U1 Inheritance Teacher Notes PDF

Objectives of unit 1: inheritance, variation and evolution Part 1: Inheritance To understand, explain, draw, and label the structure of DNA To understand the relationship between genes, chromosomes, and DNA. To use the terms gene, allele, genotype, phenotype, homozygous, heterozygous, dominant, and...

Objectives of unit 1: inheritance, variation and evolution Part 1: Inheritance To understand, explain, draw, and label the structure of DNA To understand the relationship between genes, chromosomes, and DNA. To use the terms gene, allele, genotype, phenotype, homozygous, heterozygous, dominant, and recessive. To understand the use of a test cross to find the genotype of an organism showing the dominant characteristic in its phenotype To predict and explain the results of crosses involving dominant and recessive alleles, codominance, incomplete dominance, multiple alleles (examples blood groups inheritance), and sex-linked inheritance, using Punnet squares & pedigree charts. To understand and analyze test cross problems. To understand how gender is inherited in humans To interpret, evaluate and explain data and results using correct scientific reasoning. To discuss and evaluate the implications of using science and its application to solve a specific problem or issue. Activity: Who was Gregor Mendel? Biology for the IB MYP 4&5: by Concept How do characteristics pass from one generation to another? Watch this video: Gregor Mendel – YouTube and Activity: Who was Gregor Mendel? Prepare answers to the following questions for the next you may want to look at sites on the internet to lesson. You may want to look at sites on the internet, to help answer them. help you answer the following questions: 1 Who was Gregor Mendel and why is he now known 1- Who was Gregor Mendel and why is he now as the ‘father of genetics’? known as the “father of genetics” ? __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ 2- Summarize the research he carried out. How __________________________________________________________________ did this work enable him to formulate the __________________________________________________________________ concept of what we now know of as “genes”? 2 Summarize the research he carried out. How did this work enable him to formulate the concept of what we now know of as ‘genes’? __________________________________________________________________ Add your answers to the attached document and __________________________________________________________________ post it in your “Student NOTEBOOK” __________________________________________________________________ __________________________________________________________________ __________________________________________________________________  Who was Gregor Mendel? He was known as the “FATHER OF GENETICS” He discovered how traits were inherited HEREDITY – the passing of traits from parents to offspring GENETICS – study of heredity Gregor Mendel’s studies Gregor Mendel’s studies, watch this video Gregor Mendel – YouTube Video explaining Mendel’s experiment on pea plants Why did Mendel choose “Pea plants” to perform his experiments? Mendel chose to use pea plants for his experiments due to their many distinct varieties, and because offspring could be quickly and easily produced Pea plants can be self-fertilized or cross-fertilized Purebred refers to offspring resulting from a true breeding (when parents are homozygous for certain traits). True-Breeding Plants -always create plants that look like themselves (same phenotype as the parents) Hybrids – offspring of true-breeding plants HYBRIDS Mendel’s experiments steps: Mendel bred pea plants looking for many different traits like color, wrinkly or round seeds... or tall or short plants among other things. Once he had a purebred trait, he would run an experiment 1- Mendel crossed two purebred traits, green versus yellow-colored peas When the offspring grew (F1), he found that all the peas were yellow. He couldn't understand why the green trait disappeared Why didn't the peas have a 50/50 chance of being green or yellow? 2- To explore this further he took two peas from the first filial or F1 generation, that was just made, and he bred them together. When the second filial generation arrived-- F2 75% of the peas were yellow but 25% were green The green peas seemed to disappear in the F1, but reappear in the F2 generation What could be happening? Mendel decided that there were factors (which we now call genes) controlling the traits of the pea plant. The genes could be either dominant or recessive The genes could be either dominant or recessive. And dominant alleles or traits mask recessive alleles. In this case the yellow is dominant and the green is recessive. So, the purebred parents made offspring that had green and yellow alleles, but only the yellow showed because it was dominant and when the F1 generation bred, there was a chance that they could both give the recessive allele to the offspring, so the green peas showed up again. If you could look at the chromosomes in the pea plants, you would find the gene for seed color. A gene is a section of DNA that controls a trait The different seed colors have different alleles which are variations of a gene like green or yellow. You get two alleles for every gene, Because you have a set of chromosomes from mom and a set of chromosomes from dad and the same is true for plants Mendel’s experiments steps 1- Mendel crossed two purebred traits, green versus yellow- colored peas When the offspring grew (F1), he found that all the peas were yellow. 