Genetics A. Heredity B. Homozygous C. Heterozygous D. Trait E. Monohybrid Cross F. Hybrid G. Dihybrid Cross H. Gene I. Segregation J. Alleles K. Independent Assortment L. Dominant M. Incomplete Dominance N. Recessive O. Codominance P. Phenotype Q. Multiple Alleles R. Genotype S. Polygenic Traits T. Genetics Blending It was believed that if parents had different traits, and reproduced to have offspring, the traits of the offspring would be a blend of the two parents. Tall (female) X Short (Male) Would produce medium offspring Dark Hair X Blonde hair Would result in? Segregation Genetics Genes and Dominance Mendel's F 2 F 1 Generation P Generation F 2 Generation Heredity: : is the set of characteristics an organism receives from its parents (gametes) We aren t the only organisms with parents: trees, fish, dogs, jellyfish, etc. Mendel s F 1 Crosses on Pea Plants Tall Short Tall Tall Tall Tall Tall Short Gregor Mendel (1800 s): first person to study genetics, he used true- breeding pea plants, his work disproved the blending hypothesis. Traits: characteristics which distinguish one individual from another He studied seven traits in particular (see page 126) Seed shape Seed color Seed coat color Pod shape Pod color Flower position Plant Height Genes and Dominance Mendel s Seven F 1 Crosses on Pea Plants Mendel s F 1 Crosses on Pea Plants Gregor Mendel s s Peas Mendel knew that the male part of each flower produces pollen, (containing sperm). the female part of the flower produces egg cells. Mendelian Genetics: Mendel s s Work he used pea plants which had noticeable/different traits and were true-breeding he stopped self-pollination by removing the male parts of the plants. He cross-pollinated plants with different traits. 1
Gregor Mendel s s Peas This process is called cross- pollination. Mendel was able to produce seeds that had two different parents. More Terms Related to Mendel s s Work Mendel s work: page 126 P generation: parents with different traits F1 generation: hybrids, offspring of parents with different characteristics F2 generation: offspring resulting from an F1 cross Plant Reproduction Plant reproduction:(p.125) plants use flowers to reproduce flower parts: one part produces pollen (male gametes) one part produces eggs (female gametes) Pollination: when pollen and eggs combine to form a seed. 1. Self-pollination: Plants have both male and female parts - (one parent) 2. Cross Pollination: pollen from one plant and an egg from another combine to make a seed - (two parents) Pea Plants can self-pollinate, why would this have been a problem for Mendel? Class survey of some traits: Dimples Double-jointed thumbs Ear lobes Eye color Hand folding Freckles Sex male or female Hair color Middigital hair Because traits didn t blend, Mendel concluded that some unit determined traits. Genes: : are the units of DNA that determine traits. What is the connection back to protein synthesis? Are everyone s genes the same? Does every trait have only one type of expression (Hint: does everyone have brown eyes)? Do finger print activity Low, Least Medium, Most High Make a karyotype Karyotype Karyotype on computer Other activities Have students use the laptops and create a karyotype for a normal male or female. Go to other activities and discuss turners, klinefelter,, Down syndrome and cri du chat What is a gene? Sequence of DNA that codes for a particular protein. AATTTCCTGGAATTCCTTA This section of DNA codes for the production of protein therefore it is a gene. That protein contributes to a specific trait. GENES COME IN DIFFERENT VERSIONS: Example one gene may say tall pea plants and another may say short. WE USE LETTERS TO REPRESENT THE ALLELES 2
Alleles: contrasting versions of a gene. Simply put, alleles are variations in nucleotide sequences. Expression of Alleles Heterozygous: Mixed pair of alleles for a trait. Example: Tt, Yy, Homozygous: Identical pair of alleles for a trait. Example: TT, YY, tt Dominant allele: Requires only one allele to be expressed It is represented by a capital letter Recessive allele: Requires both alleles in order to be expressed It is represented by a lower case letter Genotype versus Phenotype Genetic Crosses Make babies Genotype: the genetic makeup of an organism The letters Ex. Bb, DD, hh, etc. Phenotype: the expression of the genetic makeup of an organism Traits what an organism looks like Does include nonvisible traits Monohybrid: Tt X TT YY X yy Aa X aa Dihybrid TtYy X TtYy Dominance Because an allele for a particular characteristic is dominant does not necessarily mean that it is more common in a population. 