Category: Curriculum Map

Hardy-Weinberg Problems

 

POPULATION GENETICS AND THE HARDY-WEINBERG LAW

 

The Hardy-Weinberg formulas allow scientists to determine whether evolution has occurred. Any changes in the gene frequencies in the population over time can be detected. The law essentially states that if no evolution is occurring, then an equilibrium of allele frequencies will remain in effect in each succeeding generation of sexually reproducing individuals. In order for equilibrium to remain in effect (i.e. that no evolution is occurring) then the following five conditions must be met:

  1. No mutations must occur so that new alleles do not enter the population.
  2. No gene flow can occur (i.e. no migration of individuals into, or out of, the population).
  3. Random mating must occur (i.e. individuals must pair by chance)
  4. The population must be large so that no genetic drift (random chance) can cause the allele frequencies to change.
  5. No selection can occur so that certain alleles are not selected for, or against.

Obviously, the Hardy-Weinberg equilibrium cannot exist in real life. Some or all of these types of forces all act on living populations at various times and evolution at some level occurs in all living organisms. The Hardy-Weinberg formulas allow us to detect some allele frequencies that change from generation to generation, thus allowing a simplified method of determining that evolution is occurring. There are two formulas that must be memorized:

 

p2 + 2pq + q2 = 1 and p + q = 1

 

p = frequency of the dominant allele in the population
q = frequency of the recessive allele in the population
p2 = percentage of homozygous dominant individuals
q2 = percentage of homozygous recessive individuals
2pq = percentage of heterozygous individuals

Individuals that have aptitude for math find that working with the above formulas is ridiculously easy. However, for individuals who are unfamiliar with algebra, it takes some practice working problems before you get the hang of it. Below I have provided a series of practice problems that you may wish to try out. Note that I have rounded off some of the numbers in some problems to the second decimal place.

PROBLEM #1    You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:

  1. The frequency of the “aa” genotype.
  2. The frequency of the “a” allele.
  3. The frequency of the “A” allele.
  4. The frequencies of the genotypes “AA” and “Aa.”
  5. The frequencies of the two possible phenotypes if “A” is completely dominant over “a.”

PROBLEM #2.    Sickle-cell anemia is an interesting genetic disease. Normal homozygous individuals (SS) have normal blood cells that are easily infected with the malarial parasite. Thus, many of these individuals become very ill from the parasite and many die. Individuals homozygous for the sickle-cell trait (ss) have red blood cells that readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often die because of the genetic defect. However, individuals with the heterozygous condition (Ss) have some sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well within these “partially defective” red blood cells. Thus, heterozygotes tend to survive better than either of the homozygous conditions. If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene?

PROBLEM #3.    There are 100 students in a class. Ninety-six did well in the course whereas four blew it totally and received a grade of F. Sorry. In the highly unlikely event that these traits are genetic rather than environmental, if these traits involve dominant and recessive alleles, and if the four (4%) represent the frequency of the homozygous recessive condition, please calculate the following:

  1. The frequency of the recessive allele.
  2. The frequency of the dominant allele.
  3. The frequency of heterozygous individuals.

PROBLEM #4.    Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on an exam, calculate the following:

  1. The percentage of butterflies in the population that are heterozygous.
  2. The frequency of homozygous dominant individuals.

PROBLEM #5.     A rather large population of Biology instructors have 396 red-sided individuals and 557 tan-sided individuals. Assume that red is totally recessive. Please calculate the following:

  1. The allele frequencies of each allele.
  2. The expected genotype frequencies.
  3. The number of heterozygous individuals that you would predict to be in this population.
  4. The expected phenotype frequencies.
  5. Conditions happen to be really good this year for breeding and next year there are 1,245 young “potential” Biology instructors. Assuming that all of the Hardy-Weinberg conditions are met, how many of these would you expect to be red-sided and how many tan-sided?

PROBLEM #6.    A very large population of randomly-mating laboratory mice contains 35% white mice. White coloring is caused by the double recessive genotype, “aa”. Calculate allelic and genotypic frequencies for this population.

