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1 7th Grade PSI Inheritance and Variation of Traits 20151102 www.njctl.org 2 Table of Contents: Inheritance and Variation of Traits Click on the topic to go to that section • Mendelian Genetics • Using Punnett Squares • Test Crosses • Genetic Mutations 3 Mendelian Genetics Return to Table of Contents 4 Heredity Did you ever notice how much children look like their parents and their siblings? As you can see, it's not only something that happens in humans! This is true about all living things on Earth. 5 Frequently Asked Questions I am sure that questions like these have crossed your mind before: • Are children ever identical to their parents? • Why do some people look more like their dad and some look more like their mom? • How do I get traits from my parents? • Why are some people born with birth defects or diseases? These questions (and more) will be answered in this unit! 6 Genetics & Heredity Here are two related terms that will show up quite a few times in this section. Try to define them with your table and then pull the tab for the definition: Answer Genetics Heredity 7 Review: Cells Earlier this year, we talked about the parts of the cell. We also talked about mitosis and meiosis and how these processes help organisms live and reproduce. 8 Review: Mitosis Mitosis is the process that helps individual cells reproduce. In mitosis, one "parent cell" reproduces its DNA and then splits into two identical "daughter cells". The daughter cells are completely identical to the parent cell. The Stages: Permission Granted: Jeff Sale San Diego St Univ 9 Review: Meiosis Meiosis occurs in all animals that reproduce sexually (2 parents). In meiosis, the cell splits in two individual sex cells without duplicating its DNA.This means that after meiosis, the sex cells have half of the DNA as a normal body cell. The human cell on the left has all 23 After meiosis, the pairs of pairs of chromosomes (one pair is chromosomes split. shown). This means that each sex cell ends Click on the cell to see what happens up with 23 individual chromosomes after meiosis! (1/2 of what they started with)! 10 1 Where is all of the genetic information (DNA) found in the cell? B cytoplasm Answer A nucleus C cell membrane D mitochondria 11 2 The process of creating new cells from existing cells is called mitosis. False Answer True 12 3 The purpose of mitosis is _______________. A growth of organisms C both A and B are true Answer B repair of damaged tissue D Neither A nor B are true 13 Answer 4 Each cell in the human body has 23 pairs of chromosomes. How many chromosomes total will each daughter cell have after mitosis? 14 Answer 5 Each cell in the human body has 23 pairs of chromosomes. How many chromosomes total will each sex cell have after mitosis? 23 to 15 6 Meiosis leads to: B Genetic Variation C Cloning Answer A Four offspring cells D Both A and B are true E A, B, and C are true 16 7 After meiosis, the number of chromosomes is the same in the parent and offspring cells. False Answer True 17 Gregor Mendel In the 1800s, an Austrian monk named Gregor Mendel conducted a series of experiments that were designed to uncover how traits are passed on from parent to offspring. His experiments were aimed at addressing one of the most fundamental issues concerning heredity: What are the basic patterns of heredity? 18 Two Prevailing Original Hypotheses At Mendel's time, there were 2 popular (and incorrect) ideas to explain heredity: 1. The “blending” hypothesis : This idea stated that genetic material from the two parents blends together ex: a red flower and a white flower will produce a pink flower 19 Two Prevailing Original Hypotheses 2. Inheritance of mutations: This idea stated that traits present in parents are modified as they are used or not used, and passed on to their offspring in the modified form. ex: A giraffe has a long neck because her parents kept stretching their own necks out to reach the leaves in the trees, and the long neck trait was passed on. 20 Mendel's Experiments In order to complete his experiment, Mendel needed to choose an organism that had the following characteristics: Usually small Has a short life span Inexpensive to take care of Produce many offspring in a relatively short period of time Easy to experiment with Why do you think these traits would be important to scientists? Talk about each one at your table and be prepared to share your thoughts. 21 Mendel's Experiments How many living things can you think of that fulfill these guidelines? Make a list with the person sitting next to you. Click below to see what Mendel chose to work with. The garden pea 22 Mendel's Choice: The Pea Plant Mendel chose pea plants for his experiment because: • There are many varieties with distinct traits (such as color). • He could easily control the matings through crosspollination. • Each pea plant has both the male and female reproductive organs. 23 The Traits of Pea Plants Mendel chose to track 7 traits (or "observable characteristics") that only came in one of two forms. 