Mendelian Genetics Presentation PDF

UNIT 3 Chapter 17: Mendelian Genetics  TOPIC 1: MONOHYBRID CROSSES ○ Genes vs. alleles ○ Genotype vs. phenotype ○ Autosomal dominant vs. autosomal recessive modes of inheritance ○ Mendel's Law of Segregation ○ Monohybrid Crosses & Punnett squares ○ Test crosses...

UNIT 3 Chapter 17: Mendelian Genetics  TOPIC 1: MONOHYBRID CROSSES ○ Genes vs. alleles ○ Genotype vs. phenotype ○ Autosomal dominant vs. autosomal recessive modes of inheritance ○ Mendel's Law of Segregation ○ Monohybrid Crosses & Punnett squares ○ Test crosses Textbook pgs. 596-603  Selective Breeding We’ve been doing it for longer than most people realize… o “Accidental” selective breeding of wheat began as early as 9000 BC in the Middle East o Farmers were able to collect and plant the seeds of one variety of wheat more easily than the other, thus “selecting for” this former strain without realizing it Through an understanding of genetics, we have been able to take advantage of selective breeding, leading to the development of new varieties of organisms with desirable traits and behaviours Other species that are the product of selective breeding: But how does it work??? ? ? ○ Gene: Section of DNA, personalized instructions to specify physical and biological traits ○ Allele: Alternative forms of genes. (One letter) Alleles: alternative versions of a gene ○ Genotype: Refers to the alleles an individual receives at fertilization. ○ Allele combination(Two letters) ○ One from the mother and one from the father ○ Capital letters always are first. ○ Phenotype: Physical appearance based on genotype. ○ What we see ○ Protein produced from alleles. Example: This child’s dad donated an allele encoding brown eyes. Her mom donated an allele encoding blue eyes. Because the “brown eye” allele or “B” is dominant to the “blue eye” allele or “b”, her eyes appear brown rather than blue. ○ Dominant Allele: DNA that produces fully functioning protein. ○ Capital Letter “B” ○ Recessive Allele: DNA that produces a protein with little or no function. ○ Lower case Letter “b” ○ Homozygous: Genotype with the same alleles. ○ Heterozygous: Genotype with different alleles. Oh come on! That’s “allele” funny… B x B = BB (homozygous dominant) o Both parents give a dominant allele o Results in dominant phenotype B x b = Bb (heterozygous) o One parent gives a dominant allele, the other parent gives a recessive allele o Results in dominant phenotype b x b = bb (homozygous recessive) o Both parents give a recessive allele o Results in recessive phenotype People Thought Blending Concept of Inheritance ○ 19th century scientists thought blending of offspring lead to organisms genetics. ○ Some evidence did support concept, red and white flowers producing pink flowers. ○ However some evidence disproved hypothesis, two pink flowers producing red and white flowers. What Actually happened (no blending) Gregor Mendel ○ Austrian Monk ○ Experiments took place in 1850s – 1860s ○ Studied math and botany and University of Vienna. ○ Educated ○ Substitute natural science teacher at a local high school. ○ Experiments took place in the 1860s. ○ One of the first scientists to apply math to biology. ○ Also followed the scientific method very closely.  Mendelian Genetics The idea of dominant and recessive alleles was first described by Gregor Mendel… o He conducted test crosses with peas of different phenotypes and realized that for each trait, offspring displayed either the maternal or paternal phenotype rather than a blending of the two. o E.g. a true-breeding plant with purple flowers crossed with a true-breeding plant with white flowers always produced offspring with purple flowers, not light purple as previously suggested by the blending theory of inheritance o Thus, he concluded that purple flowers were dominant to white Link Principles of Heredity Mendel’s experiments allowed him to develop three fundamental principles of heredity: Law of Dominance Law of Segregation Law of Independent Assortment These will be discussed in more depth as we go through his experiments LAW OF DOMINANCE ○ Only one form of the trait will appear in the next generation. ○ If organism inherits at least one dominant allele, they will exhibit the dominant phenotype. ○ If organism inherits two recessive alleles, they will exhibit recessive phenotype. Law of Segregation ○ Each organism has