Who is Gregor Mendel?

1. Who is Gregor Mendel? Introduction to Mendelian genetics

2. TRUE OR FALSE? • Girls inherit more traits from their mother than their father • You have inherited traits that are not apparent • Color blindness is more common in males than females • Identical twins are ALWAYS the same sex • A person can transmit genetic traits to their offspring which they themselves DO NOT show • The father determines the sex of a child • The total number of male births exceeds female births each year • Acquired characteristics, like mathematical skills, can be inherited • Fraternal twins are more closely relates to each other than to other siblings

3. Answers • False • True • True • True • True • True • True • False • False

4. Genetics • The field of Biology devoted to understanding how characteristics are passed from parents to offspring

5. Gregor Mendel • In the 19thcentury, Mendel studied heredity-which is the transmission of characteristics from parent to offspring • Mendel is most famous for studying pea plants • He studied what he called “factors” in pea plants • Factors would be things like tall or short (height), or yellow or green (pod color)

6. Some of Mendel’s Factors

7. Gregor Mendel • First, Mendel grew true-breeding plants • According to Mendel, true-breeding plants are plants that will always produce offspring with the same traits • So a true-bred pea plant with purple flowers will only produce plants with purple flowers because it only has the “factors” for purple (not white).

8. Gregor Mendel: P generation • Mendel bred two opposite true-breeding plants • For example, he bred a true-breeding purple flower pea plant and a true-breeding white flower pea plant • He called this his P generation – parent generation

9. Gregor Mendel:F1 generation • All of the offspring of the P generation (which he called the F1 generation) turned out purple • Mendel called purple flower color the dominant factor • He hypothesized that when the dominant factor was present, the recessive factor(white color) did not show.

10. Gregor Mendel:F2 generation • Next, Mendel crossed the offspring from the F1 generation (he called this the F2 generation) • –He observed that about 75% of the flowers were purple and about 25% were white • –This is equal to about a 3:1 ratio

11. Mendel P Generation(true-breeding parents) Purple flowers White flowers F1 Generation(hybrids) All plants had purple flowers F2 Generation

12. Mendel’s Real Results

13. Mendel’s Laws • Keep in mind that Mendel knew nothing of Punnett squares, genes, alleles, or even DNA!!! • All he could do was observe phenotypes and record ratios and other statistics • He came up with 2 important laws as a result of his observations.

14. Mendel’s Laws:Law of Segregation • Mendel concluded that each plant gets two factors (alleles) for a characteristic and when the plant reproduces, these two factors separate or segregate. So… • Each gamete (sex cell) gives one factor (allele) AND therefore… • Each offspring gets one factor from each parent

15. Law of Segregation:Punnett Squares Alleles separate Alleles separate

16. Mendel’s Laws: Law of Independent Assortment • Mendel did experiments using more than one trait (like height and seed color) • He noticed that one trait did not influence the inheritance of another trait • In other words, different factors separate independently of each other during the formation of gametes

17. Mendel’s Laws: Law of Independent Assortment • Examples: • Pea plants can be short or tall • Their seeds can be green or yellow • Short plants can have green or yellow seeds • Tall plants can have green or yellow seeds • So the inheritance of one does not affect the inheritance of the other. • Mendel noticed this with all the traits he studied

18. Independent Assortment

19. Mendel’s Laws • Independent Assortment is not always true- • If different genes are located on the same chromosome, then they will most likely be inherited together • These are called Linked Genes

20. What were Mendel’s factors in reality? • We call these alleles today • –Alleles are alternative forms of a gene • Alleles for flower color were purple and white • The characteristics (like height) are caused by genes on DNA • Genes are segments of DNA that code for one protein • Each gene has 2 alleles, or versions (1 from mom and one from dad)

21. What were Mendel’s factors in reality? • The reason alleles come in pairs is because chromosomes come in pairs (homologous pairs)!! • One allele on each chromosome! • WHAT A COINCIDENCE!!!

22. The Genetics of Mendel’s Experiments • Some Vocab • Dominant trait-masks the recessive • Shown with capital letters • Recessive trait-only shows if dominant is not present • Shown with lower case letters • Phenotype-physical appearance • For example purple, wrinkled, tall, etc

23. The Genetics of Mendel’s Experiments • Some Vocab • Genotype-genetic makeup • This is usually abbreviated with letters like Gg, FF, or hh • Genotypes for a trait are usually2 letters because you get 2 alleles (1 from mom and 1 from dad) • Homozygous-two of the same alleles (like HH or hh) • Heterozygous-two different alleles (like Hh)

24. The Genetics of Mendel’s Experiments • Mendel’s P generation had the genotypes FF (for purple) and ff (for white) • True breeding is also homozygous • FF is homozygous dominant • ff is homozygous recessive

25. The Genetics of Mendel’s Experiments • We can show the results Mendel observed using a Punnett Square: • A Punnett Square shows possible genetic combinations in the zygotes • Mendel crossed his true breeding purple and white flower pea plants • We write this as FF x ff • LET’S DO THIS ON THE BOARD

27. The Genetics of Mendel’s Experiments • What Mendel did not know: • All of F1 pea plant flowers heterozygous (two different alleles), or Ff • That is why they were all purple • Remember dominant alleles mask recessive alleles • So with one purple allele present and one white, only purple would show as it is dominant

28. F2 generation • LET’S EXAMINE EACH RATIO FOR EACH CROSS: • F2 Generation • What genotypes do you start with? • How are they crossed? • What are your results? • What is the genotypic ratio (genes)? • What is the phenotypic ratio of purple (F) to white (f)?

