1. Mendelian Genetics Hopefully a Review

2. Gregor Mendel German/Austrian monk in the mid 1800s Father of genetics, heredity  Mendel's Laws Tested the properties of inheritance using peas

3. Heredity Vocabulary A character is a heritable feature, i.e. eye color A character is a heritable feature, i.e. eye color A gene codes for a character A gene codes for a character A trait is a specific variant, i.e. brown eyes A trait is a specific variant, i.e. brown eyes An allele codes for a specific trait An allele codes for a specific trait P Generation (original parent generation) P Generation (original parent generation) F1 – first set of offspring F1 – first set of offspring F2 – second set of offspring (produced by F1 generation) F2 – second set of offspring (produced by F1 generation)

4. Either-Or Traits Mendel studied either-or traits, such as flower color  Flowers were either purple or white Continuums (i.e. height) are usually caused by multiple genes

5. Mendel's Study Mendel Crossed White and Purple flowers Mendel Crossed White and Purple flowers All of the F1 generation were purple (not an intermediate) All of the F1 generation were purple (not an intermediate) F2 generation was 3/4 th purple, 1/4 th white F2 generation was 3/4 th purple, 1/4 th white

6. Mendel's Reasoning The heritable factor for white flowers was present in the F1 generation, but not expressed The heritable factor for purple flowers must dominate the heritable factor for white flowers

7. The Scientific Process Mendel performed nearly a thousand trials on flower color Mendel performed nearly a thousand trials on flower color Also observed the same patterns in 6 other characters Also observed the same patterns in 6 other characters Found similar results Found similar results

8. Mendel's Hypotheses 1) Different versions of genes (alleles) account for variations in inherited characters 2) For each character, an organism inherits one allele from its mother, one from its father a) (Mendel made this assumption with no knowledge of chromosomes!) 3) If the two alleles are different one will be dominant and fully expressed, while the other will have no effect on the individual's appearance

9. Alleles Alleles are the specific genes coding for a particular trait Alleles are the specific genes coding for a particular trait

10. Mendel's Hypotheses con. 4) The two alleles for each character separate when gametes are created (Mendel's law of segregation) Mendel made this claim before chromosomes were discovered and long before meiosis/mitosis was understood Mendel made this claim before chromosomes were discovered and long before meiosis/mitosis was understood But he was mostly right, we do inherit one set of alleles from each parent But he was mostly right, we do inherit one set of alleles from each parent

12. Dominant and Recessive Features Dominant Exhibited if either of a person’s genes are the dominant allele Exhibited if either of a person’s genes are the dominant allele Individuals can have 1 or 2 dominant alleles, in most cases it doesn’t matter Individuals can have 1 or 2 dominant alleles, in most cases it doesn’t matter Recessive Exhibited if both of a person’s genes are the recessive allele Exhibited if both of a person’s genes are the recessive allele A recessive trait can only be expressed with 2 recessive (0 dominant) alleles A recessive trait can only be expressed with 2 recessive (0 dominant) alleles

13. Punnett Squares Let B code for the allele for Purple flowers and b code for the allele for white flowers Let B code for the allele for Purple flowers and b code for the allele for white flowers The original purple flowers were all BB (both alleles were the same) The original purple flowers were all BB (both alleles were the same) The original white flowers MUST HAVE BEEN bb (the only way they could be white) The original white flowers MUST HAVE BEEN bb (the only way they could be white)

14. The F1 Cross

15. The F2 Generation Punnet Square

16. Phenotype vs. Genotype The phenotype of an organism is its appearance for that character The phenotype of an organism is its appearance for that character The genotype is the genetic make up The genotype is the genetic make up Bb or BBbb Bb or BBbb

17. Testcross We can determine the genotype of an organism by crossing (mating) it with an individual with recessive alleles If the offspring are a mix of phenotypes, then the organism was heterozygous If the offspring all exhibit the dominant pattern, then the organism was homozygous dominant

18. Dihybrid Crosses What if we cross individuals differing in 2 characters? Will the dominant alleles stick together and the recessive alleles stick together?

19. NO!!!! Alleles Sort Independently Each allele is inherited independently (unless they are on the same chromosome) Each allele is inherited independently (unless they are on the same chromosome) RrYy x RrYy leads to 9:3:3:1 pattern RrYy x RrYy leads to 9:3:3:1 pattern

20. Probability/ The Multiplication Rule The odds of 2 events both happening = the odds of one times the odds of the other The odds of 2 events both happening = the odds of one times the odds of the other I.e. the odds of pulling a red jack out of a deck = 1/2 * 1/13 = 1/26 (or 2/52) I.e. the odds of pulling a red jack out of a deck = 1/2 * 1/13 = 1/26 (or 2/52) The odds of rolling 3 6’s in a row = 1/6 * 1/6 * 1/6 = 1/216 The odds of rolling 3 6’s in a row = 1/6 * 1/6 * 1/6 = 1/216

21. The Multiplication Rule Assume heterozygous parents Assume heterozygous parents Probability of both alleles ending up recessive = probability of receiving allele from mother * probability of receiving allele from father = ½ * ½ = ¼ Probability of both alleles ending up recessive = probability of receiving allele from mother * probability of receiving allele from father = ½ * ½ = ¼

22. Multiplication Rule Assume parents are YyRr Assume parents are YyRr The odds of giving a recessive trait are ½ for each character The odds of giving a recessive trait are ½ for each character The odds of a parent giving 2 recessive alleles (yr) is ¼ (1/2 * ½) The odds of a parent giving 2 recessive alleles (yr) is ¼ (1/2 * ½) Thus the odds of offspring ending up with 2 recessive traits from both parents is ¼ * ¼ = 1/16 Thus the odds of offspring ending up with 2 recessive traits from both parents is ¼ * ¼ = 1/16

