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Genetics

Unit 9. Genetics. What is Genetics?. Genetics is the study of heredity. Heredity is how traits are passes down from generation to generation. “Father of Genetics”. He studied the way characteristics are passed on in pea plants in the 1800’s. Gregor Mendel. Mendel’s Discovery.

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Genetics

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  1. Unit 9 Genetics

  2. What is Genetics? Genetics is the study of heredity. Heredity is how traits are passes down from generation to generation. “Father of Genetics”. He studied the way characteristics are passed on in pea plants in the 1800’s. Gregor Mendel

  3. Mendel’s Discovery • Mendel discovered that a pea plant’s characteristics such as height, seed color and pod color are determined by an inheritance factor. • These inheritance factors where later called genes. Genes are a unit of heredity. They contain the instructions for a trait. • A trait is a characteristic (color, height) coded for by two or more genes.

  4. Genes A gene can be defined as a region of DNA that controls a hereditary characteristic. Genes can be as short as 1000 base pairs or as long as several hundred thousand base pairs. It can even be carried by more than one chromosome. The estimate for the number of genes in humans has decreased as our knowledge has increased. As of 2001, humans are thought to have between 30,000 and 40,000 genes. http://www.accessexcellence.org/RC/VL/GG/genes.html Chromosomes Genes DNA

  5. Cell nucleus containing 23 pairs of chromosomes genes chromosomes DNA strand DNA makes up genes. Genes make up chromosomes. There are 23 pairs (46 total) chromosomes in each non-sex cell for humans. 23 chromosomes in sex cells.

  6. http://www.accessexcellence.org/RC/VL/GG/human.html Females have XX chromosomes. Males have XY chromosomes. Genetic disorders: Tay-Sachs: Caused by a gene mutation on chromosome 15 Down Syndrome: An extra copy of chromosome 21 is present. Look up other genetic disorders.

  7. Types of Genes Allele: 2 forms of a gene Dominant: The gene that covers up the effect of the other one. Use a capital letter. Mendel’s Experiment: Green seed color(G) Recessive: The effect of the gene is hidden (unless two are present). Use a lower case letter. Mendel’s Experiment: Yellow seed color (g)

  8. Describing Genes When we write genes we use one letter (G or g, R or r, etc.) Traits or characteristics are determined by one or more pair of genes. Half of your genes come from your mother and half of your genes come from your father. Homozygous or purebred: Both genes are the same. Mendel’s Experiment: Green seed color(GG), Yellow seed color (gg) homozygous dominant,homozygous recessive Heterozygous or hybrid: Both genes are different. Mendel’s Experiment: Green seed color(Gg)

  9. Describing Traits Traits are ways to describe living things. We are going to focus on human traits during genetics. Traits that we may discuss include: hair color, eye color, blood type. Phenotype: What the organism looks like. Mendel’s Experiment: Green seed color, Yellow seed color Genotype: The genetic make-up of a trait. Mendel’s Experiment: GG, Gg or gg

  10. Practice Problem Mendel also studied the heights of pea plants during his experiments. He determined that tall pea plants were dominant over short pea plants. Step 1: Create a key. Pick a letter to represent genes. Dominant = Tall (T) Recessive = short (t) Use the key to help you answer the following questions: 1. Determine the phenotype of a plant that is Tt. 2. Determine the genotype of a homozygoussmall plant. 3. Would a heterozygous plant show the dominant or recessive trait?

  11. Dominant = Tall (T) • Recessive = short (t) • Determine the phenotype of a plant that is Tt. • Phenotype means what it looks like. It will be tall because it has one dominant gene (T). • 2. Determine the genotype of a homozygoussmall plant. • Genotype means genetic make-up. Homozygous means the same and small is recessive (small letter).The answer is tt. • 3. Would a heterozygous plant show the dominant or recessive trait? • Heterozygous means different. (Tt) The answer is dominant because there is at least one big T. To show recessive you have to have two small t’s.