two factors for each trait. ○ Factors separate during meiosis. ○ Each gamete contains only one of the factors. ○ The observation that offspring display either the maternal (female) or paternal (male) phenotype ○ Eggs and Sperm fuse randomly and the embryo that develops now has two copies of each factor but only shows one Law of Segregation VIDEO: watch for extra review Law of Independent Assortment Alleles for a trait separate when gametes are formed. ○ These allele pairs are then randomly united at fertilization VIDEO: watch for extra review Some traits studied by Mendel: Each trait is controlled by a single gene or set of alleles  Generations P generation: true- breeding parental generation F1 generation: (first filial) hybrid offspring of P generation F2 generation: (second filial) offspring of the F1 generation Punnett Square ○ British Scientist ○ Created by Reginald Punnett ○ Wrote book called “Mendelism” ○ Created first Journal on Genetics ○ What we use to predict generations Monohybrid Crosses https://www.youtube.com/watch?v=i-0rSv6oxSY  So, as long as we know the genotype of individuals being crossed, we can determine the ratio and potential genotypes of their offspring.  Because of the particular way in which chromosomes align during metaphase I of meiosis, each of the four allele combinations is as likely as the other. Mendel’s test crosses yielded some very interesting patterns… Predict the F1 Generation of crossing RR x rr Predict the F2 Generation of crossing Rrx Rr  MENDEL’S TEST CROSSES: o Because all of the offspring from the initial cross (F1 gen.) are round, we know that round is dominant to wrinkled. o Parents are “purebred”; thus, the genotype of round parental plants is RR, and that of wrinkled parental plants is rr RR x rr can be represented as:  MENDEL’S TEST CROSSES CONT’D Parents are RR (round) and rr (wrinkled), and F1 offspring are all Rr (round): Now that we know the genotype of F1 individuals, we can use the same process to determine the genotype of F2 individuals…  MENDEL’S TEST CROSSES CONT’D Recall that the F2 generation are the offspring of a cross between individuals of the F1 generation: MENDEL’S TEST CROSSES CONT’D Rr x Rr can be represented as: Remember The Law of Segregation: All individuals have two copies of each gene. These copies segregate randomly during gamete formation, and each gamete receives one copy of every gene. How to Solve Genetics Problems 1. Write down the symbols for the alleles (sometimes they are given to you) 2. Write down the genotypes given If phenotypes are given, then write down the possible genotypes 3. Determine what the problem is asking, and write out the cross as: [genotype] x [genotype] 4. Set up the Punnett square  Practice Problems In cats, short hair is dominant to long hair. A true- breeding short haired cat is crossed with a cat that is heterozygous for the trait. What percentage of the offspring will have long hair? H = short hair h = long hair H h H HH Hh Answer: 0% of the offspring will have long H HH Hh hair  Practice Problems Purple (P) is dominant to white (p) flowers. In a homozygous dominant purple plant, what gametes would be produced? What about in a plant that is heterozygous? Answer: the homozygous dominant plants gametes would all be P. The heterozygous plants gametes would be P or p.  Monohybrid Crosses (Where only a single trait is considered) Example: In mice, black fur is inherited in an autosomal dominant manner (black fur is dominant to brown fur)... a) List the genotypes of a black mouse and a brown mouse. b) If a heterozygous black mouse is crossed with a brown mouse, what is the probability that their offspring will have black fur? Brown fur? ? c) If two heterozygous black mice are crossed, what will be the genotypic and phenotypic ratio of their offspring? ? d) Is it possible for a homozygous black mouse and a heterozygous black mouse to have “grandchildren” that are brown?  