Inheritance Overview

1. Inheritance Overview

2. 23.1 Mendel’s laws • Gregor Mendel • An Austrian monk, who combined his farmer’s skills with his training in mathematics and developed certain laws of heredity in 1860 after doing crosses between garden pea plants. • Published a paper stating that parents pass discrete heritable factors on to their offspring • Factors retain individuality generation after generation • Identified that each trait is inherited by a pair of factors, one from each parent • One form of a factor may be dominant over an alternative form • Reasoned that each egg and sperm must contain only 1 copy of a factor for each trait

3. Mendel’s laws cont’d. • His research and his findings led to develop what we call Mendel’s law of segregation; • Each individual has two factors (genes) for each trait • The factors segregate (separate) during the formation of gametes • Each gamete contains only one factor from each pair of factors • Fertilization gives each new individual 2 factors for each trait

4. Mendel’s laws cont’d. Mendel’s law of segregation 1. Each individual has two factors (genes) for each trait. We now know that these factors are what we call genes and that genes are sections of chromosomes. We have a pair of each chromosome, known as homologous pairs whichhave genes controlling the same traits located at the same point, or locus, on each member of the pair • Information contained within the homologous genes is not necessarily the same (ex: widow’s peak vs. straight hairline) • Alternative forms of a gene for a specific trait are called alleles

5. Mendel’s laws cont’d. 2. The factors segregate (separate) during the formation of gametes. This is due to Independent Assortment of Homologous Chromosomes during Meiosis.

6. Mendel’s laws cont’d. 3. Each gamete contains only one factor from each pair of factors. Gametes are haploid, which means they only have 1 chromosome of each pair, therefore each gamete has only one allele of the pair of alleles for a trait

7. Mendel’s laws cont’d. • 4. Fertilization gives each new individual 2 factors for each trait. • 2 Haploid Gametes combine to form a Diploid Zygote. Diploid means that it has a pair of each chromosome and therefore a pair of alleles for a given trait.

8. Gene locus

9. Mendel’s laws cont’d. Inheritance of a single trait • In simple dominance, one form of the allele is dominant over the other form which is recessive. • Capitol letter- represents the dominant allele • Small letter- represents the recessive allele • Dominant-a certain trait will result if the individual has at least 1 dominant allele • Recessive- for a recessive trait to result the individual must have 2 copies of the recessive allele

10. The inheritance of a single trait cont’d. • Phenotype- physical appearance of the individual with regard to a trait. • Genotype- genetic composition of an individual with regard to a specific trait • Homozygous - 2 copies of the same allele for a specific trait • Heterozygous – 1 of each of the 2 copies of the allele for that trait • 2 copies of the dominant allele- homozygous dominant • 1 copy of the dominant allele and 1 of the recessive- heterozygous • 2 copies of the recessive allele- homozygous recessive

11. Mendel’s laws cont’d. • The inheritance of a single trait cont’d. Phenotype vs. Genotype • Homozygous dominant individual and heterozygous individual. These 2 individuals will have the same phenotype but different gentoypes. • Homozygous recessive individual will have a different phenotype than the other 2 individuals. • Example- inheritance of a widow’s peak vs. a straight hairline in humans • Alternative forms of alleles for hairline shape • Widow’s peak is dominant to straight • W=allele for widow’s peak • w= allele for straight hairline

12. Widow’s peak

13. Mendel’s laws cont’d. • Inheritance of a single trait cont’d. • Gamete formation • During meiosis, homologous chromosomes separate so there is only 1 member of each pair in a gamete • There is one allele for each trait, such as hairline, in each gamete • No two letters in a gamete can be the same letter of the alphabet • If genotype is Ww, then gametes from this individual will contain either a W or a w • If the genotype is WwLl (looking at 2 traits), gametes can contain any of the following combinations • WL, Wl, wL, or wl

14. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW • WWSs • Tt • Ttgg • AaBb • For each of the following, state whether the genotype or a gamete is represented • D • Ll • Pw • LlGg

15. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs • Tt • Ttgg • AaBb • For each of the following, state whether the genotype or a gamete is represented • D • Ll • Pw • LlGg

16. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs Gametes – WS or Ws • Tt • Ttgg • AaBb • For each of the following, state whether the genotype or a gamete is represented • D • Ll • Pw • LlGg

17. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs Gametes – WS or Ws • Tt Gametes – T or t • Ttgg • AaBb • For each of the following, state whether the genotype or a gamete is represented • D • Ll • Pw • LlGg

18. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs Gametes – WS or Ws • Tt Gametes – T or t • Ttgg Gametes – Tg or tg • AaBb • For each of the following, state whether the genotype or a gamete is represented • D • Ll • Pw • LlGg

19. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs Gametes – WS or Ws • Tt Gametes – T or t • Ttgg Gametes – Tg or tg • AaBb Gametes – AB or aB or Ab or ab • For each of the following, state whether the genotype or a gamete is represented • D • Ll • Pw • LlGg

20. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs Gametes – WS or Ws • Tt Gametes – T or t • Ttgg Gametes – Tg or tg • AaBb Gametes – AB or aB or Ab or ab • For each of the following, state whether the genotype or a gamete is represented • D Gamete (has one allele for a trait) • Ll • Pw • LlGg

21. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs Gametes – WS or Ws • Tt Gametes – T or t • Ttgg Gametes – Tg or tg • AaBb Gametes – AB or aB or Ab or ab • For each of the following, state whether the genotype or a gamete is represented • D Gamete (has one allele for a trait) • Ll Genotype (has 2 alleles for a trait) • Pw • LlGg

22. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs Gametes – WS or Ws • Tt Gametes – T or t • Ttgg Gametes – Tg or tg • AaBb Gametes – AB or aB or Ab or ab • For each of the following, state whether the genotype or a gamete is represented • D Gamete (has one allele for a trait) • Ll Genotype (has 2 alleles for a trait) • Pw Gamete (has one allele for each of 2 traits) • LlGg

23. Mendel’s laws cont’d. • Practice problems • For each of the following genotypes, give all possible gametes • WW Gametes – All W • WWSs Gametes – WS or Ws • Tt Gametes – T or t • Ttgg Gametes – Tg or tg • AaBb Gametes – AB or aB or Ab or ab • For each of the following, state whether the genotype or a gamete is represented • D Gamete (has one allele for a trait) • Ll Genotype (has 2 alleles for a trait) • Pw Gamete (has one allele for each of 2 traits) • LlGg Genotype (has 2 alleles for each of 2 traits)

24. Genotype related to phenotype

25. Mendel’s laws cont’d. • One trait crosses-monohybrid cross • In one-trait crosses, only one trait such as type of hairline is being considered. • Let’s consider a specific cross • If a homozygous woman with a widow’s peak reproduces with a man with a straight hairline, what kind of hairline will their children have? • Use W= widow’s peak, w=straight hairline • figure out the genotype of each parent: • Woman has a widow’s peak and we are told she is homozygous so she is WW • Man has a straight hairline so he must be ww • Determine their gametes: her eggs will all have W and his sperm will all have w • Put together all possible combinations: all offspring will receive a W from her and a w from him so all will have Ww

26. Mendel’s laws cont’d. • One-trait cross cont’d. • In this example there was only 1 combination of eggs and sperm possible. The children are all monohybrids, they are heterozygous for one pair of alleles. • What if the parents were each Monohybrids (Ww)? • Then sperm could have either W or w, and eggs also could have W or w • One way to figure out all of the possible combinations of eggs and sperm that can occur is to use a Punnett square • This is illustrated on the following slide

28. Mendel’s laws cont’d. • One-trait cross cont’d. • After the genotypes and phenotypes of offspring are determined, we can determine the ratios • In our previous example, in the Punnett square we had the following offspring: WW, Ww, Ww, and ww • The genotypic ratio is 1 WW:2 Ww:1 ww • The phenotypic ratio is 3 individuals with a widow’s peak to 1 individual with a straight hairline. • When a monohybrid reproduces with a monohybrid (a monohybrid cross) the ratio of expected phenotypes expressed in the offspring is 3 : 1. • Another way to phrase the phenotypic ratio is in terms of probability • This couple has a 75% chance of producing a child with a widow’s peak and a 25% chance of producing a child with a straight hairline • The probability will be the same for each pregnancy between this couple

