Genetics & The Work of Mendel

1. Genetics&The Work of Mendel

2. Gregor Mendel • The Father of Genetics • Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas • Genetics is the branch of biology that studies heredity • Genetics explains why you have inherited certain traits from your parents • Mendel carried out important studies of heredity – the passing on of characteristics from parents to offspring • Characteristics that are inherited are called traits

3. Why Peas? • Garden peas reproduce sexually • Peas produce male and female sex cells (gametes) • Fertilization is when the male and female gametes unite. • The result is a zygote (fertilized cell) that will eventually develop into a seed

4. Mendel’s Work Pollen transferred from white flower to stigma of purple flower P • Bred pea plants • cross-pollinate true breeding parents (P) • P = parental • raised seed & then observed traits (F1) • F = filial • allowed offspring to self-pollinate& observed next generation (F2) anthers removed all purple flowers result F1 self-pollinate F2

5. Mendel collected data for 7 pea traits

6. true-breeding purple-flower peas true-breeding white-flower peas 100% purple-flower peas F1 generation (hybrids) 100% self-pollinate 75% purple-flower peas 25% white-flower peas 3:1 F2 generation Looking closer at Mendel’s work X P

7. What did Mendel’s Findings Mean? • Traits come in alternative versions • purple vs. white flower color • Purple and white are alleles • Different versions of the same gene purple-flower allele & white-flower allele are two DNA variations at flower-color locus different versions of a gene at the same location on homologous chromosomes

8. Traits are inherited as discrete units • For each characteristic, an organism inherits 2 alleles, 1 from each parent • diploid organism • inherits 2 sets of chromosomes, 1 from each parent What are theadvantages ofbeing diploid?

9. What did Mendel’s findings mean? • Some traits mask others • purple & white flower colors are separate traits that do not blend • purple x white ≠ light purple • purplemaskedwhite • dominant allele • functional protein • affects characteristic • masks other alleles • recessive allele • no noticeable effect • allele makes a malfunctioning protein I’ll speak for both of us! allele producingfunctional protein mutant allele malfunctioningprotein homologouschromosomes

10. X P purple white F1 all purple Genotype vs. phenotype • Difference between how an organism “looks” & its genetics • phenotype • description of an organism’s trait • genotype • description of an organism’s genetic makeup Explain Mendel’s results using …dominant&recessive …phenotype&genotype

11. ___ ___ x X P purple white F1 all purple Making crosses • Can represent alleles as letters • flower color alleles  P or p • true-breeding purple-flower peas  PP • true-breeding white-flower peas  pp ___

12. true-breeding purple-flower peas true-breeding white-flower peas 100% purple-flower peas F1 generation (hybrids) 100% 75% purple-flower peas 25% white-flower peas Looking closer at Mendel’s work phenotype X P ___ ___ genotype ___ ___ ___ ___ self-pollinate 3:1 F2 generation ? ? ? ?

13. PP ___ male / sperm Pp ___ ___ Pp female / eggs pp ___ ___ Punnett squares Aaaaah, phenotype & genotypecan have different ratios F1 generation (hybrids) Pp x Pp % genotype % phenotype ____ ___

14. Genotypes • Homozygous = same alleles = PP, pp • Heterozygous = different alleles = Pp homozygousdominant heterozygous homozygousrecessive

15. purple PP homozygous dominant purple Pp heterozygous How do you determine the genotype of an individual withwith a dominant phenotype? Phenotype vs. genotype • 2 organisms can have the same phenotype but have different genotypes Can’t tellby lookin’at ya!

16. x Test cross • Breed the dominant phenotype —the unknown genotype — with a homozygous recessive (pp) to determine the identity of the unknown allele How does that work? is itPP or Pp? pp

17. P P P p PP Pp pp p p Law of Segregation • Law of segregation • each allele for a trait is packaged into a separate gamete • Organisms receive 1 allele from each parent

18. Monohybrid cross • Some of Mendel’s experiments followed the inheritance of single characters • flower color • seed color • monohybrid crosses (1 trait)

19. Dihybrid cross • Other of Mendel’s experiments followed the inheritance of 2 different characters • seed color andseed shape • dihybrid crosses Mendelwas working outmany of the genetic rules!

20. F1 generation (hybrids) yellow, round peas 100% self-pollinate F2 generation Dihybrid cross P true-breeding yellow, round peas true-breeding green, wrinkled peas x _____ _____ Y = yellow R = round y = green r = wrinkled _____ 9:3:3:1 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas

21. YR YR yR Yr yr yr YyRr What’s going on here? • If genes are on different chromosomes… • how do they assort in the gametes? • together or independently? Is it this? Or this? YyRr Which systemexplains the data?

22. 9/16 yellow round YyRr YyRr 3/16 green round YR YR yr YR yR Yr yr Yr 3/16 yellow wrinkled yR 1/16 green wrinkled yr Dihybrid cross or YyRr x YyRr YR Yr yR yr

23. yellow green round wrinkled Can you thinkof an exceptionto this? Mendel’s 2nd law of heredity • Law of independent assortment • different loci (genes) separate into gametes independently • non-homologous chromosomes align independently • classes of gametes produced in equal amounts • YR = Yr = yR = yr • only true for genes on separate chromosomes or on same chromosome but so far apart that crossing over happens frequently YyRr Yr Yr yR yR YR YR yr yr 1 : 1 : 1 : 1

24. Review: Mendel’s laws of heredity • Law of segregation • monohybrid cross • single trait • each allele segregates into separate gametes • Law of independent assortment • dihybrid (or more) cross • 2 or more traits • genes on separate chromosomes assort into gametes independently

25. Mendel chose peas wisely • Pea plants are good for genetic research • available in many varieties with distinct heritable features with different variations • flower color, seed color, seed shape, etc. • Mendel had strict control over which plants mated with which • each pea plant has male & female structures • pea plants can self-fertilize • Mendel could also cross-pollinate plants: moving pollen from one plant to another

26. Mendel chose peas luckily • Pea plants are good for genetic research • relatively simple genetically • most characters are controlled by a single gene with each gene having only 2 alleles, • one completely dominant over the other

27. Any Questions??