1 baby out of 400 in the united states is born with extra fingers and toes, a condition known as polydactyly. The allele for polydactyly is dominant over the 5 fingered allele. A father is polydactyl and the mother has the normal phenotype, they have had one normal child. What is the genotype of the mother? What is the genotype of the father? What is the probability that a second child will have the normal number of digits? Skipping a generation Mendel s s Principles 1. Individual units called genes determine biological characteristics. 2. For each gene an individual receives an allele from each parent. (segregation) 3. One allele may be dominant over the other. 4. Independent assortment: genes that segregate independently do not influence each other s inheritance 3
Punnett Squares A A method of keeping track of all the possible combinations of alleles. Shows the possible offspring from two parents. A test cross: used to identify the genotype of an organism exhibiting a dominant trait. Create a dihybrid cross for the following genotypes and then answer the questions that follow: Cross: XYBb + XXbb Key: B: is dominant for brown eyes b: is recessive for blue eyes Questions: a). What is the probability of boys with blue eyes? b). What is the probability of girls with brown eyes? c). What is the genotype for girls with brown eyes? d). What is the genotypic ratio of girls with blue eyes? e). What is the phenotypic ratio of boys with Brown eyes? f). What is the genotype of a homozygous recessive (for eye color) male? g). What is the phenotype of the following genotype XXBb? h). How many gametes are formed as a result of meiosis? Punnett Squares Genetics Problems Beyond Dominant and Recessive Alleles Incomplete Dominance When one allele is not completely dominant over another it is called incomplete dominance. In incomplete dominance, the heterozygous phenotype is between the two homozygous phenotypes. Incomplete Dominance Neither allele is completely dominant. The heterozygous genotype results in a phenotype that is in between the two homozygous phentotypes. Example: Red snapdragons are crossed with white snapdragons. All the offspring will be pink. Beyond Dominant and Recessive Alleles - A cross between red (RR) X white (WW) - pink-colored flowers (RW). WW RR Incomplete Dominance Neither allele is completely dominant. The heterozygous genotype results in a phenotype that is in between the two homozygous phentotypes. Example: Snapdragons Beyond Dominant and Recessive Alleles Codominance In codominance,, both alleles contribute to the phenotype. In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers. Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately. 4
Codominance For example: Erminette chickens Beyond Dominant and Recessive Alleles Multiple Alleles Genes that are controlled by more than two alleles are said to have multiple alleles. alleles. An individual can can t have more than two alleles. However, more than two possible alleles can exist in a population. A rabbit's coat color is determined by a single gene that has at least four different alleles. Page 139 Black and white feathers Blood: Type AB blood (both alleles are expressed-- IA and IB ) Beyond Dominant and Recessive Alleles Different combinations of alleles result in KEY the colors shown here. C= full color; dominant to all other alleles cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles Multiple Alleles ch hc ch,c ch Full color: Chinchilla: Himalayan: AIbino: cc c CC, c c,hcc, or cch chcc ch,hor, orcch Cc c Human Skin Color controlled by 3 separately inherited genes Dominant Alleles: A, B, C (dark color) Recessive Alleles: a, b, c (light color) Some possible Genotypes: AABBCC very dark skin Examples: Coat color in rabbits and the human blood group Beyond Dominant and Recessive Alleles Traits Examples: Coat color in rabbits and the human blood group Blood Type Alleles IA i IB Polygenic Traits Polygenic Inheritance: 2 or more genes affect a single phenotype. Inheritance can be complicated and there is usually a wide range of phenotypes Examples: Feather color in parakeets, fur color in many mammals & Human skin color AaBbCc intermediate Aabbcc very light skin Alleles: A gene that has more than two alleles. Traits controlled by two or more genes are said to be polygenic traits. Skin color in humans is a polygenic trait controlled by more than four different genes. Alleles: A gene that has more than two alleles. c = albino; no color; recessive to all other alleles Polygenic Inheritance Inheritance skin color Multiple Polygenic Multiple ch = Himalayan; color in certain parts of the body; dominant to c allele Multiple Alleles & Polygenic Traits 2 Genes: (a) Color deposited (?) C color (b) Color of fur Genetic Disorders Genetic alleles Disorders: most are caused by recessive 1. Albinism Albinism:: these individuals are unable to produce melanin, the pigment responsible for skin color. 