29. Mendel’s laws cont’d. • One-trait crosses and probability • Product rule of probability • The chance of 2 or more independent events occurring together is the product of their chance of occurring separately • In the cross Ww X Ww, what is the chance of obtaining either a W or a w from a parent? • Chance of W = ½ and the chance of w = ½ • Therefore the probability of having these genotypes is as follows • Chance of WW= ½ X ½ = ¼ • Chance of Ww = ½ X ½ = ¼ • Chance of wW= ½ X ½ = ¼ • Chance of ww = ½ X ½ = ¼

30. Mendel’s laws cont’d. • One-trait crosses and probability cont’d. • Sum rule of probability-the chance of an event that can occur in more than one way occurring a certain way is the sum of the individual chances of it occurring that way. • To calculate the chance of an offspring having a widow’s peak, add the chances of WW, Ww, or wW from the preceding slide ¼ + ¼ + ¼ = ¾ or 75%

31. Mendel’s laws cont’d. • The one-trait test cross • You cannot distinguish between a homozygous dominant individual and a heterozygous individual just by looking because they are phenotypically the same • Breeders of plants and animals may do a test cross to determine the likely genotype of an individual with the dominant phenotype • Cross with a recessive individual which has a known genotype - homozygous recessive. • If there are any offspring produced with the recessive phenotype, then the dominant parent must be heterozygous

32. One-trait testcross When crossed with Recessive all resulting offspring show the dominant trait. Therefore the dominant parent must be Homozygous Dominant

33. One-trait testcross When crossed with Recessive some resulting offspring show the dominant trait and some show the recessive trait. Therefore the dominant parent must be Heterozygous Dominant

34. Mendel’s laws cont’d. • Practice problems Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles? Mother - _____________ Father - _____________

35. Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles? Mother - _____Ff________ Father - ___Ff__________

36. Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles? Mother - _____Ff________ Father - ___Ff__________

37. Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles? Mother - _____Ff________ Father - ___Ff__________

38. Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles? Mother - _____Ff________ Father - ___Ff__________

39. Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles? Mother - _____Ff________ Father - ___Ff__________

40. Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles? Mother - _____Ff________ Father - ___Ff__________

41. Both a man and a woman are heterozygous for freckles. Freckles are dominant over no freckles. What is the chance that their child will have freckles? Mother - _____Ff________ Father - ___Ff__________ 3:1 Ratio Freckles:No Freckles 75% Chance child will have Freckles

42. Both you and your sibling have attached ear lobes, but your parents have unattached lobes. Unattached earlobes (E) are dominant over attached (e). What are the genotypes of your parents? Mother - _____________ Father - _____________

43. Both you and your sibling have attached ear lobes, but your parents have unattached lobes. Unattached earlobes (E) are dominant over attached (e). What are the genotypes of your parents? Mother - _____________ Father - _____________

44. Both you and your sibling have attached ear lobes, but your parents have unattached lobes. Unattached earlobes (E) are dominant over attached (e). What are the genotypes of your parents? Mother - _____________ Unattached Earlobes Father - _____________ Unattached Earlobes

45. Both you and your sibling have attached ear lobes, but your parents have unattached lobes. Unattached earlobes (E) are dominant over attached (e). What are the genotypes of your parents? Mother - _____________ Unattached Earlobes Father - _____________ Unattached Earlobes

46. Both you and your sibling have attached ear lobes, but your parents have unattached lobes. Unattached earlobes (E) are dominant over attached (e). What are the genotypes of your parents? Mother - ____Ee_________ Unattached Earlobes Father - ___Ee__________ Unattached Earlobes Parents had to both be (Ee) Heterozygous Dominant to have a recessive offspring

47. A father has dimples, the mother of his children does not, and all 5 of their children have dimples. Dimples (D) are dominant over no dimples (d). Give the probable genotypes of all persons concerned. Mother - _____________ Father - _____________

48. A father has dimples, the mother of his children does not, and all 5 of their children have dimples. Dimples (D) are dominant over no dimples (d). Give the probable genotypes of all persons concerned. Mother - _____________ Father - _____________

49. A father has dimples, the mother of his children does not, and all 5 of their children have dimples. Dimples (D) are dominant over no dimples (d). Give the probable genotypes of all persons concerned. Mother - _____________ No Dimples Father - _____________ Dimples

50. A father has dimples, the mother of his children does not, and all 5 of their children have dimples. Dimples (D) are dominant over no dimples (d). Give the probable genotypes of all persons concerned. Mother - __dd_________ No Dimples Father - _____________ Dimples