Genetics Unit Outcomes

Transcription

1 Genetics Unit Outcomes In the cell division unit, you learned that chromosomes come in pairs and that humans have 46 chromosomes in each of their body cells. You receive one of each chromosome from dad and one of each chromosome from mom. Those chromosomes use molecules of DNA to store information called genes. How DNA stores information is something we will talk about in the following unit. You have approximately 30,000 genes for all of your physical traits eye color, hair color, blood type, height, even risk for cancer. What happens if the gene for eye color that you receive from mom (blue eyes) is different from the eye color gene you receive from dad (brown eyes)? Do you have one blue eye and one brown eye? Is each eye a mix of blue and brown? Or does one color win? In this unit, you will learn how to solve genetics problems like this. You will also learn how to predict the chances of certain traits for your kids (offspring). Finally, you will learn how genetic scientists keep track of traits using family trees (pedigrees) to learn how different genes are passed from one generation to the next. If you practice the problem solving steps that we learn, you will have great success in the genetics unit. Upon completion of this unit, the learner will: 1. Apply genetic terminology while solving five types of genetics problems. 2. Predict the genotypes of organisms within a pedigree. Vocabulary genetics heterozygous probability chromosome hybrid punnett square gene homozygous dominant monohybrid dominant homozygous recessive dihybrid recessive pedigree parental generation homozygous genotype F 1 generation purebred phenotype F 2 generation GENETICS UNIT NOTES KRITSCH 1

2 INSERT CALENDAR HERE GENETICS UNIT NOTES KRITSCH 2

3 Monohybrid Lecture We have just spent the better part of a week determining how to apply our prior knowledge about DNA, meiosis, and fertilization to develop a diagram of how traits are passed from one generation to the next. We can simplify this process a bit, by using Punnett Squares. FACTS TO UNDERSTAND 1. Genes can be represented by letters. (GENES ARE PIECES OF CHROMOSOMES THAT CODE FOR A TRAIT) 2. Some traits are dominant. Dominant Note dominant does not mean that they are the most common traits. We will learn in the genetic disorder unit about some traits that are dominant and lethal (i.e. deadly). Understandably, there aren t many people who have lethal, dominant genes. 3. A recessive gene gets a lower case letter of the Dominant Gene. Recessive Note recessive doesn t mean least common. See above. 4. Genes must exist in pairs to express a trait. GENETICS UNIT NOTES KRITSCH 3

4 Example: Purple stems are dominant over green stems. Hint Try to choose the letter of the adjective describing the noun being discussed. What letter should be chosen? What letter should represent purple stems? What letter should represent green stems? Example: Green leaves are dominant over yellow leaves. What letter should be chosen? What letter should represent green leaves? What letter should represent yellow leaves? More terms Homozygous Purebred GENETICS UNIT NOTES KRITSCH 4

5 Heterozygous Hybrid Example: A plant that is homozygous purple stem would have which letters? What letters would a plant that is hybrid for purple stem have? More important terminology: Genotype Phenotype Probability Monohybrid Allele - GENETICS UNIT NOTES KRITSCH 5

6 Hints to solve genetics problems: 1. Decide which trait is dominant and recessive. 2. Choose the correct letters to represent the genes. 3. Decide the genotype of each parent. 4. Decide what genes are in the egg and sperm. 5. Put egg and sperm around the Punnett Square. 6. Combine egg and sperm genes inside Punnett Square. 7. A completed Punnett Square gives the possibilities each time offspring are produced and supplies info asked for. Example: Brown eyes are dominant to blue eyes. Cross a hybrid brown-eyed male with a heterozygous brown-eyed female Dad = Mom = 4. GENETICS UNIT NOTES KRITSCH 6

7 5. & a. What is the chance of an offspring having a child with brown eyes? b. What is the chance of an offspring being hybrid? c. How many genotypes exist? What are they? d. How many phenotypes exist? What are they? GENETICS UNIT NOTES KRITSCH 7

8 Example: Six fingers are dominant to five fingers. Cross a heterozygous six-fingered male with a homozygous five-fingered female Dad = Mom = & What is the chance that this couple will produce a six-fingered baby? GENETICS UNIT NOTES KRITSCH 8

9 Example: Cross a purebred short female plant with a hybrid tall male plant. (NOTE: Plants are often male and female so just choose a gender for a plant if you aren t given one) Dad = Mom = & What is the chance that the offspring will be short? GENETICS UNIT NOTES KRITSCH 9

10 Blood Type Genetics Co-Dominance So far we have been working with traits that are usually either/or situations. Tall or short, green or yellow. Sometimes there are more then two choices. Human eye color is one example of this. Human blood type is another example. There are many different ways that we type blood. Today, we ll look at two systems, ABO and the Rh - factor. ABO Typing: Each red blood cell has proteins on its surface that let the body identify it as belonging to yourself. Blood Type Antigen A Antigen B Antibody anti-a Antibody Anti-B A yes no no yes B no yes yes no O no no yes yes AB yes yes no no Genes A and B are genes. Gene o is the gene. Sample Problem: Mom is hybrid type B blood, Dad is hybrid type A blood. Perform the seven step process. 1. Dominant = A and B Recessive = o 2. A = blood type A B = blood type B o = blood type O GENETICS UNIT NOTES KRITSCH 10

