3.a.3 – The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring (14.1-14.4). 4.c.2 – Environmental factors influence the expression of the genotype in an organism – (14.3). 4.c.4 – The diversity of species within an ecosystem may influence the stability of the ecosystem (14.3). 1. Blending Theory - traits were like paints and mixed evenly from both parents 2. Incubation Theory - only one parent controlled the traits of the children Ex: Spermists and Ovists 3. Particulate Model - parents pass on traits as discrete units that retain their identities in the offspring Father of Modern Genetics Mendel’s paper published in 1866, but was not recognized by science until the early 1900’s Died prior to his “fame” Used an experimental approach (scientific method) Applied mathematics to the study of natural phenomena Ratios and probability Kept good records and observations Large test sample/size 1. 2. Short life span Bisexual *Both sexes in one flower/plant *Stamens and carpels 3. Many traits known *Easy to see/observe traits 4. Cross- and self-pollinating *Easy to control reproduction 5. You can eat the failures Cross between two different parents Results in hybrid offspring ◦ The offspring may be different than the parents. Cross with only one flower ◦ Stamens/carpels fertilize each other! Naturally occurring event in pea plants Results in pure-bred offspring where the offspring are identical to the parents Is this asexual reproduction??? NO…you still have gametes Used seven characters, each with two expressions or traits Example: ◦ Character - height ◦ Traits - tall or short Mono = one Crosses that work with a single character at a time ◦ Example - Tall X short The Parental generation or the first two individuals used in a cross ◦ Example - Tall X short Mendel used reciprocal crosses, where the parents alternated for the trait F1 - first filial generation ◦ Filial – Latin for “son” F2 - second filial generation, ◦ Bred by crossing two F1 plants together or allowing a F1 to self-pollinate Notice: TWO P1 plants shown (cross fertilz.) Notice: only ONE plant shown (self-fertilz.) P1 F1 F2 Tall X short (TT x tt) all Tall (Tt) 3 tall to 1 short (1 TT: 2 Tt: 1 tt) Tall Short Mendel observed SAME pattern in ALL 7 characters ◦ F1 generation showed only one of the traits (regardless of sex) ◦ The other trait reappeared in the F2 at ~25% 3:1 ratio; 3 dominant – 1 recessive Remember: the % are estimates (still have mutations that could change %) 1. 2. Genes can have alternate versions called alleles Each offspring inherits two alleles, one from each parent He made this conclusion without having knowledge of chromosomes/DNA makeup ** Remember: Each diploid cell has a pair of homologous chromosomes -Therefore, any gene has 2 loci *one on maternal chromo *one on paternal chromo 3. If the two alleles differ, the dominant allele is expressed The recessive allele remains “hidden” (unseen) unless the dominant allele is absent Now called Mendel’s Law of Dominance 4. The two alleles for each trait separate during gamete formation (meiosis) This now called Mendel's Law of Segregation Phenotype - the physical appearance of the organism Genotype - the genetic makeup of the organism, usually shown in a code ◦ T = tall ◦ t = short Homozygous - When the two alleles are the same (TT/tt) Heterozygous- When the two alleles are different (Tt) Notice (for single-gene traits: ◦ Three choices for genotypes ◦ Homo Dom (TT), Homo Rec (tt), Hetero (Tt) Cross TT X tt Tt X Tt TT X TT tt X tt TT X Tt Tt X tt Genotype all Tt 1TT:2Tt:1tt all TT all tt 1TT:1Tt 1Tt:1tt Phenotype all Dom 3 Dom: 1 Res all Dom all Res all Dom 1 Dom: 1 Res Notice the 3:1 ratio!!! Cross of a suspected heterozygote with a homozygous recessive ◦ Goal: to determine genotype of unknown Ex: T? X tt *If TT - all Dominant *If Tt - 1 Dominant: 1 Recessive Cross with two genetic traits ◦ Di = two Need 4 letters (two for each trait) to code for the cross ◦ Ex: TtRr (Mono = Tt OR Rr) Each Gamete - Must get 1 letter for each trait ◦ Ex. TR, Tr, etc. (when combine = 4 letters) Critical to calculating the results of higher level crosses Look for the number of heterozygous traits The formula 2n can be used, where “n” = the number of heterozygous traits. Ex: TtRr, n=2 (2 heterozygous traits) ◦ 22 or 4 different kinds of gametes are possible (TR, tR, Tr, tr) Ex: TtRR, n = ? ◦ 21 or 2 different gametes are possible TtRr X TtRr Each parent can produce 4 types of gametes. (n=2; 22=4) ◦ TR, Tr, tR, tr Cross is a 4 X 4 = 16 possible offspring 9 3 3 1 Tall, Red flowered Tall, white flowered short, Red flowered short, white flowered Or: 9:3:3:1 ratio The inheritance of 1st genetic trait is NOT dependent on the inheritance of the 2nd trait ◦ Ex: Inheritance of height is independent of the inheritance of flower color This relates to dihybrid crosses – one character’s inheritance is NOT connected to the inheritance of another! Ratio of Tall to short is 3:1 Ratio of Red to white is 3:1 The cross is really a product of the ratio of each trait multiplied together. (3:1) X (3:1) = 9:3:3:1 ◦ *Use FOIL method to