  12. Cell Division • Mitosis: • Occurs in body cells. • One cell divides into two. • Both cells have the same genetic material as the parent cell. Four chromosomes Four chromosomes copied Four chromosomes go into each cell during division Four chromosomes in each identical cell

  13. Cell Division • Meiosis: • Occurs in sex cells (egg and sperm). • One cell divides into four. • The four daughter cells have ½ the genetic material as the parent cell. Stage 1: Stage 2:

  14. Vocabulary Practice Problems 1. Brown hair is dominant over blonde. A. Create a key for the traits. B. What would the genotype for a blonde be? C. What would the phenotype be for a person that is heterozygous? 2. Freckles is dominant over non-freckles. Mom is purebred for freckles. Dad is heterozygous for freckles. A. Create a key for the traits. B. Determine the genotypes for Mom and Dad. C. Could any of their children NOT have freckles? Explain your answer.

  15. 1A. Key: B = brown = dominant b = blonde = recessive 1B. Blonde is recessive. “bb” 1C. Heterozygous means different. Phenotype means what it looks like. “Brown hair” 2A. Key: F = freckles = dominant f = non-freckles = recessive 2B. Mom = FF Dad = Ff 2C. There is no possibility that any of their children could not have freckles. Mom has two big F genes, which means she will always give her children a F. Therefore all of the children will have freckles. You need two little f’s for non-freckles.

  16. Pedigree Chart Follows the passing of a trait from generation to generation. Looks like a family tree. = male = female Shaded shape means that the recessive trait is expressed. Half shaded shape means that they are a carrier of the trait. Carriers have one gene but do not express or show the trait.

  17. marriage Generation 1 parents Generation 2 children Oldest child to the left Youngest child to the right Number of rows = number of generations Count from the top to the bottom

  18. N = normal vision = dominant n = nearsighted = recessive Shaded = recessive trait 1 2 nn N _ 4 3 N n nn 9 8 6 7 5 nn nn N n nn N n 11 12 10 Page 6 in Packet nn N n N n

  19. More Pedigree Practice D = dimples d = non-dimples 1 2 Dd dd 3 4 5 6 7 Dd dd Dd dd Dd 8 9 10 12 14 15 11 13 Dd dd dd dd dd Dd Dd Dd

  20. Punnett Squares Determine the probability that offspring will or will not have a given trait. Think back to Mendel’s pea experiment. We looked at green seeds and yellow seeds. If both plants are homozygous, what are their genotypes? Plant 1 (green) = GG Plant 2 (yellow) = gg Identify the genes that are present in each plants’ sex cells. GG gg G G g g

  21. We are now going to determine the possible genotypes and phenotypes of the offspring using a Punnett Square. GG x gg Genotype g g gg = 0/4 = 0% Gg = 4/4 = 100% Gg Gg G GG = 0/4 = 0% Phenotype Gg Gg Green = 4/4 = 100% G Yellow = 0/4 = 0%

  22. Determine the genotype and phenotype probabilities for a cross between two heterozygous plants from the previous problem. Parents = Gg X Gg Genotype G g gg = 1/4 = 25% Gg = 2/4 = 50% GG Gg G GG = 1/4 = 25% Phenotype Green = 3/4 = 75% Gg gg Yellow = 1/4 = 25% g

  23. Determine the genotype and phenotype probabilities for a cross between a heterozygous plant and a short plant. The trait we are studying is plant height. Tall is dominant over short. Parents = Tt X tt T = tall = dominant t = short = recessive Genotype T t TT = 0/4 = 0% Tt = 2/4 = 50% t Tt tt tt = 2/4 = 50% Phenotype Tall = 2/4 = 50% t tt Tt Short = 2/4 = 50%

  24. Punnett Square Practice Problems • Normal skin pigment is dominant over albino. Show a cross of an albino man with a heterozygous normal woman. • Brown eyes are dominant over blue eyes. Using a Punnett Square, determine the probability that the offspring will be homozygous recessive if both parents are heterozygous dominant. • Determine the genotypes for the individuals in the pedigree chart below. Widow’s peak is dominant over non-peak. • Make a key • Determine genotypes • Determine number of generations • What is the dominant trait? • How many males have peak? • How many marriages?