24 8 Pea plants were particularly a good choice for use in Mendel's experiments for all of the following reasons except that... B It is possible to completely control matings between different pea plants. Answer A Peas show easily observed variations in a number of characters, such as pea shape and flower color. C It is possible to obtain large numbers of offspring from one cross. D Peas live for an unusually long time. 25 Experiment #1: Monohybrid Cross One of Mendel's experiments looked at flower color. A pea plant can either have purple or white flowers. For this experiment, he crossed a purple flower with a white one. This is called a monohybrid cross because the parent plants differ in only one trait, their flower color. Results: All of the offspring had purple flowers. "mono" = one 26 Monohybrid Cross Mendel then mated two of the purple offspring plants. This cross produced 929 plants. Use a calculator What percentage of these flowers were purple? Answer Results: 705 of the 929 plants had purple flowers and 224 had white flowers _____________________% 27 Monohybrid Cross Can you make any conclusions based on these results? Write any ideas below. Think about the Blending Hypothesis. Does this experiment support or disprove this hypothesis. Why? 28 Interpreting Mendel's Results Based on the results from this experiment, Mendel concluded that the trait for white flowers did not disappear in the purple plants, but instead that the purplecolor factor was controlling the flower color. He also concluded that these plants must have carried two factors for the flowercolor character: one represented purple and one represented white. 29 9 A genetic cross in which the parents differ in only one trait is known as a ___ cross. B dihybrid C self Answer A monohybrid D test 30 Webquest: Mendel's Peas This lab will have you try out some of Gregor Mendel's experiments on genetics and heredity. By the end of this webquest, you will have an idea of the different patterns of inheritance he saw in his experiments. Click on the picture above to access the website! 31 Alleles From Mendel's experiments, he came up with a few ideas that reshaped the study of genetics. His first idea was that genes come in different forms. This causes organisms of the same species to still have some differences. For example, the pictures above show that the human eye can look a variety of different ways, such as being blue or brown. 32 Alleles There is a variation of the gene for flower color in pea plants that can cause it to be purple. Another variation makes it white. The alternative forms of genes are called alleles. 33 The Passing on of Alleles Looking at his experiments, Mendel also concluded that an organism inherits two alleles (one from each parent) for each trait. The two alleles may be the same or they may be different. These alleles will pair up in the child and will determine what the child's physical traits are. Mother Father Represents an allele 34 Homozygous Organisms Each allele can be represented with either a capital or lowercase letter. An organism that has two of the same alleles (i.e two identical letters) for a gene is homozygous for that gene. Examples: Two capital letters (AA) Two lowercase letters (aa) "homo" = the same 35 Heterozygous Organisms An organism that has two different alleles (i.e two different letters) for a gene is heterozygous for that gene. Example: One capital and one lowercase letter (Aa) "hetero" = different 36 Dominant and Recessive Alleles If the two alleles of a pair are different (heterozygous), one allele determines the physical appearance and is called the dominant allele. The other allele has no noticeable effect on the appearance and is called the recessive allele. Memory Tactic: The dominant allele dominates the recessive one. 37 Dominant and Recessive Alleles In other words, Mendel came up with the idea that one variation of the trait will be shown. If one parent has blue eyes and one has brown eyes, the child would more than likely end up with one or the other, as opposed to something like this: 38 Dominant and Recessive Alleles This hypothesis also went against the "blending hypothesis" from before. How did that hypothesis work? ? According to Mendel's hypothesis, if the two variations are red and white, then the offspring will either show the red or white trait only. 39 Describing Traits We can describe a trait in terms of the physical appearance of that trait or the alleles present for a trait. For example, suppose we are looking at the pea plant below. We can either say that it has purple flowers or that its alleles for the flower color trait are Pp. 40 Phenotype vs Genotype When you describe the physical appearance of a trait, you are describing its phenotype. When you describe the alleles of a trait, you are describing its genotype. Phenotype: purple flowers Genotype: Pp 41 Phenotype vs Genotype In humans, there is a gene for eye color. The brown eye gene (B) is dominant to the blue eye gene (b). Suppose that you meet someone who is homozygous dominant for this gene. What is their genotype and phenotype? Click in the boxes to check your answers. Genotype Phenotype BB brown eyes 42 Law of Segregation A sex cell carries only one allele for each trait because allele pairs separate (or segregate) from each other during meiosis and go into separate cells. This is known as The Law of Segregation. rehtaF rehtoM This means that the parent can't "accidentally" pass on two of the same chromosome. 