2. Sickle cell anemia: anemia: the shape of red blood cells are changed 3. Huntington disease: disease: caused by a dominant allele located on chromosome #4. Most people with this disorder have no symptoms until their late 30 30 s. They begin to lose control of their muscles, the nervous system breaks down and they usually die within 15 years. B black 5
Genetic Disorders (Continued) 4. Turner syndrome: : sex chromosomes fail to separate in meiosis. Females only, 45 X, there is a missing X chromosome 5. Klinefelter syndrome: : sex chromosomes fail to separate in meiosis. Males only, 47 XXY, there is an extra X chromosome http://gslc.genetics.utah.edu/units/disorders /karyotype/ (other) http://bluehawk.monmouth.edu/~bio/karyot ypes.htm (use this for making karyotype) Blood Relatives If you marry a first cousin and decide to have kids, your offspring would be homozygous for one-sixteenth of all their genes. Why: they share a common set of grandparents. So by probability one of every eight of your alleles would be identical. *we all carry a number of harmful alleles, which aren t expressed in the heterozygous condition. What is it that makes a person unique and different? Genetics Experiences Ethology: is the study of animal behavior The argument between nature and nurture is a debate as to which affects behavior. In reality, biologists study to what degree each factor impacts an organism. The End Rule of Multiplication & Probability What is the chance that two coins tossed simultaneously will land heads up? What is the probability of rolling two number 3 with dice? PP X pp: What is the probability of the offspring being Pp Pp X Pp: What is prob of Pp Pp X Pp: What is prob of pp Pp X Pp: What is the prob of pp Nature vs. Nurture Innate behavior: is programmed into our genes and is constant in any environment. (Nature - genes) Learned behavior: behavior is a response to what has been learned or experienced. (Nurture - environment) dihybrid crosses: YyRr(Parent) What is the probability that the gamete will carry the Y and R alleles? - What is the probability of an F2 plant having the genotype YYRR? Rule of Addition What is the probability that an F2 plant from a monohybrid cross will be heterozygous? Pp X Pp Trihybrid cross: PpYyRr X Ppyyrr Calculate the fraction of offspring which exhibit the recessive phenotypes for at least two of the three traits. List all the genotypes that fulfill this condition: ppyyrr, ppyyrr, Ppyyrr, PPyyrr, and ppyyrr ppyyrr: pp(1/4) yy(1/2) Rr(1/2) = 1/16 * once you do that for all of them then you simply pool all the probabilities. Karyotype Karyotype: is a picture of chromosomes used to identify genetic disorders. Animated karyotype Karyotype 6
How Do You Classify Chromosomes? Three main ways: 1) Length 2) Banding 3) Centromere position Online example Two different types of chromosomes 2) Sex chromosomes : X and Y chromosomes (1 pair) 1) Autosomes : all other chromosomes (22 pairs) Prenatal Screening for Genetic Disorders Amniocentesis: Removal and examination of fluid from the sac surrounding the fetus. Chorionic villus sampling (CVS): Removal and examination of tissue surrounding the fetus. Mutations Mutation: a change in the genetic information of a cell that is inheritable. How many genes do you think humans have? There are 2 different types of mutations: Chromosomal Mutations Gene Mutations Are mutations always harmful? Chromosomal Mutations Deletion : Part of the chromosome is missing Translocation: A missing piece from one chromosome attaches to a different chromosome Chromosomal Mutations Duplication: Part of the chromosome is repeated within the same chromosome Inversion The order of the chromosome is changed around Nondisjunction Gene Mutations Point Mutations: Nucleotide bases are switched Example: Instead of AATCGG, it would be AATTGG Frameshift Mutations: Deletion: nucleotide bases are missing Example: Instead of AATCGG, it would be AAGG Insertion: nucleotide bases are added Example: Instead of AATCGG, it would be AATTGCGG What part of protein synthesis would be impacted the most? Online Karyotype Activity Diagnosing