Unit 3: Genetics

1. Unit 3: Genetics

2. 1. Explain the significance of Mendel`s experiments and observations and the laws derived from them. a. Explain the concept of independent events. b. Understand that the probability of an independent event is not altered by the outcomes of previous events.

3. Heredity All organisms pass on their characteristics from generation to generation through INHERITANCE. 2 kinds of characteristics inherited: Species characteristics: each species always passes on their own traits. Individual Characteristics: even though we inherit things equally from both parents, offspring is always different from their parents because we are a combination of both parents (i.e. mother's hair colour, father's build, mother's nose, etc.) Heredity is controlled by a chemical code in our DNA. This genetic code is present in the chromosomes of the gametes (egg and sperm).

4. Environment Even though we inherit traits from our parents, our environment will affect the full potential of what we inherit. Example: Food: people in Canada are bigger and taller than 100 years ago Exercise: stronger, healthier bodies Sunlight: lightens hair, darkens freckles Independent Events Another factor that will affect what we inherit are independent events. An event that takes place that no previous event has an effect on. Example: you broke your finger when you were six and it is now crooked. You will not pass this crooked finger on to any of your offspring, it is an independent event.

5. Probability In genetics, we use a mathematical process called probability. Probability is the chance that an event will occur (i.e. the chance that you will have curly hair or blue eyes). When determining probability, we do not consider items like the environment or independent events.

6. In-Class Discussion How does heredity affect you? What traits have you received that are NOT affected by the environment or independent events? What traits have you received that have been affected by the environment or independent events Instructions: 1. In groups of 2 or 3, discuss the 3 questions above, make a list of traits that have been inherited, and a list of traits that have been affected/altered. 2. Look at the list of traits that your group has made and decide which ones are most common and which ones are not as common....decide what this might have to do with the terms "dominant" and "recessive".

7. List of Traits: Dominant or Recessive:

8. Dominant and Recessive Genes Dominant Gene: determine the expression of the genetic trait in offspring. Dominant gene is given an upper case (capital) letter. Recessive Gene: genes that are overruled by dominant genes. Recessive gene is designated by a lower case letter. Other Examples: To determine some other examples of traits that are dominant or recessive, we will conduct a class survey. http://www.uni.edu/walsh/genetics.html

9. Review... 1. What does the term "heredity" mean? 2. What is the difference between a dominant and a recessive trait? Provide an example of each.

10. 1. Explain the significance of Mendel`s experiments and observations and the laws derived from them. c. Describe Mendel`s experiments and observations. d. Describe the relationship between genotype and phenotype. e. Use the concept of the gene to explain Mendel`s Laws. f. Describe the ideas of dominant and recessive traits with examples. h. Explain the law of segregation.

11. GENETICS GENETICS: the branch of biology that studies the ways in which 
hereditary information is passed on from parents to offspring. GREGOR MENDEL: (1822-1884) first to study heredity (monk). studied pea plants (traits) and came up with some basic principles. Peas: easy to grow, mature quickly, show sharply contrasting traits 
(tall vs. short, yellow vs. green, wrinkled vs. smooth). Easy to cross pollinate for humans. Kept careful records.

12. Mendel and His Experiments Gregor Mendel:  Austrian monk  1822-1884  studied garden peas Mendel studied peas and cross-fertilized them by hand. Peas had specific 
traits that he studied. Crosses:  Round seeds X Wrinkled (parents)   Round Seeds (offspring)  Tall plants X Short plants (parents)   Tall Plants (offspring) Yellow seed coats X Green seed coats (parents)   Yellow seed coats (offspring)

13. Mendel discovered that genes control the traits of a plant. Genes are located 
on chromosomes. Mendel also discovered that some genes are dominant over others 
(recessive). Ex)  round seeds dominant over wrinkled seed  tall plants dominant over short plants  yellow seed coat dominant over green seed coats Dominant Gene: determine the expression of the genetic trait in offspring. Dominant gene is given an upper case (capital) letter. Recessive Gene: genes that are overruled by dominant genes. Recessive gene is designated by a lower case letter. For each trait, an organism gets one gene form the mother and one gene 
from the father.

14. Mendel's Laws of Heredity: 1. Inherited characteristics are controlled by genes. Genes happen in pairs. During fertilization 2 genes come together to form a pair. 2. Principle of Dominance one gene masks the effect of another. The gene for round seed coats masks the effect of the gene for wrinkled seed 
coats. Round is dominant over wrinkled. 3. Law of Segregation: Genes separate during the formation of sex cells. Organisms get one gene from each parent for a particular trait. During the 
formation of gametes (sex cells), alleles (form of a gene) separate randomly 
so that each gamete receives one or the other. The Law of Segregation 
deals with meiosis, which will be talked about later.

