intro to genetics (3.1). gene: a heritable factor that consists of a length of dna and influences a...
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Intro to Genetics (3.1)
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• Gene: A heritable factor that consists of a length of DNA and influences a specific characteristic.
• Allele: One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene.• Example: hair color, eye color, thumb curling,
ear lobe attachment
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Comparing number of genes
• Check out the table on pg. 142.
• Which species has the greatest number genes?
• Which group has the smallest number of genes?• Why do you think this is?
• Are there any numbers that surprised you?
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Alleles
• Differences in alleles are usually changes in one or a few bases.
• Single Nucleotide Polymorphisms (SNPs) are the positions in a gene where more than one base may be present.• Several SNPs can be present in a gene.
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Comparing Genes
• Do the activity on pg. 144 “Comparing Genes”
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• Genome: The whole of the genetic information of an organism.
• The entire base sequence of each of its DNA molecules.
• In humans, the 46 molecules that form chromosomes, plus the DNA molecule in the mitochondria.
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• The entire human genome was sequenced in the Human Genome Project which began in 1990 and was completed in 2003.
• There are approx. 23,000 protein coding genes in the human genome, but most DNA is not transcribed.
• Most base sequences are the same for all humans, but SNPs are what make each person unique.
• Read about genome sequencing on pg. 148 & check out the interactive timeline (link on Haiku)
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Mutations
• New alleles are formed by gene mutations – random changes to the base sequence of a gene.
• Mutations can be:• Neutral – don’t affect the organism• Beneficial – could be good for the organism• Harmful – can even be deadly
• One type is a base substitution mutation.
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Sickle Cell ANemia
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Base Substitution Mutation
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Base substitution Mutation
• When you substitute only one base in a DNA code…
GAG
• during translation…
• amino acid: glutamic acid
• Changing one amino acid changes the shape of the whole hemoglobin protein,
• which changes the shape of the whole red blood cell.
GTG
valine
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Hemoglobin
• Oxygen that should be carried on the Hemoglobin cannot be carried as efficiently (anemia).
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• The less flexible, long shaped cells get stuck in capillaries so blood flow is inhibited.
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• Mutations can be passed to offspring.
• Here, the sickle cell gene is correlated with the frequency of malaria in Africa, where there is natural selection in favor of the gene, as it provides some protection against malaria.
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Sickle Cell Anemia
• Do the sickle cell anemia activity posted on Haiku.
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Mutations
• Causes:• Radiation: ex. Gamma rays, UV rays, X rays• Mutagenic chemicals: ex. some components of
tobacco smoke, mustard gas
• Effect: If a mutation develops in the genes that control cell division, it can cause unregulated cell division and therefore, a tumor / cancer.
• Mutations in somatic cells vs. gamete-producing cells.
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Consequences of nuclear radiation
• 1. Read about the nuclear bombings of Hiroshima and Nagasaki and the nuclear accident at Chernobyl on pg. 184 – 185.
• 2. Read the article and watch the video on the NY Times article on Chernobyl (find link on Haiku).
• 3. Read the Science Daily article on Fukushima (find link on Haiku).
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Opening Question
• Outline three results of nuclear radiation as evidenced by specific locations in the word where nuclear contamination has occurred.
• In your opinion, is the risk to the scientist’s health justified by the importance of the research?
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PRokaryotes
• Prokaryotes have one chromosome consisting of a circular DNA molecule.
• Some prokaryotes also have plasmids, but eukaryotes do not.• Plasmids are not always replicated at the same time
or at the same rate as a prokaryote’s chromosome.• Plasmids are not always passed on to both cells
formed by cell division.• Plasmids are often used in genetic engineering for
gene transfer.
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Chromosomes
• http://learn.genetics.utah.edu/content/chromosomes/
• Homo sapiens have 46 chromosomes.
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How Long is DNA?
• Read 150 – 151 in the textbook
• Summarize Carin’s technique and its importance to modern science:
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Genome size vs. number of genes
• Genome size is the total length of DNA in an organism.
• It depends on the size and number of chromosomes.
• Take a look at the table on pg. 154.
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What can we find on chromosomes?
• Finding the Loci of Human Genes: Page 154
• Go to the Haiku Link “Browse Your Genome”
• On the left side of the page, type in a gene name to search for. For ideas of genes to use, look at the purple box on pg. 154.
• Click on the gene and then scroll to the section “Genomic Content”
• Write the Location and Exon count of the gene.
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Homologous Chromosomes
• Homologous chromosomes carry the same sequence of genes, but not necessarily the same alleles.
• Diploid nuclei have pairs of homologous chromosomes.• Homo sapiens diploid cells
have 46 chromosomes.
• Haploid nuclei have one chromosome of each pair (such as in sex cells).
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Practice
• Do the DBQ on pg. 153 – Comparing the chromosomes of mice and humans.
• Do the DBQ on pg. 156 – Differences in chromosome number.
• Activity for Finding the Loci of Human Genes – see Haiku.