100% yellow 2- To explore this further he took two peas from the first filial or F1 generation, and he bred them together. When the second filial generation arrived-- F2 75% of the peas were yellow but 25% were green The green peas seemed to disappear in the F1, but reappear in the F2 generation Mendel decided that there were factors which we now call genes controlling the traits of the pea plant. The genes could be either dominant or recessive Mendel repeats his experiment to study the inheritance of other traits. Mendel discovered that each trait is controlled by a gene, and each gene has two alleles Gene – is a section of DNA that controls a trait Genes are located on chromosomes Alleles are variations of a gene Alleles are variations of a gene (like green peas or yellow peas are variations of the gene controlling peas’ color). You get two alleles for every gene, because you have a set of chromosomes from mom and a set of chromosomes from dad and the same is true for plants Homologous chromosomes In all living things, characteristics are passed on in the chromosomes that offspring inherit from their parents. chromosome from chromosome from female parent male parent Chromosomes are matched in pairs that contain one chromosome inherited from each parent. So, are the genes in a matching pair of chromosomes exactly the same? © Boardworks Ltd 2004 Different versions of genes The chromosomes in a matching pair contain the same type of genes that code for the same characteristics. gene for gene for petal colour petal colour version for version for red petals yellow petals Each chromosome may have a different version of a gene. Different versions of a gene, that code for different versions of a characteristic, are called alleles. Pairs of alleles – homozygous If the alleles in a matching pair are the same, they are called homozygous alleles. allele for allele for yellow petals yellow petals allele for allele for red petals red petals What colour are the flowers with these (Click twice on each bud to reveal the flower; homozygous pairs of alleles? click again to close them.) Pairs of alleles – heterozygous (Click twice on the bud If the alleles in a matching pair are different, to reveal the flower; click again to close it.) they are called heterozygous alleles. allele for allele for red petals yellow petals Which characteristic is expressed if alleles are different? Some alleles are dominant to other forms of a gene and will always be expressed. Which is the dominant allele in this heterozygous pair? Which is the recessive allele in this heterozygous pair? Representing alleles Letters are used to represent different alleles. A dominant allele is always a capital letter. allele for red petals = R A recessive allele is always the corresponding small letter. allele for yellow petals = r The allele pair for each characteristic is called the genotype. What colour are flowers with the genotype Rr? Mendel’s Principles Dominance and Recessiveness Some alleles can cover up or hide the other. The one that is expressed is DOMINANT. Genetic jargon What do these genetic terms mean? gene Section of DNA that codes for a particular trait or characteristic. allele A different form of a gene that codes for a different version of a characteristic. genotype A description of the pair of alleles present for a characteristic. phenotype The physical expression of the alleles.  Genetic jargon What do these genetic terms mean? homozygous Pair of alleles that produce a characteristic that are the same, e.g. HH. heterozygous Pair of alleles that produce a characteristic that are different, e.g. Hh. dominant An allele that will always be expressed even when there is only one of these alleles present, represented by a capital letter. recessive An allele that will only be expressed when both alleles are of this type, represented by a lower case letter. Quick Check - What do we know so far? 1. The “Father of Genetics” is ____________ 2. Genes are located on _______________ 3. The passing of traits from parents to offspring is known as _____________ 4. Genetics is the study of _____________, which is how traits are passed from _________ to ____________ 5. Mendel studied what organism? ____________ 6. Every gene is made of two: a. genotypes b. alleles c. Cells 7. The organism’s outward appearance, such as wrinkled seeds are referred to as the a) phenotype b) genotype 8. If one trait covers up another one, we say that it is ______________, the one that is covered up is _________ 9. A “true-breeding” plant is one that can only produce plants like itself a) true b) false 10. If a tall and a short plant are crossed, it will create a a) zygote b) gene c) hybrid 11. The letters (ex. RR) that represent the traits are referred to as the a) phenotype b) genotype 12. An organism that has two different alleles, or letters, such as Rr is: a) homozygous b) heterozygous 13. An organism that has two of the same alleles, or letters, such as RR is: a) homozygous b) heterozygous 14. Which of the following sets would represent Mendel’s Parent (P) generation? a)RR x RR b) Rr x Rr c) RR x rr 15. When two different alleles occur together, such as R r, the one that is expressed is a) dominant b) recessive RR x rr – crossing homozygous parents What are the possible offspring of a cross between a homozygous red flower and a homozygous yellow flower? Homozygous means that both alleles of a gene are the same. Red is the dominant allele for these flowers, so the alleles for petal colour are: red = R , yellow = r. phenotype: x genotype: RR rr  RR x rr – F1 offspring parental genotype: RR x rr gametes: R R r r r r ? F1 offspring R Rr Rr genotype: R Rr Rr What are the phenotypes of the F1 offspring?  