43 10 Alternate versions of a gene are called ___. A chromatids C heterozygotes D alleles Answer B heritable factors 44 11 An organism that has two identical alleles for a gene is said to be ___ for that gene. A dominant C homozygous Answer B recessive D heterozygous 45 Using Punnett Squares Return to Table of Contents 46 The Law of Segregation We just discussed Mendel's Law of Segregation. Use the space below to explain it in your own words. rehtaF rehtoM 47 Punnett Square The possible combinations of sperm and egg (the human sex cells) can be shown using a Punnett square. A Punnett square is a diagram for predicting the results of a genetic cross between two individuals. ? In order to understand how our Punnett Square will look, we need to figure out how many possible combinations of alleles there can be. 48 Answer 12 According to Gregor Mendel, how many alleles did an organism have for each trait? 49 Setting Up a Punnett Square All organisms have two alleles for each characteristic and passes one of these on to the offspring (remember the Law of Segregation!). Parent's Cell ____chromosomes The image on the right demonstrates this as seen in humans. Fill in the blanks to note the number of chromosomes in the parent and sex cells. Sex Cells reh____ taF chromosomes rehtoM 50 Combinations In order to find out the possible number of combinations, let's picture it in a different situation: clothing. Below, you see four pieces of clothing. Make as many different combinations of shirts and pants as you can! A B Place combinations here. Pants Shirts 51 Combinations On the page before, we had 2 possible types of shirts (A and B) and 2 possible types of pants (purple and black). We discovered from our activity that there are 4 possible combinations of these pieces of clothing. A A B B Creating each possible combination is fine when the numbers are small, but what about when this would not be practical? 52 The Counting Principle If there are A number of options for one object and there are B number of options for a second object, then the total number of combinations of the two is: A x B So in our example, there were 2 types of shirts and 2 types of pants. The total number of combinations of shirts and pants will be: 2 x 2 = 4 53 Answer 13 Mindy is at the ice cream parlor. There are 6 different flavors of ice cream and 4 different types of cones. How many different types of ice cream cones can she make? 54 How many different sandwiches could he make using one type of bread, one meat, and one cheese? Answer 14 Steven is making a sandwich. When he opens the refrigerator, he sees 2 different types of breads, 5 different types of meat and 2 different types of cheese. 2 55 Back to the Punnett Square... Since the mother can pass on 2 alleles and the father can pass on 2 alleles, there are 4 potential combinations. (2 x 2 = 4) Therefore, our Punnett Square is going to consist of 4 boxes: 56 Dominant and Recessive Traits As Mendel said, alleles come in two different forms: dominant or recessive. Mendel represented these different traits with either a capital or a lowercase letter. An uppercase letter represents a dominant allele, and a lowercase letter represents a recessive allele. A a Dominant Recessive We will be using these letters in our Punnett Square. 57 Genotype In order to set up our Punnett Square, we need to know what the parents' genotypes are. The "genotype" is what the person's genes, or DNA, look like. A person's genotype determines what trait they have and what visible trait you will see! For our sample Punnett Square, let's give the parents the following genotypes: Father Mother AA Aa Memory Tactic: The "genotype" tells you what the "genes" look like 58 Setting Up a Punnett Square A Punnett Square works like a data table; information will be put on the top of the table and on the left of the table. We will put one parent's genotype on the top (in this case, the mother's) and the genotype of the other parent (the father) will go on the left. Mother's Genotype Father's Genotype 59 Setting Up a Punnett Square Click on the boxes to uncover the components of the Punnett Square: Mother's Genotype A a A Father's Genotype A 60 Setting Up a Punnett Square Click on the boxes to uncover the components of the Punnett Square: Mother's Genotype A a A AA Aa A AA Aa Father's Genotype The genotypes in the Punnett Square represent the possible combinations that the offspring could have. The offspring can only be either be AA or Aa. 61 A Homozygous Dominant B Homozygous Recessive C Heterozygous D Heterozygous Dominant Answer 15 Two of the four boxes contained "AA." Which term below accurately describes this genotype? 62 A Homozygous Dominant B Homozygous Recessive C Heterozygous D Heterozygous Dominant Answer 16 The other two boxes contained "Aa." Which term below accurately describes this genotype? 