29. Punnett Square Examples • Let’s do a Punnett square for BB x Bb • B= black fur in bunnies • b= white fur in bunnies • Black fur is dominant • What is the genotypic ratio? • What is the phenotypic ratio? • What are the chances for a white bunny?

30. Punnett Square Examples • Let’s look at a heterozygous cross • Bb x Bb • What is the genotypic ratio? • What is the phenotypic ratio? • What are the chances for a white or black bunny?

31. Predicting the Results of Heredity • What do these ratios and percents mean? • If we flip a coin, there is a 50% chance that it will land on heads. But it is still possible to get 5 tails in a row (although it is highly UNLIKELY!) • The more times you flip it, the more likely your results will be 50:50 • If Bb and Bb bunnies mate, there is a 1:4 chance the offspring will be white (this does NOT mean that they will or will not have white bunnies) • If they have LOTS of children, about 25% of them will be white

32. REMEMBER… • Homozygous dominant means 2 BIG letters • Heterozygous means one big one little • Homozygous recessive means 2 little letters • If an organism shows the dominant trait, then the can be either heterozygous OR homozygous dominant

33. Test Cross • When genotypes are not known, a test cross can be performed to figure it out • The organism with an unknown genotype is crossed with a homozygous recessive individual. • Test crosses are often used in breeding (like dog breeding) to determine is organisms are really “pure bred” (homozygous) for desired characteristics

34. Test Cross • Problem: • Let’s say you want to breed black bunnies and you do not want any white bunnies • What would be the only parents’ genotypes to produce black bunnies? • BB x BB • There are 2 ways to know for sure which black bunnies are homozygous and which are heterozygous: expensive genetic testing, or test crosses

35. Test Cross • Solution: • We take some black bunnies and mate them with white bunnies (homozygous recessive) • Let’s look at the Punnett Square results to see the possible results • Remember, black bunnies can be either BB or Bb

36. Test Cross – Punnett Squares(try each cross) • If a BB is crossed with bb, no white bunnies are produced • If a Bb is crossed with bb, then white bunnies may be produced • If a test cross produces white bunnies, we know the unknown genotype is Bb; if not the genotype is BB • The cross would be performed multiple times to be sure of the results

38. Predicting Dihybrid Crosses • When 2 traits are being looked at… • Let’s do a cross between two heterozygous tall, heterozygous purple flowered pea plants • So, TtFfxTtFf • For each plant, we now look at genotype for color and height

39. Predicting Dihybrid Crosses • Instead of 2 possible gametes, there will be 4 • So, the Punnett Square will be 4 x 4 • Phenotypic Ratios • Tall, purple : tall, white : short, purple : short, white • Keep same letters together, capitals 1st • You will not be asked for genotypic ratios for dihybrid crosses • What are the phenotypic ratios? • LET’S DO IT ON THE BOARD

41. Complex Inheritance • Mendel observed monogenic traits and no linked genes…It’s not usually that simple….

42. Other Types of Inheritance • Incomplete Dominance • The phenotype of the heterozygote is intermediate between phenotypes of the dominant and recessive traits • Example: when a homozygous red carnation is crossed with a homozygous white carnations, then pink carnations are produced • We usually don’t use lower case letters in this type of inheritance because nothing is really dominant

43. Incomplete Dominance • RR = Red • RW= pink • WW= white Let’s look at the cross on the board

44. Other Types of Inheritance • Codominance • Occurs when both alleles for a trait are expressed in heterozygous offspring • Codominant alleles are often symbolized with different letters

45. Codominance • BB = Brown • BW= Roan • WW= White • Notice both brown and white are present in the heterozygous genotype

46. Codominance • LET’S EXAMINE THE PUNNETT SQUARE ON THE BOARD • Roan x Roan • BW x BW • What are the ratios for each phenotype?

47. Other Types of Inheritance • Multiple Alleles: • Genes with 3 or more alleles (or variations) • Human blood type shows codominance and it has multiple alleles-A, B, and O

48. Blood Type • Human blood types have 3 alleles A, B, and O. • Each person still only gets 2 alleles, but there are 3 possibilities • O is recessive to A and B, • A and B are codominant: • Genotype AO or AA = A blood • Genotype BO or BB = B blood • Genotype OO = O blood • Genotype AB = AB blood (both alleles expressed)

49. Blood Type

50. TerminologyGenotype • Heterozygous B BO • Heterozygous A AO • Homozygous recessive OO • Homozygous A AA • Homozygous B BB • AB(technically heterozygous) AB