RR x rr – F1 phenotypes parental genotype: RR x rr F1 genotypes: Rr Rr Rr Rr F1 phenotypes: (Click twice on the buds to reveal the flowers; click again to close them.) The possible offspring of a cross between two homozygous parents are always heterozygous and so the dominant characteristic is always expressed in this generation. Rr x Rr – crossing heterozygous parents The offspring (Rr) from the first cross (RR x rr) are called the F1 generation. What happens in a cross between these offspring? Both parent plants are now heterozygous, so the alleles in each plant are different. F1 generation phenotype: X genotype: Rr Rr  Rr x Rr – F2 offspring parental genotype: Rr x Rr gametes: R r R r R r ? F2 offspring R RR Rr genotype: r Rr rr What are the phenotypes of the F2 offspring?  Rr x Rr – F2 phenotypes parental genotype: Rr x Rr F2 genotypes: RR Rr Rr rr F2 phenotypes: (Click twice on the buds to reveal the flowers; click again to close them.) In the F2 generation, 3 of the 4 possible offspring are red. Only one offspring shows the recessive phenotype. When two heterozygous parents are crossed, the possible offspring will always show a 3:1 ratio in favour of the dominant phenotype. What is a test cross? A test cross allows you to find out if an organism showing a dominant characteristic is homozygous or heterozygous for the dominant allele. For example the genotype of a red flower could be: RR or Rr What could you cross a red flower with to find its genotype? Carrying out a test cross A test cross is carried out between the flower of unknown genotype and another flower whose genotype is known. For example, a yellow flower can only have the genotype rr because it’s recessive. So the test cross is: x ? rr (RR or Rr) Test cross – 2 types If the red flower is homozygous (RR) then the cross is the same as the first cross (RR x rr). All of the offspring will be heterozygous and have red petals. What about the other possible cross between a heterozygous red flower (Rr) and yellow flower (rr)? x ? rr (RR or Rr)  Test cross offspring parental genotype: Rr x rr gametes: R r r r r r ? offspring R Rr Rr genotype: r rr rr What are the phenotypes of these offspring?  Test cross results parental genotype: Rr x rr F2 genotypes: Rr Rr rr rr F2 phenotypes: (Click twice on the buds to reveal the flowers; click again to close them.) A cross between a heterozygous parent and a recessive parent yields different types of offspring in a 1:1 ratio. For your next assignment, you will be asked to complete several genetics problems on your own. Remember the steps we learned in this module. 1) Establish genotypes of parents 2) Set up the cross 3) Determine the phenotypic ratios or percentages. Tips: - Choose letters that you can easily tell capital from lowercase. - Make a little chart to show genotypes and phenotypes that you can reference. Time to work on your own! Go to Practice: Simple Genetics Problem Set Mendel’s laws: The law of segregation and The law of independent assortment Mendel cross-fertilized pea plants that had clearly opposite characteristics and, after analyzing his results, he reached two of his most important conclusions: the Law of Segregation and the Law of Independent Assortment - The law of segregation states that every individual possesses two alleles and only one allele is passed on to the offspring. - The law of independent assortment states that the inheritance of one pair of genes is independent of inheritance of another pair. PRINCIPLE OF SEGREGATION When a parent makes sperm or eggs, their genes separate. The GAMETES (egg or sperm) contain only one of the pair. PRINCIPLE OF INDEPENDENT ASSORTMENT Each trait is inherited independent of other traits. Each gamete can inherit any combination of genes Possible: GB Gb gB gb Mendel crossed plants with two separate traits to see the outcome. Consider this cross: Yellow, round seeded plant x Green, wrinkled seeded plant YYRR x yyrr What is the phenotype of the offspring? What is the genotype? What if the offspring RrYy self fertilize? YyRr x YyRr Use “FOIL” to determine the gametes created by each parent: What if the offspring RrYy self fertilize? YyRr x YyRr Set up a 4x4 Punnett Square. YR Yr yR yr Fill out the offspring by combining letters YR (keep the R’s and Y’s together) Yr Count the number for each phenotype yR Yellow, round? ______ Yellow, wrinkled? _____ yr Green, round? ____ Green, wrinkled? _____ DIHYBRID CROSSES - involve 2 traits, heterozygotes The ratio is always: 9 3 3 1 Beyond Mendel - experiments after Mendel showed there were other types of INHERITANCE PATTERNS, Non-Mendelian inheritance patterns (exceptions to complete dominance/Mendel’s studies) include: - Codominance: Both alleles are expressed in the heterozygotes - Incomplete dominance: Both alleles blend their effects - Multiple alleles. Mendel studied just two alleles of his pea genes, but real populations often have multiple alleles of a given gene. - Sex-linked alleles: Genes carried on sex chromosomes, such as the X chromosome of humans, show different inheritance patterns than genes on autosomal (non-sex) chromosomes. Codominance → both alleles are expressed in the heterozygotes, alleles do not blend An example of codominance is the roan cow which has both red hairs and white hairs. RR = Red Cow RW = Roan Cow (heterozygote) WW = White cow Show the cross of a red cow and a roan cow:  Some genes did seem to “blend” together... In incomplete dominance a heterozygous individual blends the two traits. An example of incomplete dominance is the pink snapdragon, which receives a red allele and white allele. A white flower is crossed with a red flower. All of the offspring are pink. RR = red Rr = pink rr = white This is called: INCOMPLETE