PROBLEM #7.    After graduation, you and 19 of your closest friends (lets say 10 males and 10 females) charter a plane to go on a round-the-world tour. Unfortunately, you all crash land (safely) on a deserted island. No one finds you and you start a new population totally isolated from the rest of the world. Two of your friends carry (i.e. are heterozygous for) the recessive cystic fibrosis allele (c). Assuming that the frequency of this allele does not change as the population grows, what will be the incidence of cystic fibrosis on your island?

PROBLEM #8.    You sample 1,000 individuals from a large population for the MN blood group, which can easily be measured since co-dominance is involved (i.e., you can detect the heterozygotes). They are typed accordingly:

 

BLOOD TYPE GENOTYPE NUMBER OF INDIVIDUALS RESULTING FREQUENCY
M MM 490 0.49
MN MN 420 0.42
N NN 90 0.09

 

Using the data provide above, calculate the following:

  1. The frequency of each allele in the population.
  2. Supposing the matings are random, the frequencies of the matings.
  3. The probability of each genotype resulting from each potential cross.

PROBLEM #9.    Cystic fibrosis is a recessive condition that affects about 1 in 2,500 babies in the Caucasian population of the United States. Please calculate the following:

  1. The frequency of the recessive allele in the population.
  2. The frequency of the dominant allele in the population.
  3. The percentage of heterozygous individuals (carriers) in the population.

PROBLEM #10.    In a given population, only the “A” and “B” alleles are present in the ABO system; there are no individuals with type “O” blood or with O alleles in this particular population. If 200 people have type A blood, 75 have type AB blood, and 25 have type B blood, what are the allelic frequencies of this population (i.e., what are p and q)?

PROBLEM #11.    The ability to taste PTC is due to a single dominate allele “T”. You sampled 215 individuals in biology, and determined that 150 could detect the bitter taste of PTC and 65 could not. Calculate all of the potential frequencies.

ANSWERS

Genetic Traits Activity

 

Finding Your Genetic Match

Introduction:

Have you ever noticed that brothers or sisters often look alike?  Their inherited traits are what make their physical appearance so similar. An inherited trait is a particular genetically determined characteristic that distinguishes a person. The traits of children are determined by the traits that  are passed on from their parents. Some traits are obvious in a family — a child’s nose is shaped like their mother’s nose, but some traits are less obvious. You may have similar traits to many of your classmates even though you are not related to them. Some examples of often un-noticed human traits are the ability or not to roll your tongue, attached or unattached earlobes, dimples or freckles, naturally curly or straight hair, hitchhiker’s or straight thumb, straight or widow’s peak hairline, smooth or cleft chin, or colorblindness or normal vision.

There are numerous traits in humans, but some traits occur more frequently than others.  Between 70-90% of the human population have free-hanging earlobes, can roll their tongue,  are right-handed, and can taste a chemical called PTC.  These traits are called high frequency traits.

Objective:

Students will determine the presence of certain high frequency traits in themselves & their classmates.

Materials:

Genetic Inventory sheet with pictures, paper, pencil, PTC taste strips.

Procedure:

  1. Identify which of the following 10 human traits you have by placing a check mark beside that trait.
  2. Compare the traits you have with other students in the classroom and find the student you most closely match.

 

 

Human Trait Inventory
Student:
Tongue Roller
Non-Tongue Roller
Attached Earlobes
Unattached earlobes
Dimples
No Dimples
Right-handed
Left-Handed
Widow’s Peak
Straight Hairline
Left Thumb on top when Hands Crossed
Right Thumb on top when Hands Crossed
Hair on mid-digit of hand
No hair on mid-digit of hand
Bent little finger
Straight little finger
Second toe longer than big toe
Second toe not longer than big toe
Can Taste PTC
Can Not Taste PTC
Vulcan (Fingers spread 2 by 2)
None Vulcan
Class Match:

 

 

 

Tongue Roller Non Roller Dimples No Dimples
Attached Earlobes Unattached Earlobes Widow’s Peak Straight Hairline
Longer Second Toe Short Second Toe Bent Little finger Hitchhiker’s Thumb
Attached Ear lobes (left)
Unattached ear Lobes (right)		 “VULCAN” or No “VULCAN” Dimples Right/Left Thumb on top

