sex-genes-the-y-chromosome-andthe-future-of-men-32893 Word Press, (2013.) Meiosis I and Meiosis II [Figure 3.] WordPress.com. [Accessed: 26/08/2020.] Available from: https://amoyajasmine11.files.wordpress.com/2013/06/meiosis-stages1.gif Khan Academy, (cop.2020.) Meiosis [online.] KhanAcademy.com. [Accessed: 26/08/2020.] Available from: https://www.khanacademy.org/science/biology/cellular-molecularbiology/meiosis/a/phases-of-meiosis Wikipedia, (2020.) Gregor Mendel [Figure 4.] En.Wikipedia.org. [Accessed: 26/08/2020.] Available from: https://en.wikipedia.org/wiki/Gregor_Mendel Barrentos & Rodriguez, (2016.) The Life and Works of “Gregor Mendel” [Figure 5.] ProjectInScience.Blogspot.com. [Accessed: 26/08/2020.] Available from: http://projectinscience.blogspot.com/

Kevin Beck, (2019.) The Law of Independent Assortment [online.] Sciencing.com. [Accessed: 26/08/2020.] Available from: https://sciencing.com/law-of-independent-assortment-mendeldefinition-explanation-example-13718436.html  O’Neil, (cop.2013.) Mendel’s Genetics [Figure 6.] Palomar.edu. [Accessed: 26/08/2020.] Available from: https://www2.palomar.edu/anthro/mendel/mendel_1.htm  Study Blue, (cop.2018.) Sex Chromosome [Figure 7.] StudyBlue.com. [Accessed: 26/08/2020.] Available from: https://www.studyblue.com/#flashcard/view/8076727  Learn Direct, (2019.) Sex Linkage [Figure 8.] Learn Direct. [Accessed: 26/08/2020.] Available from: Learn Direct Unit 7.  Learn Direct, (2019.) Dihybrid Crosses [Figure 8.] Learn Direct. [Accessed: 26/08/2020.] Available from: Learn Direct Unit 7.  Mayo Clinic, (2020.) Down Syndrome [online.] MayClinic.org. [Accessed: 26/08/2020.] Available from: https://www.mayoclinic.org/diseasesconditions/down-syndrome/symptoms-causes/syc-20355977  BD Editors, (2019.) Prophase II [online + figure 10.] BiologyDictionary.net. [Accessed: 26/08/2020.] Available from: https://biologydictionary.net/prophase-2/  BD Editors, (2019.) Punnet Square [online.] BiologyDictionary.net. [Accessed [31/08/2020.] Available from: https://biologydictionary.net/punnett-square/  Heather Scoville, (2020.) Biography of Gregor Mendel, Father of Genetics [online.] Thoughtco.com [Accessed: 31/08/2020.] Available from: https://www.thoughtco.com/about-gregor-mendel1224841#:~:text=Gregor%20Mendel%2C%20known%20as%20the %20Father%20of%20Genetics%2C,Austrian%20Empire%20to%20Anton %20Mendel%20and%20Rosine%20Schwirtlich.  Shruthi Arora, (no date.) Mendel Study on Genetics | Mendelian Inheritance [online.] BiologyDiscussion.com. [Accessed: 31/08/2020.] Available from: https://www.biologydiscussion.com/mendel/mendelstudy-on-genetics-mendelian-inheritance/38754  Wikipedia, (2020.) Archibald Garrod [online.] En.Wikipedia.org. [Accessed: 31/08/2020.] Available from: https://en.wikipedia.org/wiki/Archibald_Garrod 

Bibliography

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Barrentos & Rodriguez, (2016.) The Life and Works of “Gregor Mendel” [Figure 5.] ProjectInScience.Blogspot.com. [Accessed: 26/08/2020.] Available from: http://projectinscience.blogspot.com/ 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.uk/bitesize/guides/zpkx8mn/revision/3 BD Editors, (2019.) Prophase II [online + figure 10.] BiologyDictionary.net. [Accessed: 26/08/2020.] Available from: https://biologydictionary.net/prophase-2/ BD Editors, (2019.) Punnet Square [online.] BiologyDictionary.net. [Accessed [31/08/2020.] Available from: https://biologydictionary.net/punnett-square/ Collins English Dictionary, (2012.) Cytokinesis [online.] Dictionary.com. [Accessed: 26/08/2020.] Available from: https://www.dictionary.com/browse/cytokinesis Jenny Graves, (2014.) Sex, genes, the Y chromosome and the future of men [Figure 2.] TheConversation.com. [Accessed: 26/08/2020.] Available from: https://theconversation.com/sex-genes-the-ychromosome-and-the-future-of-men-32893 Heather Scoville, (2020.) Biography of Gregor Mendel, Father of Genetics [online.] Thoughtco.com [Accessed: 31/08/2020.] Available from: https://www.thoughtco.com/about-gregor-mendel1224841#:~:text=Gregor%20Mendel%2C%20known%20as%20the %20Father%20of%20Genetics%2C,Austrian%20Empire%20to %20Anton%20Mendel%20and%20Rosine%20Schwirtlich. Kara Rogers, Senior Editor, (cop.2020.) Mitosis [online.] Britannica.com. [Accessed: 26/08/2020.] Available from: https://www.britannica.com/science/mitosis Kevin Beck, (2019.) The Law of Independent Assortment [online.] Sciencing.com. [Accessed: 26/08/2020.] Available from: https://sciencing.com/law-of-independent-assortment-mendeldefinition-explanation-example-13718436.html Khan Academy, (cop.2020.) Meiosis [online.] KhanAcademy.com. [Accessed: 26/08/2020.] Available from: https://www.khanacademy.org/science/biology/cellular-molecularbiology/meiosis/a/phases-of-meiosis

 Learn Direct, (2019.) Dihybrid Crosses [Figure 8.] Learn Direct. [Accessed: 26/08/2020.] Available from: Learn Direct Unit 7.  Learn Direct, (2019.) Sex Linkage [Figure 8.] Learn Direct. [Accessed: 26/08/2020.] Available from: Learn Direct Unit 7.  Mayo Clinic, (2020.) Down Syndrome [online.] MayClinic.org. [Accessed: 26/08/2020.] Available from: https://www.mayoclinic.org/diseases-conditions/downsyndrome/symptoms-causes/syc-20355977  O’Neil, (cop.2013.) Mendel’s Genetics [Figure 6.] Palomar.edu. [Accessed: 26/08/2020.] Available from: https://www2.palomar.edu/anthro/mendel/mendel_1.htm  Shruthi Arora, (no date.) Mendel Study on Genetics | Mendelian Inheritance [online.] BiologyDiscussion.com. [Accessed: 31/08/2020.] Available from: https://www.biologydiscussion.com/mendel/mendelstudy-on-genetics-mendelian-inheritance/38754  Study Blue, (cop.2018.) Sex Chromosome [Figure 7.] StudyBlue.com. [Accessed: 26/08/2020.] Available from: https://www.studyblue.com/#flashcard/view/8076727  Wikipedia, (2020.) Archibald Garrod [online.] En.Wikipedia.org. [Accessed: 31/08/2020.] Available from: https://en.wikipedia.org/wiki/Archibald_Garrod  Wikipedia, (2020.) Gregor Mendel [Figure 4.] En.Wikipedia.org. [Accessed: 26/08/2020.] Available from: https://en.wikipedia.org/wiki/Gregor_Mendel  Word Press, (2013.) Meiosis I and Meiosis II [Figure 3.] WordPress.com. [Accessed: 26/08/2020.] Available from: https://amoyajasmine11.files.wordpress.com/2013/06/meiosisstages-1.gif...