CHAPTER 9 Fundamentals of Genetics

1. CHAPTER 9Fundamentals of Genetics Honors Biology Tyska Holliston High School

2. 9-1 Mendel’s Legacy • What is GENETICS? The scientific study of ________________ - how individuals inherit characteristics from their parents. • What is “Classical Genetics”? The study of heredity based on fundamental principles Mendel theorized in his experiments with pea plants.

3. WHO WAS GREGOR MENDEL?The “Father of Genetics” • Austrian monk born 1822  Studied statistics at the University of Vienna • 1853 – observed plants in monastery garden – experimented with pea plants • Studied 7 different traits each with contrasting characters • (ex) Height, short or tall

4. _______ = parental generation = original pair of plants • _______ = first filial generation= first generation • _________: offspring from parents with different traits

5. Working With Pea Plants • __________: plant’s sperm formed in anther • ____________: plants female eggs in stigma • Fertilization: joining of pollen + egg cells  develops into embryo in a seed • Mendel crossed the plants with contrasting characters and looked at their offspring

6. Mendel’s Experiments • _________________: pollen fertilizes egg cells in the SAME flower (single parent reproduction) • ____________________(Pure Strain): offspring genetically identical to parents due to self-pollination • ____________________: combining reproductive cells from 2 DIFFERENT parent plants Mendel could cross- breed a purple flower with a white flower… What do you think is the color of the offspring?

7. Tracking Generations • Parental generation _____ mates to produce • First-generation offspring _____ mate to produce • Second-generation offspring _____

8. CROSS-POLLINATION: Mendel cut the male parts (ANTHERS) of one flower (ouch!) and dusted the female parts (STIGMA) with pollen from another flower. P GENERATION: purple x white flowers F1 GENERATION: all purple flowers HYBRID PLANTS

9. What happened in Mendel’s crosses? All the offspring only had one of the parent’s characters…the other parent’s character disappeared!! Mendel’s Conclusions: • Inheritance is determined by factors that are passed down • _______: the factors that determine traits • Contrasting characters are different forms of a gene called _____________

10. Mendel’s Principle of Dominance • some alleles are dominant, some are recessive • _____________________________: form of trait that will always be exhibited; usually expressed in capitals • ______________________________: form of trait is only exhibited when the dominant allele is NOT present • (ex) Allele for tall is dominant for and the allele for short is recessive

11. What happened to the recessive allele? • Mendel wanted to know if the recessive allele disappeared from the F1 plants. • F1 CROSS: He self-crossed the F1 generations to make F2 offspring

12. THE F2 GENERATION… • The recessive traits reappeared!! • _____________plants had white flowers, the recessive trait • Summary of Crosses: tall plants X short plants  tall plants P P F1 tall plants self-pollinating  ¼ short, ¾ tall F1 Cross F2

13. Explaining the F1 Cross • Why did the recessive allele reappear? At some point, the recessive allele had to separate from the dominant allele. This is called… • _____________________________: separation of alleles during formation of gametes (eggs & sperm) in anaphase II of meiosis

14. Homozygous dominant parent Homozygous recessive parent Mendel’s Law of Segregation (chromosomes duplicated before meiosis) During gamete formation, the alleles segregate from each other meiosis I meiosis II (gametes) (gametes) fertilization produces heterozygous offspring

15. MENDEL’S LAWS THE LAW OF SEGREGATION • F1 plants inherited 1 tall allele & 1 short allele from parents • When gametes are formed, the two alleles segregate from each other  each gamete has 1 copy of each gene • So, 2 different types of gametes are formed (one w/ tall allele, one w/ short allele) THE LAW OF INDEPENDENT ASSORTMENT • Independent segregation of chromosomes/genes during the formation of gametes. • Genes do not influence each other’s inheritance • Accounts for genetic variation.

16. Law of Independent Assortment OR Metaphase I: A A a a A A a a B B b b b b B B Metaphase II: A A a a A A a a B B b b b b B B Gametes: B B b b b b B B A A a a A A a a 1/4 AB 1/4 ab 1/4 Ab 1/4 aB

17. Mendel’s Findings….today • MOLECULAR GENETICS:study of the structure and function of chromosomes and genes • GENE: segment of DNA on a chromosome that controls a particular hereditary trait; occurs in pairs • ALLELES: alternative forms of a gene; represented by letters • capital letters = dominant alleles (TT) • lower-case letters = recessive alleles (Tt)

18. 9-2 GENETIC CROSSES • Mendel realized that the principles of probability can explain the results of genetic crosses. • ________________________: likelihood an event will occur • Flip coin 3x in a row. What are the chances that it will be heads all three times? The pattern in which alleles segregate is random…just like a coin flip! So which ever allele gametes receive is also random

19. CALCULATING PROBABILITY # of times an event is expected to happen PROBABILITY = # of opportunities for an even to happen In the F2 generation, Mendel observed 705 purple flowers and 224 white flowers. Based on these numbers, what is the probability that the dominant trait will be expressed?