15. Genotype: refers to the genes that an organism has for a particular trait. Ex) RR, Rr, rr; a round seed coat can have genotype RR or Rr, a wrinkled seed coat has only one genotype rr. YOU CAN'T TELL THE GENOTYPE BY JUST LOOKING AT AN ORGANISM Phenotype: refers to the observable traits of an organism, the traits that you see, Ex) there are only 2 phenotype for seed coat, wrinkled and smooth. Homozygous: an organism contains 2 genes for one trait that are the same, Ex) RR or rr : the organism is pure for the trait. Heterozygous: an organism contains 2 genes for one trait that are different. Ex) Rr Alleles: two or more alternate forms of a gene. Ex) Dominant Recessive seed coat alleles R (smooth) r (wrinkled)

16. Review.... 1. List and explain one of the new terms learned last day. 2. What was one of Gregor Mendal's laws?

17. 1. Explain the significance of Mendel`s experiments and observations and the laws derived from them. g. Consider the value of the punnett square by creating examples of mono and dihybrid crosses.

18. Monohybrid Cross Mono (one) Hybrid (result from crosses between parents that are genetically not 
alike) Monohybrid Cross: a cross that involved one pair of contrasting genes for 
one trait.

19. Ex) Dealing with the trait of Seed Coat Round seed coat X Wrinkled seed coat (parent) RR rr Crossed Again (F1 generation) Hybrid Offspring X Rr Round Seed Coat Rr (F = filial) rr Rr RR Rr (F2 generation)

20. Punnet Square for Monohybrid Cross Punnet Square: chart used by geneticists to show the possible combinations of alleles in offspring. Wrinkled Parent (homozygous) r r R Round Parent (homozygous) R (F1 generation) all _ Rr, heterozygous

21. Round Parent (heterozygous) r R R Round Parent (heterozygous) r (F2 generation) _ RR homozygous dominant, _ Rr heterozygous and _ rr homozygous (recessive)

22. Monohybrid Cross Genotypic Ratio 1 RR (homozygous dominant) : 2Rr (heterozygous) : 1rr (homozygous recessive) Monohybrid Cross Phenotypic Ratio 3 round : 1 wrinkled 3 with the dominant trait showing : 1 with the recessive trait showing 3/4 or 75% : 1/4 or 25%

23. Lets look at this in more detail. X rr RR (parents) sex cells R R sex cells r r Rr (F1 generation) X Rr sex cells R r (F2 generation) RR Rr Rr rr round wrinkled

24. Examples: 1. Brown eyes (B) are dominant over blue eyes. If a parent homozygous for blue eyes produce offspring. What are the chances that the offspring has brown eyes? blue eyes? Parent A = BB Parent B = bb

25. 2. In plants, tall (T) is dominant over short (t). Two plants, that are tall, are crossed and produce a plant that is short. Determine the genotype of the parents. short plant = tt

26. 3. In guinea pigs, curly hair (C) is dominant over straight hair (c). If two guinea pigs that have curly hair and are straight hair carriers mate, what is the chance they have a straight haired offspring? Genotype of parents =

27. 1. Explain the significance of Mendel`s experiments and observations and the laws derived from them. g. Consider the value of the punnett square by creating examples of mono and dihybrid crosses.

28. Review Question.... 1. Both a hen and a rooster are heterozygous trait carriers. They both have a trait to be black (B) and a trait to be white (b). Black is the dominant colour, what will the phenotypes and genotypes of their offspring be?

29. Dihybrid Cross Di = 2 Hybrid: result from crosses between parents that are genetically not alike. Dihybrid cross: a cross that involves 2 traits.

30. Example of a dihybrid cross: Yellow Round X Green Wrinkled (parent) (gametes YR) yyrr YYRR (gametes yr) Crossed Again (F1 generation) X Yellow Round YyRr YyRr (gametes = YR, Yr, yR, yr) (gametes = YR, Yr, yR, yr) (F2 generation) 1 YYRR, 2 YyRR, 2 YYRr, 4 YyRr, 1 YYRR, 2 yyRr, 1 yyrr, 1 YYrr

31. Punnet Square for Dihybrid Cross Green and Wrinkled Parent 
(homozygous) yyrr YYRR yr yr Parent Yellow & Round (homozygous) YR YR (F1 Generation) _ YyRr (yellow & round, heterozygous)

32. YyRr Yellow & Round Parent (heterozygous) yr yR YR Yr YR YyRr Yr Yellow & Round Parent (heterozygous) yR yr Dihybrid Cross Phenotypic Ratio 9/16 Yellow & Round : 3/16 Yellow & Wrinkled : 3/16 Green & Round : 1/16 Green & Wrinkled **Remember** Dihybrid Cross = 9 : 3 : 3 : 1

33. Examples.... 1. Black coat colour (B) in cocker spaniels is dominant to white coat colour (b). Solid coat pattern (S) is dominant to spotted pattern (s). A male that is black with a solid pattern mates with two females. The mating with female A which is white, solid, produces four pups: 2 black, solid, and two white, solid. The mating with female B, which is black, solid, produces a single pup, which is white, spotted. Indicate the genotypes of the parents.

34. 2. In guinea pigs, black coat colour (B) is dominant to white (b), and short hair length (S) is dominant to long (s). Indicate the genotypes and phenotypes from the following crosses: a) Homozygous for black, heterozygous for short-hair guinea pig crossed with a white, long-haired guinea pig. b) Heterozygous for black and short-hair guinea pig crossed with a white, long-hair guinea pig.

