Intro to Genetics and Mendel Honors Biology Ms. Kim

1. Intro to Genetics and Mendel Honors Biology Ms. Kim

2. Transmission (passing down) of Traits How? • One possible explanation of heredity is a “blending” hypothesis • genetic material contributed by two parents mixes

3. Another Hypothesis • An alternative to the blending model is the hypothesis of inheritance (genes) • Parents pass on discrete heritable units (factors) called genes • http://wps.aw.com/bc_campbell_biology_7/29/7523/1925929.cw/nav_and_content/index.html • The Novelty Gene Video

4. Figure 14.1 Gregor Johann Mendel (1843) • Austrian Monk- “Father of Modern Genetics” • Documented a mechanism of inheritance through his experiments with garden peas • The scientific study of heredity is called GENETICS! • Worked with pea plants in his monastery • Correctly believed that heritable factors (genes) retain their individuality from generation to generation • i.e. – marbles (no blending of colors!)

5. Gregor Johann Mendel • Mendel used the scientific method to identify two laws of inheritance • Mendel discovered the basic principles of heredity • By breeding garden peas in carefully planned (CONTROLLED) experiments

6. Mendel’s Experimental Method • Why did Mendel choose pea plants? • available in many varieties of traits • They have seven distinct & observable traits • easy to get • he could strictly control which plants mated with which • Grow quickly • They reproduce quickly & have a short life cycle • They produce many offspring in one cross

7. Mendel’s Experimental Cross Purebred white and purple flowers • All Purple • All White • Both White/Purple Offspring were allowed to self pollinate White flowers reappear in some offspring What did Mendel notice? Did the trait for white flowers disappear in F1 generation?

8. Some genetic vocabulary • Character: a heritable feature, such as flower color • Trait: a variant of a character, such as purple or white flowers

9. Mendel observed the same pattern • In many other pea plant characters

10. Pea Plant Fertilization • Self fertilization : mate with self  produce identical offspring • TRUE or PURE breeds • Cross fertilization : mate with another  can produce different offspring • HYBRIDS • http://wps.aw.com/bc_campbell_biology_7/29/7523/1925929.cw/nav_and_content/index.html • Colored Cotton Video

11. Mendel’s Experiment • Mendel only looked at “either-or” characters • Ex: Purple OR white flowers • Mendel started his experiments with “true-breeding” • Made through self fertilization so plants are “TRUE” for only 1 trait • Known as HOMOZYGOUS for trait

12. What was Mendel’s Procedure? 1. He made 14 “TRUE BREEDS” • 1 for EACH trait he looked at • These are the original parents • Are called the P generation

13. What was Mendel’s Procedure? 2. He used cross fertilization to mate 2 true breeds for same gene • Ex: Purple vs white flower color 3. He collected the offspring (progeny) • The hybrid (mixed) offspring of theP generation • Are called the F1 generation

14. What was Mendel’s Procedure? 4. He crossed (using cross fertilization) male and female from F1 progeny • When F1 individuals are mated together • The F2 generationis produced

15. P Generation (true-breeding parents)  Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation What did Mendel Discover? P  F1  F2 • A 3:1 ratio, purple to white flowers, in the F2 generation Where did the white color go?

17. Genetics Vocab P generation parental generation have offspring called the F1 generation (hybrids) Hybrid (F1) the offspring of two true breeding varieties If F1 generations self-fertilize/cross, their offspring are called the F2 generation Mendel worked with his pea plants until he was sure that all were true-breeding varieties (pure bred)

18. Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers Figure 14.4 What are Mendel’s factors? • Mendel’s “factors” are now called alleles • Alternative version or form of a gene F f

19. Mendel’s Experiments • After studying pea plants, Mendel concluded that: • Traits are passed from one generation to the next through genes. • Each trait is controlled by a different form of a gene called an allele • Some alleles are dominantto others called recessive traits • New question: Have the recessive alleles disappeared or are they still present in the parents?