http://www.biology.arizona.edu/human_bio/acti vities/karyotyping/karyotyping.html Chapter 13 Terms List H er edity: V ar iation: Genetics: Genes: Locus: DNA : Nucleic A cid: A sexual reproduction vs. sexual reproduction Genetics Problems Give an example of an or ganism that pr oduces a clone? M eiosis: T /F chromosomes are arranged r anged in pairs, with the largest pair being chromsome 1 and the smallest pairs being chromosome 23? If a per son has two X chr omosomes they would be males? T /F Kar yotype: Sex chromosomes: A utosomes: T /F sex cells have 222 autosomes and one sex chromosome? T /F sperm cells determine the sex of the offspring? Haploid cell has how many chromosomes? Diploid cell has how many chromosomes? If a cell in the testies with 24 chromosomes divides through meiosis: H ow many daughter cells will be produced? H ow many chromosomes will each daughter cell have? Compare and contrast mitosis with meiosis: p234 How do we get genetic variation: Why aren t we identical to our br other s and sister s, since we both have the same par ents shouldn t we be identical? Independent A ssortment of chromosomes: C rossing Over : Random Fertilization: 7
Terms Alleles: : the different forms of a gene Ex. The gene which determines height in pea plants has two different alleles: one will produce a tall plant the other produces a short plant. Dominant allele: : the expressed allele, expressed 3/4 of the time Recessive allele: : the non-expressed allele, expressed 1/4 the time. Example on page 127 Phenotype: : is the form of a trait that it displays genotype: : and organisms genetic composition homozygous: : organism which have an identical pair of alleles for a trait (tt or TT) heterozygous: : organism which have a mixed pair of alleles (Tt) segregation: : a process which separates the two alleles of a gene Multiple alleles: : is a type of gene that is determined by more Multiple Alleles Blood Type Is determined by the antigens found on the surface of red blood cells. Antigen: : Proteins which stimulate the production of antibodies. Why must blood types match in order to transfer. Multiple Alleles: : More than two forms of the same gene which governs the same trait. Alleles: : Two forms of the same gene which govern the same trait. Three alleles responsible for determining blood type: A, B, O What are the different phenotypes for blood? Possible genotypes: Is it possible for parents with the following blood types(ab&bo) to have offspring with O type blood? What is the rarest blood type? 38% will have group O positive blood. 7% will have group O negative blood. 34% will have group A positive blood. 6% will have group A negative blood. 9% will have group B positive blood. 2% will have group B negative blood. 3% will have group AB positive blood. 1% will have group AB negative blood. Rh Factor: Rh+: There are additional antigens associated with the red blood cells Rh-: No additional antigens Ertoblastosis fetalis: Mother (Rh-) Father (Rh+) -------- Baby (Rh+) Some of the babies blood passes into the mothers, antibodies are produced which pass into the fetus and destroy its red blood cells: Limiting oxygen. Usually 8
Dependent or Independent Segregation Probability The probability scale ranges from 0-1. An event that is certain to happen has a probability of 1. An event that is certain not to occur has a probability of 0. With a two headed coin what is the probability of tossing heads? With a normal coin what is the probability of tossing heads? What is the probability of rolling a 3 with a six sided die? The probabilities of all possible outcomes for an event must add up to 1. With a die, the chance of rolling a number other then 3 is? The outcome of any particular toss is unaffected by what has happened on previous trials. Probability Epistasis A A gene at one locus alters the phenotypic expression of a gene at a second locus. Epistasis Explain what is going on here. Pleiotropic effects of the sickle- cell allele Pleiotropy: Most genes have multiple phenotypic effects. Remember there are only 33,000 genes. Mutations Rule of Multiplication & Probability What is the chance that two coins tossed simultaneously will land heads up? What is the probability of rolling two number 3 with dice? PP X pp: What is the probability of the offspring being Pp Pp X Pp: What is prob of Pp Pp X Pp: What is prob of pp Pp X Pp: What is the prob of pp dihybrid crosses: YyRr(Parent) What is the probability that the gamete will carry the Y and R alleles? - What is the probability of an F2 plant having the genotype YYRR? 9