Test Crosses An individual with the dominant phenotype could be either homozygous (BB) or heterozygous (Bb). By performing a test cross, we can determine the true genotype of such individuals. Cross the unknown individual with an individual who displays the recessive phenotype (because their genotype is known): If homozygous, all If heterozygous, ½ of offspring will show offspring will show dominant phenotype recessive phenotype  Let’s Try Practice Questions  TOPIC 2: DIHYBRID CROSSES ○ Dihybrid crosses ○ Independent assortment Textbook pgs. 596-603  TOPIC 2: DIHYBRID CROSSES I CAN... Describe the evidence for dominance, segregation & the independent assortment of genes on different chromosomes, as investigated by Mendel [C2.1k] Interpret patterns & trends of inheritance of traits & predict, quantitatively, the probability of inheritance of traits illustrated in...dihybrid inheritance, using… Punnett squares [part of C2.3s]. Dihybrid and Two-Trait Crosses https://www.youtube.com/watch?v=qIGXTJLrLf8 Dihybrid AaBb Gamete #1 Gamete #2 Gamete #3 Gamete #4 AB Ab aB ab Dihybrid Cross: Cross between two different traits.  Dihybrid Crosses Mendel also conducted experiments to determine whether the pattern of segregation of alleles for one gene had any influence on that of another gene… E.g. Plant size and pod colour: Are plants with the “tall” allele just as likely to have the allele that encodes green pods as the allele that encodes yellow pods? Two true-breeding plants for two different traits are crossed… ttgg F1 Generation: Like in the F2 generation of Mendel’s monohybrid crosses, crossing of F1 individuals produces a predictable phenotypic ratio in the F2 generation of dihybrid crosses as well…  TtGg x TtGg Possible Gametes: F2 Generation:  Because such crosses consistently yielded this 9:3:3:1 ratio, Mendel concluded that the segregation of alleles for one gene had no influence on the segregation of alleles for another gene… This is known as Mendel’s Law of Independent Assortment: The two alleles for one gene segregate independently of alleles for other genes during gamete formation. All the different Combinations that could occur (independently) For Extra explanation A beginner’s guide to Punnett Squares https://www.youtube.com/watch?v=Y1PCwxUDTl8&t=6s  Practice Problems In pea plants, purple flower color is dominant to white flower color, and round pods are dominant to wrinkled pods. If a true breeding purple flowered round pod plant is crossed with a true breeding white flowered wrinkled pod plant, what will the resulting F1 generation be? Hint: don’t do a punnett square Cross: PPRR x pprr P = purple p = white R = round Gametes: PR pr r = wrinkled All offspring: PpRr  Practice Problems In pea plants, purple flower color is dominant to white flower color, and round pods are dominant to wrinkled pods. If a plant that is heterozygous for both traits is self crossed, what will the phenotypic ratios of the F1 generation be? P = purple p = white Cross: PpRr x PpRr R = round How do you find the gametes? FOIL r = wrinkled PpRr x PpRr PR Pr pR pr x PR Pr pR pr  Practice Problems Now set up the Punnett square with the gametes and perform the cross Cross: PpRr x PpRr P = purple p = white PR Pr pR pr R = round r = wrinkled PR Pr pR pr  Practice Problems Go through and determine the phenotypes Cross: PpRr x PpRr P = purple p = white PR Pr pR pr R = round r = wrinkled PR PPRR PPRr PpRR PpRr Purple/round: 9/16 Pr PPRr PPrr PpRr Pprr Purple/wrinkled: 3/16 pR PpRR PpRr ppRR ppRr White/round: 3/16 pr PpRr Pprr ppRr pprr White/wrinkled: 1/16 Phenotypic ratio 9:3:3:1 DIHYBRID CROSSES Example 1: In tomatoes, red fruit is dominant to yellow fruit, and tall plants are dominant to short plants. A plant that is heterozygous for both traits is crossed with a plant that is heterozygous for the gene encoding height, and homozygous recessive for the gene encoding fruit colour. a) What are the phenotypes & genotypes of the plants being crossed? b) What proportion of offspring will be… ○ tall with red fruit? ○ tall with yellow fruit? ○ short with red fruit? ○ short with yellow fruit?  TOPIC 3: OTHER MODES OF INHERITANCE ○ Incomplete dominance ○ Co-dominance ○ Sex-linked traits ○ Multiple alleles ○ Blood types Textbook pgs. 596-603  TOPIC 3: OTHER MODES OF INHERITANCE I CAN... Compare ratios & probabilities of genotypes & phenotypes for dominant & recessive, multiple, incompletely dominant & codominant alleles [C2.2k] Interpret patterns & trends of inheritance of traits & predict, quantitatively, the probability of inheritance of traits illustrated in sex- linked inheritance using Punnett squares… [part of C2.3s] Genetic Recombination ○ Boveri-Sutton Chromosomal Theory of Inheritance: ○ Chromosomes are inherited from parents. ○ Chromosomes code for traits of offspring. ○ 1902 and 