 

Genetics PPT Questions

 

 

Mendelian Genetics
PowerPoint Questions
Gregor Mendel

1. Who is responsible for our laws of inheritance?

2. What organism did Mendel study?

3. When was Mendel’s work recognized?

4. When did Mendel perform his experiments & how many plants did he grow?

5. What did Mendel notice about offspring traits?

6. How is Mendel referred to today?

7. In what country did Mendel do his research on peas?

8. Mendel stated that physical traits were inherited as _______________.

9. Today we know that particles are actually what?

Terminology

10. Define these three terms:
a. trait –

 

b. heredity –

c. genetics –

 

11. Name & describe two types of genetic crosses.

 

 

12. What is used to solve genetic crosses?

13. Sketch a Punnett square & show how they are  used to solve a genetics problems.

 

 

 

14. Use a Punnett square to solve a cross between two parents that both have the genotype Yy.

 

 

 

 

15. What are alleles & what are the two forms?

 

16. Explain the difference between dominant & recessive alleles.

 

 

17. Using a letter of the alphabet, show how each allele would be represented.

 

18. What is a genotype and write 3 possible genotypes?

 

19. What is a phenotype and write possible phenotypes for your genotypes in question 18?

 

20. Using these alleles, R = red flower and r = yellow flowers, write all possible genotypes & phenotypes.

 

21. What are homozygous genotypes?

 

22. Write a homozygous dominant genotype.

23. Write a homozygous recessive genotype.

24. What is meant by a heterozygous genotype?

 

25. Write a heterozygous genotype.

26. Heterozygous  genotypes are also called _____________.

27. What two things actually determine an organism’s characteristics?

Pea Experiments

28. Give 4 reasons that Mendel used garden peas, Pisum sativum, for his experiments.

 

 

 

29. Name the male and female parts of a flowering plant and explain how pollination occurs.

 

 

30. What is the difference between self and cross pollination?

 

31. Explain how Mendel cross pollinated his pea plants.

 

 

32. How did Mendel get pure plants?

33. Name 8 pea plant traits and give the dominant & recessive form of each.

 

 

 

 

 

34. How did Mendel’s experimental results compare to the theoretical genotypic ratios? Explain.

 

35. What does P1 mean?

36. What is the F1 generation?

37. What is the F2 generation?

38. What results from this cross — TT  x  tt?

39. What results do you get from crossing two hybrids (Tt   x  Tt)?

 

40. Show all your work for solving a P1 monohybrid cross for seed shape.
Trait:
Alleles:

P1 cross:  __________ x __________

Genotype ____________
Phenotype ___________
G. Ratio _____________
P. Ratio _____________

 

41. The offspring of the above cross are called the _____ generation.

42. Show all your work for solving a F1 monohybrid cross for seed shape.
Trait:
Alleles:

F1 cross:  __________ x __________

Genotype ____________
Phenotype ___________
G. Ratio _____________
P. Ratio _____________

43. Show all your work for solving both F2 monohybrid crosses for seed shape.

Trait:
Alleles:

F2 cross:  ________ x ________  F2 cross:  ________ x ________

 

 

 

 

Genotype ____________                  Genotype ____________
Phenotype ___________                   Phenotype ___________
G. Ratio _____________                   G. Ratio _____________
P. Ratio _____________                    P. Ratio _____________

Mendel’s Laws

Complete the following question:

44. _________ are responsible for inherited traits.

45. Phenotype is based on _______________.

46. Each trait requires _____ genes, one from each ____________.

47. State the Law of Dominance and give an example.

 

 

48. State the Law of Segregation and tell when alleles are “recombined”.

 

 

49. State the Law of Independent assortment & tell what type of crosses show this.

 

 

50. Using the formula 2n where n = the number of heterozygotes, tell how many gametes will be produced by each of the following allele combinations:
a. RrYy
b. AaBbCCDd
c. MmNnOoPPQQRrssTtQq

51. What are the possible allele combinations in the egg and sperm from the following cross — RrYy x RrYy.

 

52. Show how to work an F1 dihybrid cross for seed shape & seed color.

Traits:
Alleles:

