TOPIC THREETOPIC THREE

Genetic ContinuityGenetic Continuity

A. Humans have 46 A. Humans have 46 chromosomes, or 23 chromosomes, or 23 homologous pairshomologous pairs..

B. Chromosome pairs B. Chromosome pairs carry alleles carry alleles for the same trait. We all have two for the same trait. We all have two alleles for each gene one from each alleles for each gene one from each parent. parent. Genes may have different

forms, for example, there are genes for blue eyes, brown eyes, green eyes and hazel eyes. The different forms of a gene are called alleles.

The diagram shows a pair of chromosomes with genes A, B and C that would each code for a different characteristic.

A1 and A2 are different alleles of the same gene. A1 might code for red hair, whilst A2 might code for brown hair.

B1 and B2 are the same genes, coding for the same characteristic, for example, freckles.

C1 and C2 are different alleles. C1 might code for straight hair and C2 for wavy hair

C. C. While genes determine our While genes determine our traits, traits, the environment can the environment can affect expression of genes.affect expression of genes.

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D. D. Each chromosome has hundreds or Each chromosome has hundreds or thousands of genes. Each gene codes thousands of genes. Each gene codes for a particular protein for a particular protein

Each shaded band has many genes located within them. The red arrows indicate the locations of the genes for breast cancer

E. E. DNA is made of 4 bases: DNA is made of 4 bases: ATCGATCG. A . A three letter three letter codon codon represents a represents a specific amino acid. Ex. specific amino acid. Ex. CAUCAU is is histidine. These amino acids are histidine. These amino acids are assembles into proteins. assembles into proteins.

F. F. Base pairs: Base pairs: AA matches up with matches up with TT, , CC matches up with matches up with GG (in RNA, A-U (in RNA, A-U and C-G)and C-G)

G. RNA G. RNA carries the genetic code to carries the genetic code to ribosomes. The ribosomes then ribosomes. The ribosomes then synthesize synthesize proteins.proteins.

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H. H. Changes to DNA are called Changes to DNA are called mutationsmutations. . They can only be passed on if they occur in They can only be passed on if they occur in reproductive cells (sperm or egg).reproductive cells (sperm or egg).

deletion insertion duplication

translocation

I. I. All cells in the body contain the same All cells in the body contain the same genes. Only some of these genes are genes. Only some of these genes are turned on, that is, your eye cells contain turned on, that is, your eye cells contain the instructions on how to make bones, the instructions on how to make bones, but only the genes to make new eye but only the genes to make new eye cells are actually turned on. We do not cells are actually turned on. We do not yet know exactly why this happens.yet know exactly why this happens.Click on image for a video

J. Selective breeding J. Selective breeding produces produces animals and plants with desired traits animals and plants with desired traits (disease resistance, larger fruit, more (disease resistance, larger fruit, more meat or milk, specific colors).meat or milk, specific colors).

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K. Genetic engineering K. Genetic engineering or or gene gene splicing splicing inserts genes of one organism inserts genes of one organism into the genes of another. Enzymes are into the genes of another. Enzymes are used to cut and copy the DNA segments. used to cut and copy the DNA segments. Bacteria are often used because they Bacteria are often used because they have no nucleus protecting their DNA and have no nucleus protecting their DNA and they reproduce very quickly, allowing they reproduce very quickly, allowing large amounts of medicine (insulin) to be large amounts of medicine (insulin) to be made.made.

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a. The example of gene splicing: a. The example of gene splicing: The The gene to make human insulin was gene to make human insulin was inserted into bacteria. These inserted into bacteria. These bacteria canbacteria can now make insulin that is now make insulin that is exactly the same as human insulin. exactly the same as human insulin. This insulin is used byThis insulin is used by diabetics. This diabetics. This is safer than the cow and sheep is safer than the cow and sheep insulin that were used in the past.insulin that were used in the past.

L. L. New technologies ex. (New technologies ex. (electrophoresis electrophoresis a tool that allows scientists to separate a tool that allows scientists to separate DNA according to size) are making it DNA according to size) are making it easier to diagnose and treat genetic easier to diagnose and treat genetic disease, though we cannot yet cure them.disease, though we cannot yet cure them.

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