20. What did Mendel Conclude? • Mendel reasoned that • In the F1 plants, only 1 factor (ex: purple flower) was affecting physical outcome color in hybrids • This factor was dominant and the hidden factor was recessive

21. Recessive is… • Represented by a lowercase letter (it is NOT the letter itself, though) • an allele that does NOT produce a characteristic effect when present with a dominant allele • only expressed when present with another (identical) recessive allele • This is known as the homozygous condition • aa or hh

22. Dominant is… • Represented by a uppercase letter • an allele that produces the same trait whether inherited with a another dominant allele (homozygous) or with a recessive allele (heterozygous) • Aa or AA • The allele that is expressedif present

23. Frequency of Dominant Alleles • Dominant alleles • Not necessarily better, stronger, etc.than recessive alleles • Ex: Polydactyl

24. Mendel’s Experiments • Mendel crossed the first generation and saw that the recessive trait showed up in about 1 of 4 plants. • Conclusion: Law of Segregation! • What is the Law of Segregation?! • Organisms inherit two copies of each gene (one from each parent) • Organisms donate only one copy of each gene in their gametes (sex cells) • Therefore, the two copies of each gene segregate (separate) during gamete formation (meiosis)

25. The Law of Segregation: Mendel’s 1st Law • Each gamete ONLY gets 1 allele

26. More about Alleles… • Each individual has 2 alleles for the same gene • located on homologous chromosomes • Each parent passes 1 allele for each gene to his/her offspring • In sperm or egg • What stage of meiosis are alleles segregated into gametes? • Meiosis Anaphase I

27. a A

28. Mendel’s Observations • Used pea plants to see patterns in the way various traits were inherited • Using his data, he saw that different traits are inherited separately • Example: Green pea color isn’t always inherited with wrinkled pea shape • Green peas can be smooth and round too! • This is called the Law of Independent Assortment!

29. What is the Law of Independent Assortment? • Allele pairs (traits) separate independently of each other during gamete formation (meiosis) • Different traits are inherited separately • Example – peas can be green and wrinkled OR green and round • This explains genetic diversity among organisms

30. Law of Independent Assortment:Mendel’s 2nd Law • Says genes are inherited independently of other genes • Genes are not linked unless on the same chromosome! • Mendel assumed traits occur on different chromosomes! • Occurs during Metaphase I

31. Useful Genetic Vocabulary • Homozygous • A pair of IDENTICAL (same) alleles for that gene • Exhibits true-breeding • aa = homozygous recessive(or just recessive) • HH = homozygous dominant • Heterozygous • Pair of alleles that are different for that gene • Aa or Hh

32. More Genetic Vocabulary • An organism’s genotype • Is its genetic (DNA) makeup • A.k.a.-the allele combination (includes 2 alleles) • An organism’s phenotype • Is its physical outcome of the genotype • Ex: blue eyes or AB blood type

33. Mendelian Genetics…aka-COMPLETE DOMINANCE If an organism is heterozygous (Hh), • The effect of the recessive allele is HIDDEN • Heterozygous and homozygous dominant have SAME phenotype • The 1st allele is “completely dominant” over the 2nd allele

34. Phenotype Genotype Purple PP (homozygous) Pp (heterozygous) 3 pp (homozygous) White Ratio 3:1 Ratio 1:2:1 Figure 14.6 1 Purple 2 Pp (heterozygous) Purple 1 1

35. Why Did Mendel Keep Getting the SAME results? • We can answer this question using a Punnett square • a diagram (box) used to predict probabilities of possible outcomes for offspring that will result from a cross between 2 parents • SHOWS EXPECTED RESULTS (not necessarily actual)

36. Practice PURPLE X WHITE PURPLE PURPLE & WHITE • Which flower color is recessive? • White • Purple • Neither • Both

37. Practice PURPLE X WHITE PURPLE PURPLE & WHITE • Which flower color is recessive? • WHITE • What would the genotype be for the recessive flower? A. PP homozygous dominant B. pp homozygous recessive C. Pp Heterozygous

38. Practice PURPLE X WHITE PURPLE PURPLE & WHITE • Which flower color is recessive? • WHITE • What would the genotype be for the recessive flower? • pp homozygous recessive • Which flower color is dominant? • White • Purple • Neither • Both

39. Practice PURPLE X WHITE PURPLE PURPLE & WHITE • Which flower color is recessive? • WHITE • What would the genotype be for the recessive flower? • pp homozygous recessive • Which flower color is dominant? • PURPLE • What would the genotype be for the dominant flower color? A. PP homozygous dominant B. Pp heterozygous C. pp homozygous recessive D. Both A & B

40. Genetics Vocab (pt 2) • Monohybrid cross cross where parents differ in only one trait (Rr x rr) • Dihybrid cross cross where parents differ in two traits (RrHh x rrHH) • Punnett square – a diagram that shows the gene combinations that mightresult from a genetic cross of two parents