63 Phenotype We have already learned that "genotype" is what the genes look like. The "phenotypes" of an organism are the observable characteristics, the organism's physical traits. The phenotypes are based on the genotypes and can be seen very easily. What are some phenotypes of the man to the left? Make a list with your table. 64 Dragon Crossing Activity In this activity, you will be given the task of breeding a special dragon for the king. Use your knowledge of Punnett Squares, genotypes and phenotypes to complete the process! 65 Mendel's Experiments In his experiments, Mendel crossed a homozygous dominant purple flower with a homozygous recessive white flower. Complete the cross: A A a a 66 Heterozygous Genotype The dominant allele shows in the heterozygous flower, while the recessive allele has no effect on flower color. Therefore, a Aa flower has a purple phenotype (purple is dominant). Phenotype Genotype AA Aa Even though the genotypes are different, What do you notice about the phenotypes? 67 Homozygous Recessive Genotype On the flip side, if an organism shows the recessive phenotype, there is only one way their genotype could look: Phenotype Genotype aa The organism HAS to have two recessive alleles. If it has even one dominant allele, what phenotype will it show? 68 A All purple B All white C All pink D 1/2 purple, 1/2 white Answer 17 In Mendel's experiment three slides back, what colors were the offspring flowers? 69 The Next Generation In the next step of Mendel's experiment, he took 2 of the offspring from his first cross and decided to cross them as well: Aa x Aa Set up and complete the cross below: 70 Answer 18 How many flowers in the 2nd generation were purple? 71 Answer 19 Three out of four flowers were purple. What percentage of the flowers were purple? 72 Looking at Genotypes Looking at genotype Father's Genotype A a F1 Generation A AA Aa a Aa aa Mother's Genotype F2 Generation AA Homozygous Dominant We can see that if both the mother and father pass on an A allele, the offspring will be AA and therefore have purple flowers. In this type of cross, this particular genotype (homozygous dominant) will statistically occur in about 1/4 of the offspring. 73 Looking at Genotypes Looking at genotype Father's Genotype A a F1 Generation A AA Aa Mother's Genotype a Aa Aa aa Heterozygous F2 Generation There are two ways in which a heterozygous organism can emerge: Mom passes on A Dad passes on a Mom passes on a Dad passes on A What percent of offspring could have the Aa genotype? What color will their flowers be? 74 Looking at Genotypes Looking at genotype Father's Genotype A a F1 Generation A AA Aa Mother's Genotype aa a Aa aa Homozygous Recessive F2 Generation The remaining 1/4 of the plants will likely inherit an a from both the mother and the father. These plants will have a aa genotype and will be what color? 75 Genotype vs. Phenotype We have already established that the genotype (what the genes look like) determines what the phenotype (the physical traits) will be. In this example, AA and Aa plants had the same phenotype but different genotypes. Phenotype Genotype AA or Aa 76 Genotype vs. Phenotype Complete the chart below for the flowers we have discussed. Genotype Phenotype Purple Purple aa 77 20 Red flowers (R) are dominant to white flowers. According to the chart below, Parent Plant A has what color flowers? B Red White Flower Genotype Parent Plant A Rr Parent Plant B RR Answer A 78 21 Red flowers (R) are dominant to white flowers. According to the chart below, Parent Plant B has what color flowers? Red B White Parent Plant A Rr Parent Plant B RR Answer A Flower Genotype 79 22 The plants below can produce white flowers. A True B False F2 Generation Answer F1 Generation Flower Genotype Parent Plant A Rr Parent Plant B RR 80 Flower Genotype Parent Plant A Rr Parent Plant B RR Answer 23 The probability that the Parent Plants A and B will produce a plant with red flowers is ______%. 81 Jane and John Activity How are traits passed on from parent to offspring? In this activity, you and a partner will be determining the traits of two individuals and will use a Punnett Square to look at the possible genotypes that their child can have! 82 Test Crosses Return to Table of Contents 83 Determining Genotype from Phenotype How can we tell the genotype of an individual with the dominant phenotype? In Mendel's pea plants those with WW or Ww both appeared purple. So if we have a pea plant with purple flowers, how do we determine which genotype the plant has? AA ? Aa ? 