20. Punnett Squares What is a Punnett Square? • A diagram showing the possible genetic combinations from a particular cross • Can be used to predict and compare the genetic variations that will result from a cross ___________________________________: a cross between individuals that involves ONE pair of contrasting traits ___________________________________: a cross between individuals that involves TWO pairs of contrasting traits

21. Letters in a Punnett Square • Letters represent alleles: capital = dominantlowercase = recessive • _________________________: has two identical alleles for a trait (ex) TT or tt • _________________________: has two different alleles for the same trait (ex) Tt What would be the letters for a HOMOZYGOUS RECESSIVE individual? (use any letter)

22. Punnett Squarefor Tt x Tt Punnett Squarefor YY x yy heterozygous

23. Genotype vs Phenotype • _______________________: the genetic makeup of an organism (ex) TT • _____________________: the physical characteristics exhibitied (ex) tall plant • ____________________: fractions that appear in the offspring (genotypic or phenotypic ratios) What are the genotypic and phenotypic ratios of the offspring?

24. Practicing with Punnett Squares “LET” Statement: • _____ = round pea • _____ = wrinkled pea If a heterozygous pea is crossed with a wrinkled pea, what are the genotypic and phenotypic ratios of the offspring?

25. DIHYBRID CROSSES • TWO-FACTOR CROSSES: crossing 2 individuals that involves 2 pairs of contrasting traits EXAMPLE: (P Generation) • Two Genes: shape of pea & color of pea • The Cross: (R=round, Y=yellow) • Round yellow peas x wrinkled green peas __________ x __________

26. PRACTICING WITH DIHYBRID CROSSES • What are the possible alleles parent 1 can pass? __________ • What are the possible alleles parent 2 can pass? ____________ • F1 Generation =

27. F1 Cross: RrYy x RrYy • What are the possible allele combinations each parent can pass on? • 4 possible combinations: _____________________________ • Draw a Punnett Square for this cross.

28. The F2 Generation The F1 hybrid cross always produces a ___________phenotypic ratio

29. Test Cross • In guinea pigs, the trait for a black color coat (B) is dominant to brown (b). If a guinea pig is black, how can you determine if the genotype is BB or Bb? • TEST CROSS: a cross between the individual that shows dominant phenotype and an individual with _______________ phenotype • Examining offspring allows you to determine the genotype of the dominant individual

30. Homozygous recessive Homozygous recessive b b b b B B Bb Bb Bb Bb b B bb Bb bb Bb Punnett Squares of Test Crosses Two phenotypes All dominant phenotypes

31. Beyond Dominant and Recessive Alleles • Genetics is more complicated • Some alleles are neither dominant nor recessive • Other inheritance patterns: • ________________________ • ________________________

32. Incomplete Dominance Homozygous parent (RR) Homozygous Parent (rr) X • When one allele is not completely dominant; recessive allele is not totally masked • Heterozygous phenotype is in between the two homozygous phenotypes • (ex) Red snapdragon flowers (RR) X snapdragon white (rr) flowers  pink hybrid flowers (Rr) All F1 are heterozygous X F2 shows three phenotypes in 1:2:1 ratio

33. Incomplete Dominance homozygous parent homozygous parent X All F1 offspring heterozygous for flower color. Cross two of the F1 plants and the F2 offspring will show three phenotypes in a 1:2:1 ratio:

34. CODOMINANCE • Both alleles contribute to the phenotype • Heterozygous genotype expresses _________________________________ • (ex) Feather colors in chickens: white X black feathers  speckled chicken • (ex) Horse coats: red X white roan coat

35. Codominance: ABO Blood Types 3 different alleles: IA, IB, and i. • IA and IB alleles produces molecules called _______________ on the surface of RBC’s • IA produces A antigens • IB produces B antigens • IA and IB are CODOMINANT  produce both A & B antigens = TYPE ______ BLOOD • iis recessive  if ii, then no antigens are made = TYPE _________ BLOOD

36. Do You Know Your Blood type? Knowing a person’s blood type is critical because using the wrong type of blood during a transfusion can be fatal! Antigen on RBC Safe Transfusions Phenotype (Blood Type) Genotype From To What are the possible genotypes for a person with TYPE A blood? A Type AB person can receive blood from what type of donor? Type O people are often referred to as UNIVERSAL DONORS. Why?