23. The Addition Rule The odds of either of 2 events occurring is found by adding them The odds of either of 2 events occurring is found by adding them I.e. the odds of rolling a 1 or a 6 = 1/6 + 1/6 = 1/3 I.e. the odds of rolling a 1 or a 6 = 1/6 + 1/6 = 1/3 The odds of pulling an Ace or a King = 1/13 + 1/13 = 2/13 The odds of pulling an Ace or a King = 1/13 + 1/13 = 2/13

24. The Rule of Addition There are two possibilities to end up heterozygous with heterozygous parents There are two possibilities to end up heterozygous with heterozygous parents To find the probability of ending up heterozygous you add the individual odds To find the probability of ending up heterozygous you add the individual odds ¼ + ¼ = ½

25. The other method Make a dihybrid or trihybrid cross Make a dihybrid or trihybrid cross List every possible combination of alleles each parent could give List every possible combination of alleles each parent could give So for 2 MmNn individuals, you would have: So for 2 MmNn individuals, you would have: MNMnmNmn MNMMNNMmNnMmNNMmNn MnMMNnMMnnMmNnMmnn mNMmNNMmNnmmNNmmNn mnMmNnMmnnmmNnmmnn

26. Calculating the Probability Imagine a tri-hybrid cross, with two parents who are MmNnOo. What are the odds of ending up recessive in all 3 characters? Imagine a tri-hybrid cross, with two parents who are MmNnOo. What are the odds of ending up recessive in all 3 characters? Chances of ending up recessive for each character individually = ¼ Chances of ending up recessive for each character individually = ¼ so the odds of ending up recessive in 3 is ¼ * ¼ * ¼ = 1/64 so the odds of ending up recessive in 3 is ¼ * ¼ * ¼ = 1/64

27. As a Group Calculate…(assume MmNnOo parents) 1. What are the odds of ending up MmNnOo 2. MMNNoo 3. MmNNOo 4. Expressing the dominant trait for M and N but recessive trait for o 5. Dominant in exactly 2 of the 3 traits

28. Quick Practice A mother is AaBBDdee. What possible alleles can her eggs have? A mother is AaBBDdee. What possible alleles can her eggs have? Two AaBb individuals mate. What are the odds their offspring are homozygous dominant in both? Two AaBb individuals mate. What are the odds their offspring are homozygous dominant in both? An AAbbDD man mates with a woman heterozygous in all 3 traits. What are the odds an offspring has the same genotype as one of their parents? An AAbbDD man mates with a woman heterozygous in all 3 traits. What are the odds an offspring has the same genotype as one of their parents? An AABBDDEEFFGG man mates with an aabbddeeffgg woman. What % of their offspring will be heterozygous? An AABBDDEEFFGG man mates with an aabbddeeffgg woman. What % of their offspring will be heterozygous?

29. Review Some alleles dominate others We inherit one allele from each parent Alleles are inherited separately Probability is observed in the long run

30. The Relationship Between Genotype and Phenotype is Rarely So Simple! Mendel was lucky, he chose characters controlled by 1 gene, where 1 trait is completely dominant Mendel was lucky, he chose characters controlled by 1 gene, where 1 trait is completely dominant Things are not always so simple Things are not always so simple Doesn't mean Mendel is wrong! Doesn't mean Mendel is wrong!

31. Incomplete Dominance For some characters, heterozygous individuals exhibit phenotypes that are a mix of the 2 alleles i.e. red and white flowers can produce pink flowers Pink flowers produce red, white and pink offspring Not blending!

32. Codominance/ Multiple Alleles The two alleles can both be expressed at the same time i.e. Blood Types A and B are dominant to O (3 alleles) A and B are codominant

33. Blood Types AA or AO individuals produce A antigens BB or BO individuals produce B antigens AB produce both OO produce none Individuals cannot receive blood with A or B antigens unless their blood produces them

34. 3 Important Points About Dominance 1) Ranges from complete dominance to incomplete dominance to codominance 2) The dominant allele does not suppress or interact with the other allele. The recessive allele simply isn't expressed by the cells 3) A trait being dominant does not necessarily mean it is more common in the population

35. Dominant but Rare Traits 6 fingers 6 fingers Dwarfism Dwarfism Widow’s Peak Widow’s Peak Dimples Dimples Cleft chin Cleft chin Ear wiggling Ear wiggling Hair on middle of fingers Hair on middle of fingers

36. Pedigrees Obviously in humans we can't choose who breeds with whom Obviously in humans we can't choose who breeds with whom Mendelian patterns are observed using pedigrees Mendelian patterns are observed using pedigrees Geneticists collect information about a specific trait from a family Geneticists collect information about a specific trait from a family

37. How to Read Pedigree Charts Squares represent males, circles represent females A line represents mating Shading represents that the trait is present

38. How Can You Spot a Recessive Trait? If it appears in offspring but neither parent had it If it appears in offspring but neither parent had it Both parents must have been carriers Both parents must have been carriers ff Ff ff Ff FF or Ff Ff

39. How Can you Spot a dominant trait? If two parents have the trait, but the offspring does not! If two parents have the trait, but the offspring does not! The parents must be heterozygous and have a recessive offspring The parents must be heterozygous and have a recessive offspring Ff ff Ff