Lesson 4A Chromosome, DNA & Gene

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1 Lesson 4A Chromosome, DNA & Gene

2 Chromosome, Gene and DNA Chromosome: A thread-like structure made mostly of DNA Found in the nucleus

3 Chromosome, Gene and DNA DNA: Deoxyribonucleic acid Materials found in chromosomes that contain genetic code

4 Chromosome, Gene and DNA Gene: A segment of DNA that controls protein production Determines a characteristic (e.g. eye colour)

5 Chromosome DNA Genes

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7 Chromosome Structure centromere gene chromosom e chromatids

8 Chromosome Number Each organism has a specific number of chromosomes. Chromosomes come in pairs homologous pairs Human cells have 23 pairs (46 chromosomes) Dogs have 39 pairs (78 chromosomes) Homologous pair

9 Chromosome Number Sex Cells: gametes (egg or sperm cells) contain 23 chromosomes that are not paired HAPLOID CELLS Somatic Cells: body cells (muscle, skin, blood...etc.) contain 46 chromosomes in humans DIPLOID CELLS

10 Human Chromosomes: 23 pairs of chromosomes Male and Female

11 DNA Structure 1953 James Watson and Francis Crick created a model of DNA: Twisted ladder shape called double helix Basic building block of DNA nucleotide Each nucleotide is made of o nitrogenous bases adenine (A) thymine (T) cytosine (C) guanine (G) o deoxyribose sugar o phosphate

12 Sugar-phosphate backbone Nitrogenous base hydrogen bonds

13 DNA Structure

14 DNA Structure Sides of the ladder : Sugar + phosphate molecule Rung of the ladder : Nitrogenous bases form pairs that hydrogen bond to one another A always pairs with T (by 2 hydrogen bonds) C always pairs with G (by 3 hydrogen bonds)

15 Side: sugar + phosphate rung : nitrogenous bases Sugar-phosphate backbone Base pairs Sugar-phosphate backbone

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17 Why is DNA Important? Each DNA molecule contains hundreds or thousands of genes. Genes decide what kinds of proteins your cells can make, and therefore how your body might function or look. Examples: Genes controls your features (hair and eye colour), and whether you can digest certain foods (milk). The order of A, T, C, G building blocks in a gene is the genetic code (message) that determines the specific proteins the cells can make

18 A hydrogen bond C T A sugar phosphate G base pair C

19 DNA Structure

20 DNA : The Double Helix Note: The Structure of DNA allows DNA to easily and accurately replicate during cell division

21 DNA Mutations & DNA Screening

22 DNA Mutations DNA Mutations: A change in the usual order of the A, C, T, G building blocks. A mutation in a gene can alter the protein structure it produces, and can then affect how well the protein does its job. Example: Sickle cell anemia

23 DNA Mutations

24 What Causes DNA Mutations? Mutations are caused by mutagens, substances that physically damage DNA, such as electromagnetic radiation (X-rays, UV rays), chemicals (mercury, tar in cigarettes) Mutations can affect only one or a few cells OR affect eggs and sperm that are passed between generations (inherited)

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27 DNA Mutations Gene mutations are at least partly blamed for a variety of diseases.

28 DNA Screening DNA screening: To test someone whether they have genes associated with certain genetic disorders. Examples of genetic disorders: Down syndrome, Huntington disease

29 Examples of genetic disorders: Down syndrome: have 47 chromosomes (extra chromosome leads to overproduction of certain proteins) results in physical and developmental disabilities

30 Examples of genetic disorders: Phenylketonuria (PKU): No enzyme to digest certain kinds of proteins in foods build-up of phenylalanine can lead to brain damage

31 Examples of genetic disorders: Huntington disease: Abnormal gene produces a protein (huntingtin) in the brain; affects nerve cells loss of muscular control and brain function

32 Examples of genetic disorders: Cystic fibrosis: Abnormal gene produces too much mucus that clogs the lungs, prevents food from being digested, and damages the reproductive system

33 Issues in DNA Testing for Huntington Disease: To Test or Not to Test? Arguments For DNA Testing Arguments Against DNA Testing

34 Issues in DNA Testing for Huntington Disease: To Test or Not to Test? Arguments For DNA Testing Arguments Against DNA Testing Can reduce uncertainty Can cause emotional pain since there is no cure May change many of a person s life decisions Testing is too expensive since it cannot save lives Test results may be used to discriminate against a person Test results may not be 100% certain (cancer)

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