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Section 10.1

Section 10.1. Unit 7 Mendel’s Laws of Heredity. pg. 253. WHY MENDEL SUCCEEDED. 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. Gregor Mendel (1822-1884)

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Section 10.1

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  1. Section 10.1 Unit 7 Mendel’s Laws of Heredity pg. 253

  2. WHY MENDEL SUCCEEDED 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. 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 ________________ is the passing on of characteristics from parent to offspring

  3. 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. Cross-pollination is transferring pollen of one plant to the ovary of another plant

  4. Figure 10.2 P1 MENDEL’S MONOHYBRID CROSSES Short pea plant Tall pea plant 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 P1 refers to the “Parental generation” F1 (“Filial”) refers to the offspring F1 All tall pea plants F2 3 tall: 1 short

  5. MENDEL’S MONOHYBRID CROSSES So what does MONOHYBRID refer to? Referring to figure 10.3 (next slide): 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 __________________ The trait that seemed to “disappear” he called ________________ Mendel concluded that these plants have “factors” that control each of the traits (color, shape, height) We call these factors genes (parts of DNA that code for a protein) Alternative forms of genes (tall vs. short or yellow vs. green) are known as alleles.

  6. Plant height Figure 10.3 Seed shape Seed color Flower color Flower position Pod color Pod shape Dominant trait axial (side) round yellow purple green inflated tall Recessive trait terminal (tips) wrinkled green white yellow short constricted

  7. P1 MENDEL’S MONOHYBRID CROSSES Tall plant Short plant 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 _____ Recessive is _____ Mendel’s purebred tall plants were “TT” His purebred recessive plants were “tt” Fill in the blanks in the figure to the right which Tt goes where? F1 All tall plants

  8. 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 _________________________ states that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles.

  9. PHENOTYPES AND GENOTYPES _______________ refers to the organism’s physical characteristic (what you can see) Ex: Tall __________________ refers to the organism’s genetic makeup (what you can’t see) Ex: TT or Tt ____________________________ represents two alleles that are the same (TT or tt) ____________________________ organisms have different alleles (Tt) Law of ___________________ states that hybrid organisms (Tt) will express the dominant allele (ex: tall).

  10. Monohybrid Cross (one trait) PUNNETT SQUARES Heterozygous tall parent T t T t T t 1905 - Reginald Punnett devises an easy way to find expected genotype proportions of offspring from known parent genotypes based off Mendel’s laws T T t t t T t G= 50% Tt : 25% TT : 25% tt Heterozygous tall parent P= 3 Tall : 1 short

  11. TWO TRAIT PUNNETT SQUARES Round Yellow Round green 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… wrinkled Yellow wrinkled green

  12. 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 F1…All plants had Round Yellow seeds However crossing the Dihybrid F1 gives a ratio of ___________ Which leads us to Mendel’s third law… The Law of ___________________________ states that genes for different traits are inherited independently of each other.

  13. Round Yellow (RRYY) X wrinkled green (rryy) P1 wrinkled green Round Yellow F1 All Round Yellow F2 9 3 3 1 Round Yellow Round green wrinkled Yellow wrinkled green R_Y_ rrY_ R_yy rryy

  14. Gametes from RrYy parent Starting here what are the gametes? ry RY Ry rY RY RRYY RRYy RrYY RrYy Ry Gametes from RrYy parent RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy

  15. % PROBABILITY % r R RR Rr R 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? Rr rr r

  16. 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. P1 genotype: RR X rr 2. All of the F1 offspring will be ______. 3. Assume 140 F2 offspring are created from F1. 4. ________ will have their parents (F1) genotype. 5. ________ will have Round seeds. 6. ________ will have wrinkled seeds. 7. ________ will have the same genotype as the P1.

  17. R R PROBABILITY PROBLEM (#2) Rr Rr r 2. All of the F1 offspring will be ______. P1=RR X rr (always put first parent on top of square) Rr Rr r 2. All of the F1 offspring will be ___________.

  18. R r # of F2 Offspring = _____ Expected % of genotype (Rr) that is same as parents= ______ 50% (2/4) of 140 = _____ 140 X .5 = RR Rr PROBABILITY PROBLEM (#4) R Rr rr 4. ________ will have their parents (F1) genotype. F1= All Rr r 4. ________ will have their parents (F1) genotype.

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