84 Test Cross A test cross involves breeding the individual whose genotype we are trying to determine with a homozygous recessive individual. In a test cross, you will always cross an organism that shows the dominant trait with one that shows the recessive trait. Permission Granted: Penn State Dept of Biology 85 Test Cross In a test cross, the unknown genotype is either homozygous dominant or heterozygous. What would the offspring look like if the unknown genotype is homozygous dominant? Complete a punnett square to determine your answer. Click below to check your answer. p p F1 Generation P Pp Pp P Pp Pp All offspring would show the dominant phenotype. F2 Generation 86 Test Cross What would the offspring look like if the unknown genotype is heterozygous? Complete a punnett square to determine your answer. Click below to check your answer. p p F1 Generation P Pp Pp p pp pp Half of the offspring will show the dominant phenotype and half will show the recessive phenotype. F2 Generation 87 Test Cross Results If all offspring display the dominant phenotype, the parent must be homozygous dominant (PP). If any offspring displays the recessive phenotype, the parent must be heterozygous (Pp). Permission Granted: Penn State Dept of Biology 88 A genome B genotype C phenome D phenotype Answer 24 An organism's expressed, or physical, traits are known as its: 89 A hybrid cross. B heterozygous cross. C testcross. D unknown cross. Answer 25 Crossing an individual that is homozygous recessive with an organism of unknown genotype that exhibits a dominant phenotype is known as a ____________. 90 Setting up a Testcross To complete a testcross, you must always cross one organism with the dominant phenotype with one that shows the recessive trait. P = Purple p = white p p F1 Generation In order for the one flower to be white, it must have one particular genotype. This genotype has been added to the Punnett Square to the right. F2 Generation 91 Setting up a Testcross P = Purple p = white As for the other flower, we know it must have at least one dominant allele, which has been added to the Punnett Square on the right. p p F1 Generation P How do we know this must be true? F2 Generation 92 Solving a Testcross p p F1 Generation P ? F2 Generation The other letter is being represented by a "?" because we do not know if it is a "P" or a "p" yet. We need to look at the offspring in order to know what the parent's genotype is. Because of this, we will do two different crosses to see how the offspring will differ. 93 Solving a Testcross We can begin filling in the Punnett Square above with the information we have so far: p p F1 Generation P Pp Pp ? ?p ?p F2 Generation This will help us see what allele we must fill in for the question mark. 94 Pp x pp PP x pp F1 Generation F1 Generation P Pp Pp p p p p P Pp Pp p P F2 Generation F2 Generation _____/4 purple flowers _____/4 purple flowers _____/4 white flowers _____/4 white flowers __________% purple flowers __________% purple flowers __________% white flowers __________% white flowers 95 Testcross Trends The percentages on the prior slide hold true for every testcross: If every offspring shows the dominant trait (100%), the parent with the dominant trait is homozygous dominant (ex. PP). If about half of the children show dominant and the other half show recessive (50% / 50%), the parent with the dominant trait is heterozygous (ex. Pp). FYI: If even one child shows the recessive trait, the parent must be heterozygous. The percentages above only represent the probability. 96 Testcross Activity This activity will allow you to practice setting up and solving testcrosses. At each station will be a different situation. Using the file folder and the sticky note papers, you will set up and solve the testcross. You will then transfer the information to your student worksheet! 97 Genetic Mutations Return to Table of Contents 98 Review: DNA DNA is the blueprint of life. DNA contains ______________ that carries instructions for making proteins that control an organism's life functions. DNA is shaped like a ____________. Each rung of the ladder is made up of compounds. The order of these compounds determines what protein will be made in the cell. 99 Review: DNA DNA can be found in the _____________ of the cell. It plays a vital role in cellular reproduction (which is called _________) and helping the cell survive. 100 Review: Base Pairs DNA is made up of 4 bases: adenine , thymine , guanine , and cytosine . We will refer to them as A T C and G. _____ and _____ always bond together. _____ and _____ always bond together. 101 Review: Protein Synthesis These bases play a role in protein synthesis . During protein synthesis, information from DNA is carried to the ribosomes, where it is used to make proteins out of amino acids. The sequence of genetic information found on the genes determines what kind of protein is made. For example: AAG or TCG Each of the trios above will lead to the creation a different protein. 