1903 Thomas Hunt Morgan ○ Studied fruit flies even more. ○ Analyzed certain gene frequencies. ○ Ratios didn’t make sense. ○ Looked at eye color, wing shape, leg length Alfred Sturtevant ○ Student of Morgan ○ One night, blew off homework. ○ Figured out crossing over. (see later in notes) ○ That is why the ratio of offspring didn’t match with predictions  Other Modes of Inheritance INCOMPLETE DOMINANCE o Occurs when neither allele on a particular gene can conceal the presence of the other (i.e. there is no true “dominant” allele) o Two alleles of the same variety are required to fully express their phenotype; heterozygotes thus display partial expression of each o Upper and lowercase letters not used when representing incomplete dominance Example: In some varieties of flowering plants, petal colour is determined by two alleles which demonstrate incomplete dominance. One version of the allele, R1, encodes red flowers, while another version of the allele, R2, encodes white flowers. a. Determine the genotype of each of the following plants: A plant with red flowers A plant with white flowers A plant with pink flowers a. A plant with red flowers is crossed with a plant with pink flowers. What proportion of offspring will also have pink flowers? b. Is it possible for the cross described in part b to produce offspring with white flowers? Explain.  Another example: Sickle-cell anemia is one form of incomplete dominance where heterozygotes actually have increased fitness under certain circumstances… Sickle-cell anemia (incomplete dominance): If a homozygous man with normal blood cells has children with a heterozygous woman, what is the probability that their children will be born with severe anemia? What proportion of their children will be more likely to survive if exposed to malaria?  CO-DOMINANCE o Both alleles on a particular gene are fully expressed (i.e. two equally “dominant” alleles) o Both alleles require just one copy to fully express their phenotype; heterozygotes thus express one allele in certain cells and the opposing allele in others ○ Codominance: Several alleles are dominant. ○ Both phenotypes are expressed. ○ Roane Cows have two alleles that are dominant to each other. ○ R: Red ○ W: White RRxWW RWxRW Example: In other varieties of flowering plants, petal colour is determined by two alleles which demonstrate co- dominance. One version of the allele, R1, encodes red flowers, while another version of the allele, R2, encodes white flowers. a. Determine the phenotype of each of the following plants: R1R1 R2R2 R1R2 a. A plant with red flowers is crossed with a heterozygous plant. What proportion of offspring will also have red flowers? b. Is it possible for the cross described in part b to produce offspring with white flowers? Explain. ○Sex-linked Gene: Any gene that is located on a sex chromosome. ○In humans, most sex-linked genes are found on the X- Chromosome.  SEX-LINKED TRAITS o Genes that are located on the X or Y chromosome display different inheritance patterns than genes located on autosomes o This is because males do not receive an X- chromosome from their father, and females must Colour blindness is a inherit their father’s recessive trait carried on single X-chromosome the x-chromosome ○ Sex-Linked Disorders ○ Males only need 1 copy of a sex-linked disorder on a X-chromosome to produce the phenotype. ○ XhY ○ Females need two X-chromosomes with disorder. ○ XhXh ○ Carrier: Individual who has one copy, but doesn’t have the disorder.  Sex-Linked Inheritance ○ Traits controlled by genes on either the X or the Y chromosome ○ Y-linked ○ Males to their son ○ Females not carrier ○ Why: females have no Y chromosome ○ Example: hairy ears ○ X-linked ○ Fathers can pass X-linked to ALL daughters but NO sons ○ Mothers can pass X-linked to both daughters and sons ○ Y-Linked Disorders ○ Always passed from father to son. ○ Males only have this disease. ○ Rare ○ Less genes on Y chromosome. ○ 100% chance guys will inherit disease. ○ Example: Hair Ears Inheritance of X-Linked Genes N = normal Affected father Affected mother n = affected XNXN x XnY XNXn x XNY Xn Y XN Y Complete the Punnett Squares to determine the XN X X N n X Y N XN XNXN XNY outcome of the affected parents. XN XNXn XNY Xn XNXn XnY If an X-linked trait is due to a RECESSIVE allele: Females will only express trait if they are homozygous recessive