 

 

F1 cross   __________ x __________

 

 

 

GR         Genotypes           PR         Phenotypes

 

 

 

 

 

 

 

 

53. Complete this cross or crosses for eye color & curliness of the hair — bbC__ x bbcc.

 

 

 

 

54. Draw a table summarizing Mendel’s 3 laws.

 

 

 

 

 

 

Incomplete and Co-Dominance

55. Incomplete dominance occurs in __________ and produces a phenotype _______________ the phenotype of the two parents.

56. Show your work solving a cross for flower color in snapdragons when there is incomplete dominance.

Trait:
Alleles:

Cross:  RR x rr

 

Genotype ____________
Phenotype ___________
G. Ratio _____________
P. Ratio _____________

57. What is codominance & give an example?

 

58. Write the genotypes for each of these blood types:

type A
type B
type AB
type O

59. Solve this codominance problem: IBIB x IAi.

 

 

 

60. Solve this codominance problem for blood type: ii x IAIB.

 

 

 

Sex-Linked Traits

61. What are sex linked traits?

 

62. Name the sex chromosomes.

63. Write the genotype for male and for female.

64. Most sex-linked traits are carried on what chromosome?

65. Give an example of a sex-linked trait in fruit flies.

66. Show the results of crossing a red-eyed male (XRY)  with a white-eyed female (XrXr) fruit fly.
RR =
Rr =
rr =
XY =
XX =

Cross:    __________ x __________

 

 

 

Genotype ____________
Phenotype ___________
G. Ratio _____________
P. Ratio _____________

67. What is meant by a female carrier?

 

68. Name a disease that can be carried in this manner.

 

 

 

Gastric Bacteria

 

The Nobel Prize in Physiology or Medicine for 2005

jointly to

Barry J. Marshall and J. Robin Warren

for their discovery of

“the bacterium Helicobacter pylori and its role in gastritis and peptic ulcer disease”

 

 Introduction

This year’s Nobel Laureates in Physiology or Medicine made the remarkable and unexpected discovery that inflammation in the stomach (gastritis) as well as ulceration of the stomach or duodenum (peptic ulcer disease) is the result of an infection of the stomach caused by the bacterium Helicobacter pylori.

Robin Warren (born 1937), a pathologist from Perth, Australia, observed small curved bacteria colonizing the lower part of the stomach (antrum) in about 50% of patients from which biopsies had been taken. He made the crucial observation that signs of inflammation were always present in the gastric mucosa close to where the bacteria were seen.

Barry Marshall (born 1951), a young clinical fellow, became interested in Warren’s findings and together they initiated a study of biopsies from 100 patients. After several attempts, Marshall succeeded in cultivating a hitherto unknown bacterial species (later denoted Helicobacter pylori) from several of these biopsies. Together they found that the organism was present in almost all patients with gastric inflammation, duodenal ulcer or gastric ulcer. Based on these results, they proposed that Helicobacter pylori is involved in the aetiology of these diseases.

Even though peptic ulcers could be healed by inhibiting gastric acid production, they frequently relapsed, since bacteria and chronic inflammation of the stomach remained. In treatment studies, Marshall and Warren as well as others showed that patients could be cured from their peptic ulcer disease only when the bacteria were eradicated from the stomach. Thanks to the pioneering discovery by Marshall and Warren, peptic ulcer disease is no longer a chronic, frequently disabling condition, but a disease that can be cured by a short regimen of antibiotics and acid secretion inhibitors.

Peptic ulcer – an infectious disease!

This year’s Nobel Prize in Physiology or Medicine goes to Barry Marshall and Robin Warren, who with tenacity and a prepared mind challenged prevailing dogmas. By using technologies generally available (fibre endoscopy, silver staining of histological sections and culture techniques for microaerophilic bacteria), they made an irrefutable case that the bacterium Helicobacter pylori is causing disease. By culturing the bacteria they made them amenable to scientific study.

In 1982, when this bacterium was discovered by Marshall and Warren, stress and lifestyle were considered the major causes of peptic ulcer disease. It is now firmly established that Helicobacter pylori causes more than 90% of duodenal ulcers and up to 80% of gastric ulcers. The link between Helicobacter pylori infection and subsequent gastritis and peptic ulcer disease has been established through studies of human volunteers, antibiotic treatment studies and epidemiological studies.

