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TOPIC 3 Genetics 15 hours

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1 TOPIC 3 Genetics 15 hours

2 3.1 Genes 3.2 Chromosomes January 29th/2015 Adapted from: Taylor, S. (2009). Chromosomes, Genes, alleles and mutations (Presentation). Science Video Resources. [Online] Wordpress.

3 Genetic information Eukaryote chromosomes are made of DNA and proteins. The chromosome is composed of two main molecules. a) DNA b) Proteins called histones. This image was taken shortly after DNA a replication but before the prophase. It is composed of two daughter chromatids joined at the centromere. The chromosome is super coiled by a factor around x16,000. The DNA molecule is about 1.8m long but is located in the nucleus which is only 10um in diameter! m#one

4 ALLELE are the various specific forms of a gene A heritable factor that consists of a length of DNA and influences a specific characteristic A gene occupies a specific position on a chromosome Alleles differ from each other by one or only a few bases New alleles are formed by mutation. i


6 4.1.3 Define gene mutation.


8 4.1.4 Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia.





13 Homologous chromosomes have the same genes as each other, in the same sequence, but not necessarily the same alleles of those genes. 4.2.2 Define homologous chromosomes. 10%20Exam%20Reviews/Exam%201%20Review/Ch03%20Mitosis%20and%20T he%20Cell%20Cycle.htm

14 The two DNA molecules formed by DNA replication prior to cell division are considered to be sister chromatids until the splitting of the centromere at the start of anaphase. After this, they are individual chromosomes.

15 Karyogram Pictures can be taken of the human chromosomes during the metaphase. They can then be arranged into pairs on the basis of size and structure. The chromosomes appear as pairs of sister chromatids. There are 23 pairs (46 chromosomes) therefore this is human. In this case the 23 rd pair in this case are one long pair of chromatids (X- chromosome) and one very short (Y chromosome). Females = XX Males = XY SHORT ANIMATION: th/~bio/assets/karyot ype_mutation.swf SHORT ANIMATION: th/~bio/assets/karyot ype_mutation.swf






21 HOMEWORK: in your notebook, for Wednesday 11th of February. 1. Print an image of what you find and analyze the results.

22 2. Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica. Remember that genome size refers to the total amount of DNA of a species or organism. This comparison must be in your notebook.

23 3. Print an image of what you find and analyze the results. http://www.ebi. /clustalo/

24 4. Prepare this question: Explain the causes of sickle-cell anemia. (8)

25 Markscheme: caused by gene mutation; (sickle-cell anemia) due to a base substitution (mutation); changes the code on the DNA; which leads to a change in transcription / change in mRNA; which (in turn) leads to a change in translation / change in polypeptide chain/protein; (the tRNA) adds the wrong amino acid to the polypeptide chain; glutamic acid replaced by valine; produces abnormal hemoglobin; causing abnormal red blood cell/erythrocyte shape / sickle shape; which lowers the ability to transport oxygen; sickle-cell allele is codominant; homozygote/HbS HbS have sickle cell anemia/is lethal / heterozygote/ HbS HbA has the sickle trait/is carrier (and is more resistant to malaria); 8 max Write it down in your notebook

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