11 5. & Chance of Each Blood Type: Rh Factor Blood Type Rh + means that Rh - means that The dominant gene is The recessive gene is Let s assign letters for each genotype: Phenotype Rh + Rh - Genotype Try This: Dad is heterozygous Rh + factor and mom is homozygous for Rh - factor blood GENETICS UNIT NOTES KRITSCH 11

12 5. & Chance of each blood type Does this type of problem remind you of a type you ve already done? Note: There is a danger if a mom with Rh - blood has a Rh + fetus in her body her antibodies may attack the fetus and cause her to be sick or die. This condition is called erythroblastosis fetalis. If untreated, this can result in the death of the fetus. This shows that it is really important to know your blood type for transfusions as well as pregnancy. GENETICS UNIT NOTES KRITSCH 12

13 Sex Linked Traits Lecture The study of inheritance of genes located on sex chromosomes was pioneered by T. H. Morgan at the beginning of the 20th century. Although Morgan studied fruit flies, the same principles apply to humans. Since males and females differ in their sex chromosomes, the inheritance of X-chromosome linked genes vary between the sexes. What are sex chromosomes? What are sex-linked traits? Which sex chromosome is home of the most sex-linked traits? What are examples of traits that are sex-linked? 1) Color blindness (red-green) 2) Hemophilia 3) Muscular Dystrophy 4) Male pattern baldness What letters should we use to designate these normal and mutant traits? B = b = H = h = M = m = P = p = How should we write these genotypes to help us remember they are sex-linked? Color Vision Genotypes Color Vision Phenotypes X B X B GENETICS UNIT NOTES KRITSCH 13

14 Complete this chart: Genotypes Phenotypes Normal Vision Female Normal Vision Male X m X m Male with hemophilia X H X h Try This: A normal man and a woman with hemophilia plan on having a family & Chance of Normal Chance of Carrier Chance of Hemophiliac GENETICS UNIT NOTES KRITSCH 14

15 Incomplete Dominance Lecture Sometimes genes that are present do not completely dominate the gene they pair with. In these cases the end result is a blend of the two phenotypes. All genes in these problems are dominant. Therefore, only capital letters will be used. Example: Some species of flowers when you cross a red petal and a white petal produce a pink petal. These genes are represented with capital letters. (i.e. Red = and White = Possible genotypes are: Red = White = Pink = Sample problem: Cross a male red flower with a female pink flower using the seven steps we have used before & What are the chances for the offspring to be: a. Red? b. White? c. Pink? GENETICS UNIT NOTES KRITSCH 15

16 Pedigree Lecture A. Pedigree B. Sample Pedigree P F 1 F 2 C. Define the following: I. = P generation = II. = F 1 generation = III. = F 2 generation = D. Pedigree symbols Female Male Marriage or mating line Death Hybrid individual Carrier female Fraternal twins Identical twins GENETICS UNIT NOTES KRITSCH 16

17 Dihybrid Lecture 1. Dihybrid definition Given: B = BROWN; b = BLUE; T = TALL; t = SHORT 2. a. BbTt = phenotype b. Bbtt = phenotype c. bbtt = phenotype d. bbtt = phenotype 3. Sperm contains genes (how many?) 4. Egg contains genes (how many?) 5. In order to predict what could be in the sperm or egg of an organism with genes BbTt, we have to use the ARROW RULE. B b T t 6. What sex cells could be obtained from the genotypes below? Bbtt:,,, bbtt:,,, bbtt:,,, GENETICS UNIT NOTES KRITSCH 17

18 NEW RULE 7. Identical genotypes in sex cells do not have to be repeated. Example: Make a cross between a totally heterozygous brown-eyed tall girl and a heterozygous brown-eyed, homozygous tall guy. 1. Dominant = + Recessive = + 2. Letters =, =, 3. Dad = Mom = & 6. Punnett Square 7. List different phenotypes in the offspring and determine the chances for each type. GENETICS UNIT NOTES KRITSCH 18

19 Multiple Genes Lecture For many traits there are two or more genes the produce variations of one trait. For example, 6 pairs of genes, determine one s skin color. This results in 4,096 different genotypes of skin color. Example: The redness of some wheat kernels seems to be determined by two pairs of genes acting in an additive way. 1. Four dominant genes produce very, dark red kernels. 2. Three dominant genes produce dark red kernels. 3. Two dominant genes produce a medium red kernel. 4. One dominant gene produces a light red kernel. 5. A lack of any dominant genes produces a white kernel. If R and S are genes related to the redness of wheat kernels (r and s represent the lack of redness) what will the phenotypes of each of the following genotypes be? RrSs RRss RrSS rrss Rrss RRSS Give the different genotype combinations that could be present in each of the above genotypes: (Hint: The arrow rule) Cross medium red wheat (RrSs) with dark red wheat (RrSS) /6. 7. GENETICS UNIT NOTES KRITSCH 19