WHY MENDEL SUCCEEDED Gregor Mendel (1822-1884) Austrian Monk known as the “father of modern genetics” Found that inheritance follows certain laws later known as Mendel’s Laws of Inheritance Heredity is the passing on of characteristics from parent to offspring Inherited characteristics are called traits (factors) The branch of biology that studies heredity is called genetics – which was founded upon the rediscovery of his work.
WHY MENDEL SUCCEEDED Mendel’s pea plant collection contained around 28,000 plants Pea plants reproduce sexually by producing male and female sex cells (gametes) Male gamete forms in pollen Female gamete formed in ovary Fertilization occurs when the male gamete unites with the female gamete Pollination is the transfer of pollen to ovary in a plant – normal reproduction. Remove male parts Snipping the stamen could prevent self-pollination
Flower parts Quickly sketch and label this diagram A similar figure is in the book on pg. 642
WHY MENDEL SUCCEEDED Cross-pollination is transferring pollen of one plant to the ovary of another plant Mendel did this to get certain plants to breed with others to be sure of the parents Mendel was very careful with all of his work Figure 10.1
Mendel was able to create tall plants and short plants (purebreds) He referred to the offspring of a purebred tall and a purebred short as a hybrid Crossing a 6’ tall plant with a 2’ tall (short) plant resulted in all 6’ tall plants Crossing the hybrid offspring resulted in 75% tall and 25% short P 1 refers to the “Parental generation” F 1 (“Filial”) refers to the offspring Tall pea plant All tall pea plants 3 tall: 1 short P1P1 MENDEL’S MONOHYBRID CROSSES F1F1 F2F2 Figure 10.2 Short pea plant
MENDEL’S MONOHYBRID CROSSES So what does MONOHYBRID refer to? Referring to figure 10.3: When Mendel crossed a purebred tall with a purebred short he got all tall plants When he crossed a purebred purple flower with a purebred white flower he got all purple flowers He referred to the trait that was observed in these cases as dominant The trait that seemed to “disappear” he called recessive Law of Dominance Mendel concluded that these plants have “factors” that control each of the traits (color, shape, height) We call these factors genes (parts of DNA) Alternative forms of genes (tall vs. short or yellow vs. green) are known as alleles.
Recessive trait Dominant trait Seed shape Seed color Flower color Flower position Pod color Pod shape Plant height roundyellowpurple axial (side) green inflated tall wrinkledgreenwhite terminal (tips) yellow constricted short Figure 10.3
Below is a list of human traits, write them down. Widow’s peakTongue Rolling DimplesMid-digit Hair Free Ear LobesStraight Thumb FrecklesBent Pinky Finger Are they dominant or recessive? (Take a guess) HUMAN TRAITS
TT MENDEL’S MONOHYBRID CROSSES These two alleles for each trait can be expressed as a single letter For plant height we can use the letters “T” & “t” Dominant allele is “T” Recessive is “t” Mendel’s purebred tall plants were “TT” His purebred recessive plants were “tt” Fill in the blanks in the figure to the right which t goes where? Tall plant Short plant All tall plants F1F1 TTtttT P1P1
TT MENDEL’S MONOHYBRID CROSSES Mendel concluded that the allele (gene form) of tall plants was dominant to the allele for short plants Confirming that the plants had two alleles for each trait (TT = Tall, Tt = Tall, or tt = short) Knowing that traits are inherited from parents, he also concluded that these alleles are inherited However a plant can only get one allele from each parent The gametes (sex cells) contained either one or the other form of the gene (T or t) The Law of Segregation states that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles.
PHENOTYPES AND GENOTYPES Phenotype refers to the organism’s physical characteristic (what you can see) Ex: Tall Genotype refers to the organism’s genetic makeup (what you can’t see) Ex: TT or Tt Homozygous represents two alleles that are the same (TT or tt) Heterozygous organisms have different alleles (Tt) How are we going to distinguish Homo and Hetero?