DOMINANCE Both alleles blend their effects Application In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (r). The heterozygous genotype is expressed as pink. a. What is the phenotype of a plant with the genotype RR? ___________ b. What is the phenotype of a plant with the genotype Rr? ___________ c. What is the phenotype of a plant with the genotype rr? ___________ A pink-flowered plant is crossed with a white-flowered plant. What is the probability of producing a pink-flowered plant? ___________% What cross will produce the most pink-flowered plants? Show a Punnett square to support your answer and explain. Multiple allele traits Traits controlled by a single gene with more than two alleles are called multiple allele traits. The majority of human genes are thought to have more than two normal versions or alleles. Traits controlled by a single gene with more than two alleles are called multiple allele traits. An example is ABO blood type. There are three common alleles for this trait, which are represented by the letters IA, IB, and i. Multiple Allele Traits - more than two alleles control the trait. Ex: Blood Type Blood Type/ Phenotype Genotype A IAIA and IAi (AA, AO ) B IBIB and IBi (BB, BO) AB IAIB (AB) (codominant) O ii (OO) (recessive) As shown in the table above, there are six possible ABO genotypes because the three alleles, taken two at a time, result in six possible combinations. The IA and IB alleles are dominant to the i allele. As a result, both IAIA and IAi genotypes have the same phenotype (type A blood). Similarly, both IBIB and IBi genotypes have the same phenotype (type B blood). People with the ii genotype have phenotype (type O blood). For the genotype IAIB ,alleles IA and IB are codominant to each other. IAIB heterozygotes have a unique phenotype (type AB blood). Application Show the cross between the blood types below: AB x O AO x BO O x O What are the genotypes and the phenotypes of the offspring for each cross?  Donor/Recipient Your blood type refers to which of certain proteins called antigens are found on your red blood cells. For example: -People with blood type A, have antigen A on their red blood cells and antibody: Anti-B in their plasma. So, people with type A blood can donate blood to individuals who have blood type A or type AB, and they can receive blood from individuals with type A or type O. -If a person type A receives blood from the other types (type B or type AB), a severe life-threatening reaction can occur (Blood agglutination). This is because antigens and antibodies stick together, which then makes the blood cells stick together/agglutinate. Thus, a person with type A blood cannot be given blood from somebody with type B because the anti-B antibodies would stick to the antigen B on the blood cells from the donor. Blood Agglutination For a blood transfusion to be successful, ABO and Rh blood groups must be compatible between the donor blood and the receiver/patient blood. If they are not, the red blood cells from the donated blood will clump or agglutinate. The agglutinated red cells can clog blood vessels and stop the circulation of the blood to various parts of the body. The agglutinated red blood cells also crack and its contents leak out in the body. The red blood cells contain hemoglobin which becomes toxic when outside the cell. This can have fatal consequences for the receiver/patient. The A antigen and the A antibodies can bind to each other in the same way that the B antigens can bind to the B antibodies. This is what would happen if, for instance, a B blood person receives blood from an A blood person. The red blood cells will be linked together, like bunches of grapes, by the antibodies. As mentioned earlier, this clumping could lead to death. Application: Blood Agglutination If a patient with type B blood received a transfusion of type AB blood, predict and explain what would happen? Blood agglutination would occur, blood will clump, because type AB blood has A antigens on the surface of red blood cells (along with B antigens), Also someone with type B blood will have anti-A antibodies in their blood. So, antigen A and anti-A antibodies will combine/stick together and cause blood agglutination and clog blood vessels and stop the circulation of the blood to various parts of the body. Answer the question below: Is it possible for a couple to have four children, each child showing a different blood type? Explain your answer POLYGENIC TRAITS - When many genes control one trait, usually resulting a wide RANGE of phenotypes Polygenic traits are traits that are controlled by multiple genes instead of just one. The genes that control them may be located near each other or even on separate chromosomes. Because multiple genes are involved, polygenic traits do not follow Mendel’s pattern of inheritance. Instead of being measured discretely, they are often represented as a range of continuous variation (a bell-shaped spectrum of potential phenotypes) Some examples of polygenic traits in human are: height, skin color, eye color, and hair color. Polygenic traits may also be influenced by environmental factors One example of a polygenic trait that is influenced by environmental factors is human height Human height is controlled by multiple genes (polygenic), resulting in a bell- shaped spectrum of potential phenotypes Environmental factors such as diet and health (disease) can further influence an individual human’s height Another example of a polygenic trait that is influenced by environmental factors is human skin color Skin color is controlled by multiple melanin producing genes, but is also affected by factors such as sun exposure Choose the correct answer