102 The Role of Proteins Proteins have much more significance than we think! They do most of the work in our cells and are the basis for all of the organs and tissues in our bodies. Proteins are made up of many different subparts known as amino acids . The sequence of letters in our DNA determines what amino acids are made. 103 The Role of Proteins The image to the right may look like a blob, but it is actually a protein known as hemoglobin. This protein is found in our blood and is responsible for carrying oxygen from the blood to the rest of the body! 104 Types of Proteins Antibodies are responsible for getting rid of viruses and bacteria in the body. Enzymes carry out all of the chemical reactions inside of cells. They also help form new molecules by reading the DNA. Messenger proteins, such as hormones, send signals throughout the body to coordinate different things. Some proteins are required for structure and support for cells. They also allow the body to move. Finally, some are responsible for transport and storage of atoms and molecules in the body. 105 Mutations Every cell in your body contains a copy of the same exact DNA. Every so often though, a mutation will occur to alter your genetic blueprint. A T A T A T A T G C T A T A C G C G A T A mutation is a change in the DNA sequence that can reshape your entire genetic code. It could happen as a result of an error in DNA duplication or by the insertion or deletion of genetic code inside the cell. 106 Mutations In the example above, the base pair of G and C was somehow eliminated. This may have happened accidentally through an error during DNA replication or the DNA could have been damaged in some way. As a result, the genetic code changes. What used to read as AAG and TTC before now reads as AAT paired with TTA after. This will result in different proteins being made. 107 The Domino Effect of Genetic Mutations For example, read the sentence below: THE BAD DOG CAN NOT RUN Now let's remove one piece of this sentence (the "A" in "BAD") and move all of the other letters up in its space: THE BDD OGC ANN OTR UN There is a chain effect throughout the rest of the sentence because one piece is missing! 108 Environmental Causes of Mutations There are a few different environmental causes of mutations in human DNA. Some of the most common causes are: Radiation (such as UV radiation from the Sun) Chemicals (such as coming in contact with radioactive waste) Viruses (when viruses attack your cells, they can damage the DNA inside) Although your body has ways of repairing most accidental changes to your DNA, some errors make their way past these checks and become permanent mutations. 109 26 Mutations can happen as a result of exposure to _________. B radioactive chemicals C certain viruses Answer A sunlight D all of the above 110 27 Does your body repair all mutations? Yes Answer No 111 28 Changing one letter in the genetic code can cause a mutation. False Answer True 112 Types of Mutations Genetic information can be altered through an error in DNA replication or from some sort of environmental damage after the baby is born. These are called acquired mutations. If the mutated DNA is present in the sperm or egg cells of an organism, it could then be passed on to the next generation. A mutation that is acquired from one's parents is called a hereditary mutation. Every cell in this organism's body will have the mutated DNA. 113 Are All Mutations Harmful? As was said before, a mutation in one's DNA will alter the proteins that are being coded for in the body. If one or more of these proteins is not functioning properly (or is missing entirely), it can disrupt normal development within the body or can cause a medical condition. These illnesses are known as genetic disorders . Progeria Tuberous Sclerosis 114 Are All Mutations Harmful? On the other hand, there are some genetic mutations that have no negative effect on the body at all and some that are even beneficial! 5 ft 6 ft 2 in This section will look at a number of possible effects of genetic mutations. 115 Mutations Can be Helpful! Sometimes, DNA mutations can cause an organism to be able to survive better in his or her environment. For example, imagine that there is an organism with a genetic mutation that makes it immune to cancer. What types of advantages would this creature have over other organisms in its same species? 116 29 Mutations can occur in DNA _________. A only before a baby is born C only when an organism is exposed to something bad Answer B anytime during an organisms life D only when the pregnant mother does something to cause them 117 30 All mutations are bad. True Answer False 118 Mutations Can be Helpful! There are people out there who have genetic mutations that help them live longer, healthier lives. One realworld example comes to us from a small village in Italy called "Limone sul Garda." Some of the people in this community possess a mutation in a protein in their blood that helps their bodies clean out cholesterol from their veins. Possessing this trait allows the people to eat whatever they want with little to no risk of heart disease.Out of about 1,000 people in the town, more than a dozen have lived past 100! 119 Passing on Beneficial Mutations Organisms who have a beneficial mutation will oftentimes lead longer, healthier lives. If this is the case, there is a strong possibility that these living things will give birth to many offspring who also possess this useful trait. If this is able to continue for many generations, the mutation will become more common and will be viewed as a normal variation of a trait. 