attain ratio Genetics is a specific application of the rules of probability Probability - the chance that an event will occur out of the total number of possible events The monohybrid “ratios” are actually the “probabilities” of the results of random fertilization Ex: 3:1 75% chance of the dominant 25% chance of the recessive The probability that two alleles will come together at fertilization, is equal to the product of their separate probabilities Steps to determining probability: ◦ 1) Determine ratios for each character/trait How? Do “little” Punnett squares for EACH trait ◦ 2) Multiply ratios together The probability of getting a tall offspring is ¾. The probability of getting a red offspring is ¾. (use same Punnett square as above – only with R/r) The probability of getting a tall red offspring is ¾ x ¾ = 9/16 Use the Product Rule to calculate the results of complex crosses rather than work out the Punnett Squares Ex: TtrrGG X TtRrgg TtrrGG X TtRrgg “T’s” = Tt X Tt = 3:1 “R’s” = rr X Rr = 1:1 “G’s” = GG x gg = 1:0 Product is: (3:1) X (1:1) X (1:0 ) = 3:3:1:1 1. 2. 3. 4. 5. Incomplete Dominance Codominance Multiple Alleles Epistasis Polygenic Inheritance When the F1 hybrids show a phenotype somewhere between the phenotypes of the two parents Ex. Red X White snapdragons F1 = all pink F2 = 1 red: 2 pink: 1 white NOT BLENDING!!!!! Not enough red pigment made No hidden recessive 3 phenotypes and 3 genotypes (Hint! – often a “dose” effect) ◦ Red = CR CR ◦ Pink = CRCW ◦ White = CWCW Both alleles are expressed equally in the phenotype NOT an intermediate (like incomplete dominance Ex. MN blood group ◦ MM, MN, NN Ex: Rooster/chicken feathers Ex: flower petal color No hidden recessive 3 phenotypes and 3 genotypes (but not a “dose” effect) When there are more than 2 alleles for a trait ◦ *Remember: only 2 alleles exist for Mendel’s pea plants Ex. ABO blood group ◦ IA - A type antigen ◦ IB - B type antigen ◦ i - no antigen Multiple genotypes and phenotypes Very common event in many traits Phenotypes A B AB O Genotypes IA IA or IAi IB IB or IBi IAIB ii IA and IB are dominant A and B are CODOMINANT A and B are the names for two different carbohydrates found on the surface of RBCs ◦ Blood types are actually ways of differentiating the type of antigens on a person's red blood cells Rh blood factor is a separate factor from the ABO blood group Rh+ = dominant Rh- = recessive Wife is type A Husband is type AB Child is type O Question - Is this possible? Comment - Wife’s boss is type O…There’s some explaining to be done! Factors that are expressed as continuous variation Lack clear boundaries between the phenotype classes Ex: skin color, height Several genes govern the inheritance of the trait Ex: Skin color is likely controlled by at least 4 genes ◦ Each dominant gives a darker skin Mendelian ratios fail Traits tend to "run" in families Offspring often intermediate between the parental types Trait shows a “bell-curve” or continuous variation Often done by Pedigree charts Why? ◦ Can’t do controlled breeding studies in humans ◦ Small number of offspring ◦ Long life span Male Female Person with trait Dominant Trait Recessive Trait Several thousand known! Some examples: ◦ Albinism ◦ Sickle Cell Anemia ◦ Tay-Sachs Disease ◦ Cystic Fibrosis ◦ PKU ◦ Galactosemia Most common inherited disease among African-Americans Single amino acid substitution results in malformed hemoglobin Reduced O2 carrying capacity Codominant inheritance Only affects Eastern European Jews Brain cells unable to metabolize type of lipid; accumulation of the lipid causes brain damage Death in infancy or early childhood Most common lethal genetic disease in the U.S. Most frequent in Caucasian populations (1/20 a carrier) Produces defective chloride channels in membranes Usually rare Skips generations Occurrence increases with consaguineous matings (people descended from the same ancestor) Often an enzyme defect Affects males and females equally Less common then recessives Affects males and females equally Ex: ◦ Huntington’s disease ◦ Achondroplasia ◦ Familial Hypercholesterolemia Each affected individual had one affected parent. Doesn’t skip generations. Homozygous cases show worse phenotype symptoms. May have post-maturity onset of symptoms. Blood tests for recessive conditions that can have the phenotypes treated to avoid damage Genotypes are NOT changed Ex: PKU ◦ Required by law in all states ◦ Tests 1- 6 conditions ◦ Required of “home” births too Where Genetic and Environment Factors interact to cause the disease Ex: Heart Disease factors ◦ ◦ ◦ ◦ Genetics Diet Exercise Bacterial infections Recognize Mendel's experiments and their role in the scientific discovery of genetic principles. Identify Mendel's Laws of Genetics. Recognize the use and application of probability in genetics. Recognize the basic Mendelian crosses and genetic terminology. Recognize various extensions of Mendelian genetics and their effect on inheritance patterns. Identify human traits that exhibit Mendelian inheritance patterns. Recognize methods used in genetic screening and counseling.