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Definitions <ul><li>Genotype: The alleles of an organism. </li></ul><ul><li>Phenotype: The characteristics of an organism. </li></ul><ul><li>Dominant allele: an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state. E.g. Bb and BB give brown hair. </li></ul>
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<ul><li>Recessive allele: An allele that only has an effect on the phenotype when present in the homozygous state. E.g. bb gives you blond hair. </li></ul><ul><li>Codominant alleles: Pairs of alleles that both affect the phenotype when present in a heterozygote. E.g. C R C W gives a pink flower because both red and white genes are codominant. </li></ul><ul><li>Locus: The particular position on homologous chromosomes of a gene. </li></ul>
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<ul><li>Homozygous: Having two identical alleles of a gene. </li></ul><ul><li>Heterozygous: Having two different alleles of a gene. </li></ul><ul><li>Carrier: An individual that has only one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for the allele. </li></ul><ul><li>Test cross: Testing a suspected heterozygote by crossing it with a known homozygous recessive. </li></ul>
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A monohybrid cross <ul><li>Cross a smooth and wrinkled seed together. Then cross the offspring with each other: </li></ul>
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Performing crosses <ul><li>1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring? </li></ul>
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Performing crosses <ul><li>1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring? </li></ul><ul><li>P 1 Tt x tt </li></ul>T t t
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Performing crosses <ul><li>1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring? </li></ul><ul><li>P 1 Tt x tt </li></ul>T t t t t t T
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Performing crosses <ul><li>1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring? </li></ul><ul><li>P 1 Tt x tt </li></ul>T t t t t t T Tt Tt Tt tt
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Performing crosses <ul><li>1. A heterozygous tall pea plant is crossed with a homozygous short pea plant. What are the F 1 offspring? </li></ul><ul><li>P 1 Tt x tt </li></ul>T t t t t t T F 1 Results: ½ Tt – Tall pea plants ½ tt – short pea plants Tt Tt Tt tt
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Multiple Alleles <ul><li>Some genes have more than two alleles. </li></ul><ul><li>E.g. Human blood types. </li></ul><ul><li>Type A = I A I A or I A i </li></ul><ul><li>Type B = I B or I B i </li></ul><ul><li>Type AB = I A I B </li></ul><ul><li>Type O = ii </li></ul>
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ABO blood groups <ul><li>An example of multiple alleles and codominance. </li></ul><ul><li>The blood type AB is codominant because both A and B are expressed phenotypically. </li></ul>
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Performing crosses <ul><li>2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A? </li></ul>
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Performing crosses <ul><li>2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A? </li></ul><ul><li>P 1 I A I B x ii </li></ul>I A I B i
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Performing crosses <ul><li>2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A? </li></ul><ul><li>P 1 I A I B x ii </li></ul>I A I B i I B i i I A
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Performing crosses <ul><li>2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A? </li></ul><ul><li>P 1 I A I B x ii </li></ul>I A I B i I B i i I A I A i I A i I B i I B i
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Performing crosses <ul><li>2. A man with type AB blood and a woman with type O blood have a child. What is the probability that this child will be type A? </li></ul><ul><li>P 1 I A I B x ii </li></ul>I A I B i I B i i I A F 1 Results: ½ I A i – type A blood ½ I B i – type B blood The probability of type A is 50% or 1:2 I A i I A i I B i I B i
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Sex Chromosomes <ul><li>The X and Y chromosomes control gender. </li></ul><ul><li>Females have XX while males have XY. </li></ul>
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Sex Linkage <ul><li>Sex linked genes are found on the sex chromosomes. They are usually on the X. </li></ul><ul><li>Colour blindness and hemophilia are two examples of sex linked genetics. </li></ul>
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Colourblindness <ul><li>X B = normal vision </li></ul><ul><li>X b = colourblindness </li></ul><ul><li>X B X B = normal female </li></ul><ul><li>X B X b = female carrier </li></ul><ul><li>X b X b = colourblind female </li></ul><ul><li>X B Y = normal male </li></ul><ul><li>X b Y = colourblind male </li></ul>
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Hemophilia <ul><li>X H = normal blood clotting </li></ul><ul><li>X h = hemophilia </li></ul><ul><li>X H X H = normal female </li></ul><ul><li>X H X h = female carrier </li></ul><ul><li>X h X h = hemophiliac female </li></ul><ul><li>X H Y = normal male </li></ul><ul><li>X h Y = hemophiliac male </li></ul>
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Performing crosses <ul><li>3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind? </li></ul>
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Performing crosses <ul><li>3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind? </li></ul><ul><li>P 1 X b Y x X B X b </li></ul>X b Y X B X b
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Performing crosses <ul><li>3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind? </li></ul><ul><li>P 1 X b Y x X B X b </li></ul>X b Y X B X b X b Y X B X b
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Performing crosses <ul><li>3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind? </li></ul><ul><li>P 1 X b Y x X B X b </li></ul>X b Y X B X b X b Y X B X b X B X b X b X b X B Y X b Y
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Performing crosses <ul><li>3. A man with colourblindness and a woman who is a carrier have a male child. What is the probability that this child will be colourblind? </li></ul><ul><li>P 1 X b Y x X B X b </li></ul>X b Y X B F 1 Results: ¼ X B X b – carrier normal female ¼ X b X b – colourblind female ¼ X B Y – normal male ¼ X b Y – colourblind male The probability of colourblindness in the male child is 50% or 1:2 X b X b Y X B X b X B X b X b X b X B Y X b Y
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