120 Beneficial Mutations and Natural Selection Organisms with a beneficial genetic trait are more likely to survive to pass that trait on to their offspring. Natural selection is a gradual process wherein some traits become more or less common in a population over time. 121 Adaptation by Natural Selection Adaptation by natural selection happens over long periods of time, through many generations. Usually these changes are in response to changes in the environment. 122 Distribution of Traits As the environment changes, organisms will also change. Those traits which help them to survive better and reproduce will become more common in the population. The traits which hinder reproduction and success will become less common. Over time, the whole population will change! 123 Case Study: Peppered Moths The peppered moth is a good example of how natural selection can cause different genes to be passed on. The peppered moth varies in color from light light white/gray to black. The frequency of each color has changed drastically over the past 200 years. 124 Case Study: Peppered Moths Initially, the peppered moth population was mostly light colored. The light colored moths were camouflaged against the light colored tree trunks on which they rested. The dark colored moths were not camouflaged and they were eaten by predators. The light colored moths survived to reproduce and pass on the light colored gene to future generations. 125 Case Study: Peppered Moths With the Industrial Revolution, however, the amount of pollution dramatically increased. The air pollution caused the tree trunks to be stained a darker color. How do you think this affected the peppered moths? Write your ideas below. 126 Case Study: Peppered Moths Since the tree trunks were now a dark color, the light moths were no longer well camouflaged. They were eaten by predators while the dark moths were able to hide on the tree trunks. The dark colored moths survived to reproduce and pass on the dark colored gene to future generations. 127 Artificial Selection Humans have the ability to influence certain characteristics by selectively breeding specific traits in animals. Both of the animals to the right are dogs. How did they become so different? 128 Artificial Selection By choosing which traits are preferred in plants and animals, humans can choose to breed organisms with those specific traits. Those characteristics will then be passed on to offspring through the animal's genes. Why is this called "artificial selection"? 129 Artificial Selection There There are many ways humans can influence selection in organisms. These days, it is easy to select traits using methods such as gene therapy, artificial husbandry (breeding), and even genetic modification. 130 31 Animals reproducing on their own in the wild in response to changes to their environment is considered ___________ selection. B artificial Answer A natural 131 32 Natural selection happens very fast, often in one generation. False Answer True 132 33 Natural selection causes changes to traits in populations in response to changes in the ____________. B environment C mutations Answer A animal's DNA D father's DNA only 133 Some Mutations Are Neutral There are some mutations that have no effect, either positive or negative, on our bodies. Most mutations that occur as a result of a DNA replication error or exposure to radiation is corrected and repaired quickly by the body. Still, there are some that sneak by yet prove to not affect the organisms in a negative way. 134 Harmless Mutations Cats have a number of harmless body mutations that give variety to the species. Some cats have a mutation that causes their ears to naturally curl. Other mutations in DNA can cause cats to have a curly tail. Each of these mutations has a neutral effect on the cat. It neither helps it survive nor hurts it. 135 Harmful Genetic Mutations Harmful genetic mutations can come from an error in DNA replication in the cell, exposure to radiation, or from an error in the passing on of genetic information from parent to offspring. Just one incorrect portion of the DNA can cause a change in the entire chain. 136 34 Is the body capable of correcting mutations on its own? No Answer Yes 137 Down Syndrome One relatively common genetic disorder is Down Syndrome. A normal human baby is born with 23 pairs of chromosomes one from the mother and one from the father. What do you notice about the chromosomes to the right which came from a person with Down Syndrome? 138 Down Syndrome This genetic mutation causes significant problems for the child. Some common characteristics of individuals with Down Syndrome include: Shorter height Weaker muscles Irregularly shaped mouth, tongue, and teeth Lower IQ Heart defects 139 Genetic Disorders It is important to keep in mind that genetic disorders are never the fault of the individual who must suffer with the ailments. More often than not, a person who has a certain genetic disorder was born that way and could not help getting the disease. All living things deserve our respect! 140 Genetic Disorders Baby Project A a F1 Generation A AA Aa a Aa aa F2 Generation In this wrapup activity, you will be practicing the skills obtained during this unit and you will also be researching a genetic disorder that you will then teach to the class. 141