Because males only have one X chromosome, they will express the trait if they inherit it from their mother  They are called hemizygous (since the term heterozygous does not apply)  Due to this males are much more likely to have an X- linked disorder X-Linked Disorders 1. Duchenne muscular dystrophy Progressive weakening of muscles 2. Hemophilia Inability to properly clot blood 3. Color blindness Inability to correctly see colors  Example: Colour Blindness (Mode of inheritance: X-linked recessive, males can only receive disorder from the mother) o In females, two recessive alleles are required to express the colour blind phenotype. o In males, there is no second X-chromosome to carry another allele; thus, only one recessive allele is required to express the colour blind phenotype. This is why colour blindness is more common in males.  Example: A colour blind man and a woman homozygous for normal vision have three children: two girls and a boy. a) What is the probability that their son is colour blind? b) What is the probability that their daughters will both be carriers for the allele that encodes colour blindness? c) What is the probability that they will have colour blind grandchildren?  What scenario would have to exist for a colour-blind man and normal woman to produce colour-blind daughters?  BARR BODIES Although females carry two X-chromosomes in each of their cells, only one of these chromosomes is active; the other one condensed into what is called a Barr Body. The particular X-chromosome that is inactivated in each cell is completely random. This mode of inheritance accounts for the colour patterns seen in calico cats (female only!)  MULTIPLE ALLELES Often, more than two alleles may exist for a particular trait (i.e. although an organism only inherits two alleles for each gene, many different alleles can exist within the population) In humans, for example, a single gene determines blood type. However, three different alleles exist: IA, IB, and i Note: the gene is designated “I” or “i” depending on the presence of an antigen. IA thus indicates the presence of an A antigen on red blood cells, and IB indicates the presence of a B antigen. The absence of an antigen is marked by “i”  Alleles for blood type: IA, IB, and i Different combinations of these three alleles produce four different phenotypes, which are commonly referred to as A, B, AB, or O. A = IAIA or IAi B = IBIB or IBi AB = IAIB O = ii Alleles IA and IB are equally dominant to one another, but both are dominant over allele i (order of dominance): IA = I B > i Multiple Alleles EXAMPLE: A woman homozygous for blood type A has a child with a man heterozygous for blood type B. What is the probability that their child has the blood type AB? ½ of offspring will have the AB blood type  Blood Typing Problem ○ A man with type AB blood marries a woman with type O blood. ○ Give the genotypes and phenotypes of all possible offspring.  Multiple Alleles Three or more alternative forms of a gene (alleles) that can occupy the same locus, only two of the alleles can be present in a single organism Example: the ABO system of blood groups is controlled by three alleles, only two of which are present in an individual. Refer to Page 606 1. Read thru the Sample Problem 2. Complete Practice Problems 11, 13, 15, and 17 Blood Antibodies Reaction When Blood from Groups Below Is Mixed Group Present in with Antibodies from Groups at Left (Phenotype) Genotypes Red Blood Cells Blood O A B AB O ii Anti-A Anti-B IAIA A or Carbohydrate A Anti-B IAi IBIB B or Carbohydrate B Anti-A IBi AB IAIB — A single gene determines a person's ABO blood type and the type of antigen (if any), that is attached to the cell membrane Watch the Video for extra review……  POLYGENIC INHERITANCE Many traits are controlled by more than one gene. As a result, phenotypes vary gradually from one extreme to another rather than displaying two discrete forms. These are referred to as continuous traits… Skin colour and height are two examples of polygenic inheritance.  