PUNNETT SQUARES 1905 - Reginald Punnett devised an easy way to find expected genotype proportions of offspring from known parent genotypes based off Mendel’s laws Heterozygous tall parent T Tt T t t TTTt tt Heterozygous tall parent tT t t t T T T G= 50% Tt : 25% TT : 25% tt P= 3 Tall : 1 short Monohybrid Cross (one trait)
PUNNETT SQUARES Monohybrid crosses are easy to separate alleles according to Mendel’s Law of Segregation If we have heterozygous parents (Tt X Tt) we can just separate the T from the t For Dihybrid crosses, the gamete separation is a little tricky If we have two parents that are heterozygous for seed shape (Rr) and seed color (Yy) their genotype is RrYy To separate alleles into gametes we use the FOIL method from algebra RrYy makes four different gametes Using the FOIL method we get… RYRyrYry Round Yellow Round green wrinkled Yellow wrinkled green
MENDEL’S DIHYBRID CROSSES Mendel also crossed plants with two different traits Round=R, wrinkled=r & Yellow=Y, green=y What is the genotype of a purebred (homozygous) plant with Round Yellow seeds? What is the genotype of a purebred (homozygous) plant with wrinkled green seeds? Purebred (homozygous) Round Yellow seeds X Purebred (homozygous) wrinkled green seeds Result of F 1 …All plants had Round Yellow seeds However crossing the F 1 gives a 9:3:3:1 ratio Which leads us to Mendel’s second law… The Law of Independent Assortment states that genes for different traits are inherited independently of each other. RRYY rryy
Round Yellow (RRYY) X wrinkled green (rryy) Round Yellow wrinkled green All Round Yellow Round YellowRound greenwrinkled Yellow wrinkled green 933 1 P1P1 F1F1 F2F2 R_Y_ R_yy rrY_ rryy
Gametes from RrYy parent RYRy ry rY RY Ry rY ry RRYY RRYy RrYYRrYyRRYy Rryy RrYY Rryy RrYy rrYYrrYy RrYy RRyy rrYyrryy Gametes from RrYy parent Starting here what are the gametes?
PROBABILITY Knowing the parents genotype we can predict the probable offspring genotype and phenotype What is the probability of having Rr offspring? What is the probability of having Round offspring? R r R r RRRr rr 75% 50%
PROBABILITY Given the parents genotype and number of offspring, you should be able to predict the number of each genotype and phenotype. PROBABILITY PROBLEM R=Round seeds & r=wrinkled seeds 1. P 1 genotype: RR X rr 2. All of the F 1 offspring will be ______. 3. Assume 140 F 2 offspring are created from F 1. 4. ________ will have their parents (F 1 ) genotype. 5. ________ will have Round seeds. 6. ________ will have wrinkled seeds. 7. ________ will have the same genotype as the P 1.
PROBABILITY PROBLEM (#2) Rr (Round) 2. All of the F 1 offspring will be ______. P 1 =RR X rr (always put first parent on top of square) RR r r Rr 2. All of the F 1 offspring will be ___________.
PROBABILITY PROBLEM (#4) 70 4. ________ will have their parents (F 1 ) genotype. F 1 = All Rr Rr R r RRRr rr 4. ________ will have their parents (F 1 ) genotype. # of F 2 Offspring = _____ Expected % of genotype (Rr) that is same as parents= ______ 50% (2/4) of 140 = _____ 140 X.5 = 70 140 50% 70
PROBABILITY PROBLEM (#5) 105 5. ________ will have Round seeds. Rr R r RR Rr rr 5. ________ will have Round seeds. # of F 2 Offspring = _____ Expected % of Round phenotype = ______ 75% (3/4) of 140 = _____ 140 X.75 = 105 140 75% 105
PROBABILITY PROBLEM (#6) 35 6. ________ will have wrinkled seeds. Rr R r RR Rr rr 6. ________ will have wrinkled seeds. # of F 2 Offspring = _____ Expected % of wrinkled phenotype = ______ 25% (1/4) of 140 = _____ 140 X.25 = 35 140 25% 35
PROBABILITY PROBLEM (#7) 70 7. ________ will have the same genotype as the P 1 (RR or rr). Rr R r RR Rr rr 7. ________ will have the same genotype as the P 1. # of F 2 Offspring = _____ Expected % of RR or rr genotype = ______ 50% (2/4) of 140 = _____ 140 50% 70