  25. 1. Key: N = normal = dominant n = albino = recessive Parents: Male = nn Female = Nn n n Genotype NN= 0/4 = 0% Nn Nn = 2/4 = 50% N Nn nn = 2/4 = 50% Phenotype normal = 2/4 = 50% n nn nn albino = 2/4 = 50%

  26. 2. Key: B = brown = dominant b = blue = recessive Parents: Male = Bb Female = Bb B b Genotype BB= 1/4 = 25% Bb Bb = 2/4 = 50% B BB bb = 1/4 = 25% Phenotype brown = 3/4 = 75% b Bb bb blue = 1/4 = 25%

  27. I II III IV Key: W= widow’s peak = dominant w = non- peak = recessive Ww Ww Ww Ww W_ W_ ww Ww W_ ww W_ Ww W_ ww c) 4 generations d) Having the widow’s peak is dominant. e) 2 males have a widow’s peak. f) 4 marriages Ww

  28. Sex-linked traits • Sex-linked traits are caused by genes found on the X chromosome. • Sex-linked traits are recessive. • Fewer females are afflicted with these traits because they have two X chromosomes and the other is usually normal. • Males only have one X chromosome, so when they inherit the sex-linked gene, they display the trait. • Examples: color-blindness, hemophilia XX XX- X-X- XY X-Y Normal female Carrier female Afflicted female Normal male Afflicted male

  29. Sex-linked traits practice problems • A man normal for blood clotting marries a woman who is a carrier for hemophilia. What are the chances they will have a child with hemophilia? Use a Punnett Square to prove your answer. • What is the probability that a woman with normal vision who marries a color-blind man will have a color-blind child? • A man with normal vision and a woman with normal vision have three sons. Two of the sons have normal vision and one of them is color-blind. What are the probable genotypes of the parents?

  30. Intermediate Inheritance • Not all traits are either dominant or recessive. • For some traits, heterozygous individuals are different than both homozygous parents. Codominance Incomplete Dominance • Both alleles are blended in heterozygous offspring • Both are different capital letters • Both alleles are expressed in heterozygous offspring • Both alleles are dominant • Both are different capital letters Red flowers = RR White flowers = WW Pink flowers = RW Red coat = CR CR White coat = CW CW Roan coat = CR CW (both red and white are seen)

  31. Multiple Alleles: • When there are more than 2 (multiple) alleles for a trait. • Examples: Human blood groups have 3 alleles. (A, B, O) • A and B are both dominant, O is recessive • The possible combinations of these blood alleles are:

  32. tb TB Dihybrid Crosses • Study two traits at the same time. • Determine the outcome for both traits together. A pure tall plant with blue flowers is mated with a short plant with white flowers. Determine the genotypes and phenotypes of the offspring. Tall and blue flowers are both dominant traits. TTBB X ttbb Parents: T = tall ttbb TTBB t = short tb TB B = blue b = white

  33. tb tb TB TB TtBb TtBb TtBb TtBb Genotype Phenotype Tall and blue = 100% TtBb = 100%

  34. TB TB Tb Tb tB tB tb tb Now mate two of the offspring to determine the possible genotypes and phenotypes. Genotype TtBb X TtBb ttbb = 1/16 = 6.25% ttBb = 2/16 = 12.5% TB Tb tB tb ttBB = 1/16 = 6.25% Ttbb = 2/16 = 12.5% TB TTBB TTBb TtBB TtBb TtBb = 4/16 = 25% TtBB = 2/16 =12.5% Tb TTBb TTbb TtBb Ttbb TTbb = 1/16 = 6.25% TTBb = 2/16 = 12.5% TTBB = 1/16 = 6.25% tB TtBB TtBb ttBB ttBb Phenotype Tall, blue = 9/16 (56.25%) Short, blue = 3/16 (18.75%) Tall, white = 3/16 (18.75%) Short, white = 1/16 (6.25%) tb TtBb Ttbb ttBb ttbb

  35. Incomplete dominance & Codominance • When a mouse with black fur is crossed with a mouse with white fur, all F1 generation offspring have gray fur. What are the probable genotypes and phenotypes for the F2 generation? Is this an example of codominance or incomplete dominance? • What would the possible genotypes and phenotypes be for a cross between a roan-coated cow (CR CW) and a red-coated cow (CR CR)? Is this an example of codominance or incomplete dominance?

  36. Blood Type Problems • A couple preparing for marriage have their blood typed. They are both AB. They are curious about the possible blood types their children might have. What are the possible phenotypes of their children? • A type A person marries a type A person. Their firstborn has type O blood. What are the genotypes of the parents and the child? • A wealthy elderly couple die together in an accident. Soon a man shows up to claim their fortune, claiming he is their long lost son. Other relatives dispute the claim. Hospital records show that the deceased couple were blood types AB and O. The person claiming to be their son is type O. Do you think this man is an impostor? Explain why.

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