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More Mendelian genetics

More Mendelian genetics. Real Biologists of Genius. We salute you Mr. Gregor Mendel. An Austrian monk with a love for peas, you published data that showed blending inheritance was incorrect and introduced hereditary factors occurring in discrete pairs. Mendelian Genetics.

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More Mendelian genetics

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  1. More Mendelian genetics

  2. Real Biologists of Genius • We salute you Mr. Gregor Mendel. An Austrian monk with a love for peas, you published data that showed blending inheritance was incorrect and introduced hereditary factors occurring in discrete pairs.

  3. Mendelian Genetics • Mendel knew that his 'factors' were discrete and non-blending.  • He also knew much more about the behavior of these units of inheritance. • So let’s revisit his peas!

  4. Mendel's First Law (Law of Segregation): Mendel determined that each individual has two copies of each gene (e.g., Pp). These copies are called alleles.  If both alleles are the same, then the individual is homozygous (e.g., PP or pp).  If the two alleles are different, then the individual is heterozygous (e.g., Pp). When an individual creates gametes (sex cells: egg or sperm in humans, egg or pollen grain in plants), only one of each allele is packaged in the gamete.  Mendel determined that which allele appears in the gamete is random, with each allele having a 50% chance.  This rule is the Law of Segregation. Law of Segregation

  5. Flower color • Pea flowers are either purple or white. • Peas fertilize themselves, so • white  white and purple  purple. • called true-breeding • But…

  6. …if you cross a true-breeding purple with a true-breeding white… • …all of the offspring have purple flowers. • Hence Mendel said that purple was dominant to white. • PP: purple • pp: white • Pp: purple!

  7. gene: stretch of DNA that codes for a particular trait. (e.g., flower color) allele: a particular variant of a gene (e.g., purple) genotype: what alleles an individual has for a particular trait or set of traits (e.g., Pp) phenotype: the expression of the genes; what the individual looks like (e.g., purple) dominant trait: an allele that is expressed no matter what the other allele is (e.g., purple flower color being dominant to white flower color in pea plants) recessive trait: an allele that is only expressed if it is the only allele present (i.e., both alleles are the same) (e.g., white flower being recessive to purple flower color) Terms to understand

  8. homozygous: has 2 copies of the same allele for a given trait (e.g., PP or pp) heterozygous: has 1 copy of each of two alleles for a given trait (e.g., Pp) F1 generation: the kids of the parents F2 generation: the grandkids of the parents (kids of F1) gamete: sex cell (egg or sperm); only has ONE allele for each gene since it only has one homologous chromosome (either the one you received from Mom or the one you received from Dad) True-breeding: homozygous for the trait. Terms to understand

  9. How many different gametes can PP make? 1 P How many different gametes can Pp make? 2 P or p When forming gametes, you always need one allele for each gene. How many different gametes can PPTt make? 2 PT or Pt Forming gametes

  10. AaBBCc? 2 x 1 x 2 = 4 AaBbCC? 2 x 2 x 1 = 4 AaBbCcDd? 2 x 2 x 2 x 2 = 16 AAbbCCddEE? 1 x 1 x 1 x 1 x 1 = 1 What is it? AbCdE Which of the following gametes can this parent (AABbCCDdeeFf) make? a. AAbCEf b. ABCDEF c. abcdef d. ABCdef d is the answer. What is the chance of that parent producing that gamete? 1/8 Why? Determining the number of different gametes possible

  11. AaBBCc? 2 + 1 + 2 = 5 alleles AaBbCC? 2 + 2 + 1 = 5 alleles AaBbCcDd? 2 + 2 + 2 + 2 = 8 AAbbCCddEE? 1 + 1 + 1 + 1 + 1 = 5 How many different genes are shown at right? 3, 3, 4, and 5 (top to bottom) Determining the number of different alleles

  12. Incomplete dominance: in this case, the presence of a single gene to code for a particular protein (enzyme) is insufficient to produce the full trait. Why? Because you don’t have enough of the enzyme to fully express the trait! Ex. In snapdragons, RR = red, rr = white, Rr = pink! Other terms not on the handout

  13. Incomplete Dominance

  14. There are 2 dominant alleles (A and B) and one recessive (O). A and B alleles determine sugars present on cell membrane of red blood cells. If you have A, then you produce type A sugars. If you have B, then you produce type B sugars. If you have O, then you produce no sugars. Possible Possible GenotypesPhenotypes AA type A AO type A BB type B BO type B AB type AB OO type O Co-dominant alleles: Human ABO blood type

  15. When you need a blood transfusion, they try to match blood types. If you give type A blood to someone without type A blood, they have no type A blood sugars on their own red blood cells so their immune system will attack the transfused blood because it recognizes that it is foreign.  While they try to give type A blood to a person with blood type A, type O could also be used. Why? Because there are no blood sugars in type O blood that the type A person’s body hasn’t seen. Therefore, type O is called the universal donor and type AB is the universal recipient. Transfusions

  16. What about positive and negative? • That’s a different gene. • The Rh factor is another sugar on red blood cells. • It’s called Rh for Rhesus, as it was first found in a Rhesus monkey. • You are Rh positive if you have the blood sugar, but Rh negative if you do not. • Thus the ultimate donor is? • O negative • Ultimate recipient? • AB positive

  17. What are the relative frequencies of these blood types in humans? • O Positive 37% • O Negative 6% • A Positive 34% • A Negative 6% • B Positive 10% • B Negative 2% • AB Positive 4% • AB Negative 1%

  18. Some More Terms • Monohybrid cross: cross between two monohybrids (only a single trait is tracked) (e.g., Pp x Pp) • Dihybrid cross: cross between two dihybrids (e.g., PpYy x PpYy). Dihybrid Cross

  19. Some More Terms • Pleiotropic: when a single gene determines more than one phenotype for an organism (gene that lengthens bones lengthens legs and arms). • Gene for sickle cell affects vulnerability to malaria and sickle cell anemia.

  20. Polygenic traits • A trait that is affected by multiple genes • These traits are not discrete (yes or no) but show continuous variation. • E.g. skin color, height, etc.

  21. Test Cross • Test cross: When a single trait is being studied, a test cross is a cross between an individual with the dominant phenotype but of unknown genotype (homozygous or heterozygous) with a homozygous recessive individual. If the unknown is heterozygous, then approximately 50% of the offspring should display the recessive phenotype.

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