Helicobacter pylori causes life-long infection

Helicobacter pylori is a spiral-shaped Gram-negative bacterium that colonizes the stomach in about 50% of all humans. In countries with high socio-economic standards infection is considerably less common than in developing countries where virtually everyone may be infected.

Infection is typically contracted in early childhood, frequently by transmission from mother to child, and the bacteria may remain in the stomach for the rest of the person’s life. This chronic infection is initiated in the lower part of the stomach (antrum). As first reported by Robin Warren, the presence of Helicobacter pylori is always associated with an inflammation of the underlying gastric mucosa as evidenced by an infiltration of inflammatory cells.

The infection is usually asymptomatic but can cause peptic ulcer!

The severity of this inflammation and its location in the stomach is of crucial importance for the diseases that can result from Helicobacter pylori infection. In most individuals Helicobacter pylori infection is asymptomatic. However, about 10-15% of infected individuals will some time experience peptic ulcer disease. Such ulcers are more common in the duodenum than in the stomach itself. Severe complications include bleeding and perforation.

The current view is that the chronic inflammation in the distal part of the stomach caused by Helicobacter pylori infection results in an increased acid production from the non-infected upper corpus region of the stomach. This will predispose for ulcer development in the more vulnerable duodenum.

Malignancies associated with Helicobacter pylori infection

In some individuals Helicobacter pylori also infects the corpus region of the stomach. This results in a more widespread inflammation that predisposes not only to ulcer in the corpus region, but also to stomach cancer. This cancer has decreased in incidence in many countries during the last half-century but still ranks as number two in the world in terms of cancer deaths.

Inflammation in the stomach mucosa is also a risk factor for a special type of lymphatic neoplasm in the stomach, MALT (mucosa associated lymphoid tissue) lymphoma. Since such lymphomas may regress when Helicobacter pylori is eradicated by antibiotics, the bacterium plays an important role in perpetuating this tumour.

 Disease or not – interaction between the bacterium and the human host

Helicobacter pylori is present only in humans and has adapted to the stomach environment. Only a minority of infected individuals develop stomach disease. After Marshall’s and Warren’s discovery, research has been intense. Details underlying the exact pathogenetic mechanisms are continuously being unravelled.

The bacterium itself is extremely variable, and strains differ markedly in many aspects, such as adherence to the gastric mucosa and ability to provoke inflammation. Even in a single infected individual all bacteria are not identical, and during the course of chronic infection bacteria adapt to the changing conditions in the stomach with time.

Likewise, genetic variations among humans may affect their susceptibility to Helicobacter pylori. Not until recently has an animal model been established, the Mongolian gerbil. In this animal, studies of peptic ulcer disease and malignant transformation promise to give more detailed information on disease mechanisms.

Antibiotics cure but can lead to resistance

Helicobacter pylori infection can be diagnosed by antibody tests, by identifying the organism in biopsies taken during endoscopy, or by the non-invasive breath test that identifies bacterial production of an enzyme in the stomach.

An indiscriminate use of antibiotics to eradicate Helicobacter pylori also from healthy carriers would lead to severe problems with bacterial resistance against these important drugs. Therefore, treatment against Helicobacter pylori should be used restrictively in patients without documented gastric or duodenal ulcer disease.

Microbial origin of other chronic inflammatory conditions?

Many diseases in humans such as Crohn’s disease, ulcerative colitis, rheumatoid arthritis and atherosclerosis are due to chronic inflammation. The discovery that one of the most common diseases of mankind, peptic ulcer disease, has a microbial cause, has stimulated the search for microbes as possible causes of other chronic inflammatory conditions.

Even though no definite answers are at hand, recent data clearly suggest that a dysfunction in the recognition of microbial products by the human immune system can result in disease development. The discovery of Helicobacter pylori has led to an increased understanding of the connection between chronic infection, inflammation and cancer.

Source: http://nobelprize.org/nobel_prizes/medicine/laureates/2005/press.html