PLEIOTROPIC GENES Often, a single gene is responsible for influencing more than one trait. These genes are said to be pleiotropic. An example of pleiotropy is phenylketonuria (PKU), an inherited disorder that affects the level of phenylalanine in the body. Phenylalanine, an amino acid, is encoded by a single gene on chromosome 12. Mutation of this gene cause phenylalanine levels to increase in the body, affecting multiple body systems. Symptoms of PKU include seizures/tremors, stunted growth, skin conditions, and a musty odour on the breath. Pleiotropy explains why a mutation to a single gene can have such a wide array of consequences. ○ Albinism: Skin, hair, other physical features are affect by one mutation. ○ ○ Dwarfism: Lack of growth hormone leads to abnormally short height. ○ Achondroplasia  TOPIC 4: GENE LINKAGE & MAPPING ○ Evidence for gene linkage ○ Parental vs. recombinant gametes ○ Gene mapping Textbook pgs. 596-603 Genes and the Environment The expression of genes in an organism can be influenced by the environment, including the external world in which the organism is located or develops, as well as the organism's internal world, which includes such factors as its hormones and metabolism. Gene Recombination Overview https://www.youtube.com/watch?v=TU44tR0hJ8A  GENE LINKAGE Typically, the inheritance of a particular trait is thought to follow Mendel’s law of independent assortment, allowing us to accurately predict the phenotypic and genotypic ratios of offspring. Occasionally, however, genes may be observed as “breaking” this rule… o E.g. people with blue eyes are more likely to have blonde hair, and people with brown eyes are more likely to have brown hair. o This is because the genes for hair & eye colour are found close together on the same chromosome; they are said to be linked. Linked Genes: Crossing Over Linked genes show parental phenotypes in offspring at higher than 50% During crossing over chromosomes from one paternal chromatid and one maternal chromatid exchange corresponding The further apart two genes are on the same chromosome the higher the probability that a crossing over event will occur between them and the higher the recombination frequency Genetic Recombination Production of offspring with a new combination of genes from parents Parental types: offspring with the parental phenotype Recombinants: offspring with phenotypes that are different from the parents Genetic Recombination ○Linked Genes: Genes located on the same chromosome. ○ The closer two genes are together, the more likely they will be inherited together. ○ Recombinant DNA: Genes where crossing over has occurred between them. ○ Unlinked Genes: Genes are different chromosomes. ○ The further two genes are apart, the more likely that will be recombined.  Example: Hair & Eye Colour In humans, the genes that encode hair and eye colour are found on the same chromosome… o The allele for brown eyes (B) is dominant to the allele for blue eyes (b). o The allele for brown hair (H) is dominant to the allele for blonde hair (h). o The individual whose chromosome is pictured above thus has the genotype BbHh (has brown eyes and brown hair) When this individual produces gametes, we would expect to see equal proportions of gametes with the following genotypes (Independent Assortment): Half of these gametes are the parental type (from the same chromatid), and half are recombinants (produced by crossing over and exchange of DNA between chromatids) No linkage: Your results from the cross has the ratio you predict Genes are linked….ratio not what you expected However, because the genes for hair and eye colour are on the same chromosome, they will undergo crossing over less often, causing them to produce fewer recombinant gametes… Non-linked genes = 50% parental gametes, 50% recombinants Linked genes = less than 50% recombinants c  In Summary... o Genes are more likely to be linked if they are found on the same chromosome o We know that two genes are linked if we see gametes with more parental genotypes than recombinant genotypes (because crossing over occurs less frequently when genes are on the same chromosome) o We also know that two genes are linked if we see a different ratio of parental & recombinant offspring than predicted  Gene Mapping The relative distance between two genes on the same chromosome may be determined using a method known as gene mapping. Recall that in non-linked (“normal”) genes, 50% of gametes will be parental, and 50% will be recombinant. In linked genes, less than 50% of gametes will be recombinant due to reduced frequency of crossing over. Genes that are closer together cross over less frequently. So, the lower the recombination frequency, the closer together they are. For example, genes H and d will cross over less than genes B and H, producing fewer recombinant gametes.  