35. c) Homozygous for black and long-hair crossed with a heterozygous black and short-hair guinea pig.

36. 2. Discuss the relationship among chromosomes, genes, and DNA. h. Examine incomplete dominance, alleles, sex determination, and sex-linked traits in the context of human genetics. i. Discuss several human genetic disorders such as hemophilia, sickle-cell anemia, Down`s syndrome, and Tay-Sach`s disease.

37. Test Cross There is an organism showing the dominant trait but it is unknown if the 
organism is homozygous or heterozygous, it's genotype is unknown. To figure 
out the genotype you cross the unknown genotype and a homozygous recessive 
genotype. If the offspring all show the dominant trait, the unknown genotype is 
homozygous dominant. If any of the offspring show the recessive trait, the unknown genotype was 
heterozygous dominant.

39. Determine the genotype of the parent plants by looking at the phenotypes of the offspring from the following cross. Round, yellow X  Wrinkled, green 1/4 round, yellow, 1/4 round, green, 1/4 wrinkled, yellow, 1/4 wrinkled, green

40. Incomplete Dominance The lack of a dominant gene. Both alleles contribute to the phenotype of a 
heterozygote. Produces an offspring with traits unlike either parent. Ex) Red snapdragon (RR) X White snapdragon (WW) F1Generation All Pink Snapdragons (RW) RW X RW F2 Generation  R W R W 1 RR (red) : 2RW (pink) : 1 WW (white)

41. Codominance Two dominant genes are expressed at the same time in the heterozygous 
organism. Ex) Shorthorn Cattle Red (HRHR) X White (HWHW) Roan Calf - it has intermingling of white and red hair F1 Generation (all) HRHW X HRHW F2 Generation HR HW HR  Hw 1 HRHR : 2HRHW : 1HWHW

42. Multiple Alleles The problem we have dealt with so far only have dealt with 2 alleles - the 
dominant allele and the recessive allele. The dominant allele controlled 
the trait. Multiple Alleles - when more than 2 different alleles exist for a trait. Ex) the fruit fly Drosophilz - many different eye colors are possible. Red (wild type) eyes : most common  Apricot  Honey  White Dominant Hierarchy Note: a drosophila can only have 2 different genes at one time, but many alleles 
are possible.

43. When using multiple alleles we no longer use upper and lower case 
letters. Capital letters with subscript numbers are used. Red (wild type) eyes E1E1 OR E1E2, E1E3, E1E4 Apricot E2E2, E2E3, E2E4 Honey E3E3, E3E4 White E4E4

44. Ex) Human Blood Typing: example of codominance and multiple alleles The ABO blood typing system in humans is determined by a set of 3 alleles 
- multiple alleles. IA, IB, i Different combinations of these alleles in people produce 4 different blood 
types.  Type A, Type B, Type AB, Type O Genotype Phenotype IAIA or IAi Type A Blood IBIB or IBi Type B Blood IAI B Type AB Blood * ii Type O Blood * This is codominance - different alleles expressing their full phenotype in a 
heterozygote, giving a new phenotype.

45. Exceptions to Mendel's Laws Example 
Questions... 1. For ABO blood groups, the A and B genes are codominant, but both 
A and B are dominant over type O. Indicate the blood types possible 
from the mating of a male who is blood type O with a female of blood 
type AB. 2. Could a female with blood type AB ever produce a child with blood 
type AB? Could she ever have a child with blood type O?

46. Exceptions to Mendel's Laws Example 
Questions... 3. Thalassemia is a serious human genetic disorder that 
causes severe anemia. The homozygous condition (TmTm) leads to sever anemia. People with thalassemia die before sexual 
maturity. The heterozygous condition (TmTn) causes a less serious form of anemia. The genotype TnTn causes no symptoms of the disease. Indicate the possible genotypes and 
phenotypes of the offspring if a male with the genotype TmTn marries a female of the same genotype.

47. Review... 1. What is incomplete dominance? Provide an 
example. 2. What is meant by the term "multiple alleles?" 
Provide an example. 3. What is co-dominance?

48. 2. Discuss the relationship among chromosomes, genes, and DNA. h. Examine incomplete dominance, alleles, sex determination, and sex-linked traits in the context of human genetics. i. Discuss several human genetic disorders such as hemophilia, sickle-cell anemia, Down`s syndrome, and Tay-Sach`s disease.

49. Incomplete Dominance Examples... A cross between a blue blahblah bird and a white blahblah bird 
produces offspring that are sliver. The color of blahblah birds 
is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the 
original cross? b) What is/are the genotyp(s) of the silver offspring? c) What would be the phenotypic ratiosof offspring produced by two silver blahblah birds?

50. Incomplete Dominance Examples... 1. The color of fruit for Golgi plants is determined by two alleles. 
When two plants with orange fruits are crossed the following 
phenotypic ratios are present in the offspring: 25% red fruit, 50% 
orange fruit, 25% yellow fruit. What are the genotypes of the 
parent orange-fruited plants?