Ascending order: Practice Questions list linkage least to highest linkage strength ABCD  * Note that a recombination frequency greater than 50% indicates that the genes may be on different chromosomes (or are very far apart on the same chromosome)  TOPIC 4: PEDIGREES ○ Pedigree symbols ○ Use of pedigrees to determine genotype ○ Use of pedigrees to determine mode of inheritance Textbook pgs. 596-603 Pedigrees  Pedigrees A pedigree is a type of flowchart that uses symbols to show the expression of a particular trait through multiple generations of a single family. ○ Lines between individuals represents the couple having an offspring. ○ Circles and Squares below are offspring.  PEDIGREES Roman numerals are used to indicate generations. Numbers are used to indicate individuals within each generation. 0 PRACTICE: 1. How many offspring are produced by the individuals shown in generation 1? 2. Is individual 3 of generation II male or female? 3. List the offspring produced by individuals 2 & 3 of generation II. 4. How many individuals in total comprise generation IV? First generation (grandparents) Ff Ff ff Ff Second generation (parents, aunts, and uncles) FF ff ff Ff Ff ff or Ff Third generation (two sisters) ff FF or Female Male Ff Affected Unaffected ○ Autosomal Recessive ○ Use letters ○ Skips generations ○ Affected: aa ○ Not affected: At least one A ○ Carrier: Don’t express the trait, but still have one allele. ○ Half shaded in.  PEDIGREES Predicting mode of inheritance Example = Autosomal Recessive Albinism: An Example ○ Expressed in both sexes at approximately equal frequency. ○ Thus, autosomal. ○ Not expressed in every generation. ○ Thus, recessive. Albinism: Genotype the Affected Individuals ○ Assign codes for the alleles. ○ Code “A” for the dominant normal allele. ○ Code “a” for the recessive allele for albinism. ○ Affected individuals must be homozygous for “a.” ○ First generation parents must be “Aa” because they have normal phenotypes, but affected offspring. Albinism: Genotype the Normal Individuals ○ Normal individuals must have at least one “A.” Albinism: Parent-Offspring Relationships ○ #1 must transmit “a” to each offspring. ○ The “A” in the offspring must come from the father. ○ Normal father could be either heterozygous or homozygous for an “A.” ** Albinism: Parental Genotypes are Known ○ Both parents are heterozygous. ○ Normal offspring could have received an “A” from either parent, or from both. Albinism: One Parental Genotype is Known ○ Only the genotype of the offspring expressing albinism are known. ○ Normal offspring must have received an “a” from their affected father. Autosomal Dominant ○ Use letters ○ Doesn’t skip generations ○ Affected: At least one A ○ Not affected: aa ○ No carriers  PEDIGREES Predicting mode of inheritance Example #1 = Autosomal Dominant Marfan’s Syndrome: An Example ○ Expressed in both sexes. ○ Thus, autosomal. ○ Expressed in every generation. ○ Thus, dominant. Marfan’s: Genotype the Normal Individuals ○ Assign codes for the alleles. ○ Code “m” for the recessive normal allele. ○ Code “M” for the dominant allele for Marfan’s syndrome. ○ Normal individuals must be “mm.” Marfan’s: Genotype the Affected Individuals ○ Affected individuals must have at least one “M.” Marfan’s: Parent-Offspring Relationships ○ Possibilities for #1 and #2: Heterozygote (Mm) or homozygous for “M?” ○ If “MM,” all offspring from a normal mate should be affected. ○ Therefore, both must be heterozygotes. Marfan’s: Parental Genotypes Known ○ “M” must have come from the mother. ○ The father can contribute only “m.” ○ Thus, the remaining genotypes are “Mm.” X-Linked Recessive Affected Females: XhXh ○ Affected Males: XhY ○ Unaffected Females: XHXH , XHXh ○ Unaffected Males: XHY X-linked Dominant ○ Affected Females: XHXH, XHXh ○ Affected Males: XHY ○ Unaffected Females: XhXh ○ Unaffected Males: XhY Hairy Ears: An Example ○ Only males are affected. ○ All sons of an affected father have hairy ears. ○ Thus, hairy ears is Y-linked. Hairy Ears: Female Sex Determination ○ All females are XX. Hairy Ears: Male Sex Determination ○ All males are XY. Hairy Ears: Gene on the Y Chromosome ○ Code “H” indicates the allele on the Y chromosome for hairy ears. RE-CAP: PEDIGREE ANALYSIS Page 615 ○ 18-21