pedigree pogil activity real 1 PDF

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Pedigrees How do scientists trace hereditary diseases through a family history?

Why? Imagine you want to learn about an inherited genetic trait present in your family. How would you find out the chances of passing the trait to your children? To do this, genetic counselors often prepare a pedigree, a chart that shows how a trait is inherited over several generations in a family.

Model 1 – Pedigree of Sickle Cell in Four Generations

1. What does the circle shape represent? affected and unaffected females 2. What does the square shape represent? affected and unaffected males 3. The pedigree represents the occurrence of sickle cell disease in a family. How are individuals with sickle cell represented in the pedigree? filled in with black instead of a blank space 4. Determine how parents are shown in a pedigree. (Include a picture and a description) a line drawn between indicates parents

5. Determine how children are shown in a pedigree. (Include a picture and a description) a line drawn down from the parents indicate children

Pedigrees

Adapted from Pedigrees POGIL by Summers 2012

6. How many siblings does the patient have? 5 siblings 7. If you are the patient, what is the relationship of the people in Generation I to you? great grandparents 8. Describe the phenotype of the patient. affected by sickle cell 9. Considering that the sickle cell allele is recessive, give a probable genotype for the patient. ss 10. Based on your answers for 8 and 9, determine the phenotype and genotype of the patient’s parents.

Ss, affected with sickle cell

11. Draw a pedigree below for the following information. Be sure to include the generation numbers! A girl with a recessive genetic disease has two sisters and one brother. Her brother has the same disease, but her sisters do not. Her mother has the disease, but her father does not.

I

II

12. How could a pedigree be used by a genetic counselor? It could be used to determine the chances of a child inheriting traits and disorders that would be considered unfavorable based on parental genetics.

Pedigrees

Adapted from Pedigrees POGIL by Summers 2012

Read This! Scientists can use pedigrees to determine if a disease is caused by a dominant or recessive allele. Pedigrees are helpful if family members want to know if they are carriers or if their children might get a genetic disease. Carriers are individuals who are heterozygous for a genetic disease, but do not show symptoms of the disorder. Carriers can pass the allele for the disease to their offspring.

Model 2 – Pedigree Case Studies Case 1

[ DOMINANT/RECESSIVE/UNKNOWN]

Case 2

Case 3

[ DOMINANT/RECESSIVE/UNKNOWN]

[ DOMINANT/RECESSIVE/UNKNOWN]

13. Why are some people known as “carriers”? they carry genes for a disease but show no symptoms 14. For Case # 1, use a guess-and-check method to determine whether the disease is dominant, recessive, or unknown. Under each circle or square, write the genotypes for each person. Use “A” for dominant allele and “a” for recessive allele. You may use “A-” if you cannot determine the whole genotype. Explain the reasoning for your choice for Case 1 below. The disease is recessive. Only one child out of the three have the disease and the parents don't show any symptoms. The parents were carriers, showing that they were heterozygous dominant. That's why they only had one out of their three children have the disease. 15. For Case # 2, use a guess-and-check method to determine whether the disease is dominant, recessive, or unknown. Write the genotypes for each person, as you did for Case #1. Explain the reasoning for your choice for Case 2 below. The parents are positive for the disease but all the children are negative. This is possible if the disease was dominant and both of the parents were heterozygous dominant. It is only a possibility but there is about a 2% chance of all the children being homozygous recessive. 16. For Case # 3, use a guess-and-check method to determine whether the disease is dominant, recessive, or unknown. Write the genotypes for each person, as you did for Case #1. Explain the reasoning for your choice for Case 3 below. The disease might be dominant. One parent was positive for it while the other was negative, yet most of the children are positive for it. If the disease was dominant, the negative father would be homozygous recessive, making the positive mother either a heterozygous or homozygous dominant. This rationalizes the majority of the children being positive.

Pedigrees

Adapted from Pedigrees POGIL by Summers 2012

Model 3 – Pedigree of Hemophilia in a Royal Family

17. Identify the gender and phenotypes of Beatrice and Henry’s children. four boys, one girl first boy: no hemophilia Leopold: hemophilia Eugene: no hemophilia 18. Beatrice’s daughter, Eugenie, married Alfonso XIII of Spain. Identify the gender and phenotype of their children. six children; four boys, two girls second boy: no hemophilia first girl: no hemophilia second girl: no hemophilia Gonzalo: hemophilia fourth boy: no hemophilia

19. Based on the model, is hemophilia a dominant or recessive condition? Explain your reasoning. Hemophilia is a recessive trait because you see that hemophilia skips generations. This can also be determined from the genotypes since Maurice and Leopold are affected. They must have the genotype "aa" for them to get affected, but their parents aren't the cause because they are heterozygous (Aa). This is reasonable because the rest of their children are affected meaning that they either have the genotype of AA or Aa;

Pedigrees

Adapted from Pedigrees POGIL by Summers 2012

20. Using model 3, complete the following table: # with hemophilia

Total # of individuals

% with hemophilia

Females

0

11

0

Males

4

11

36.36

21. Using the information in model 3 and your answers to prior questions, explain similarities and differences between model 3 and model 1. Similarities

- four generations - recessive

Differences

- less number of people - model 1 has less people affected - model 3 has more people affected

Read This! The nuclei of human cells contain 22 pairs of autosomes and a pair of sex chromosomes. In females the two sex chromosomes are XX and in males the sex chromosomes are XY. Unlike the autosomes, the X and Y chromosomes are non-homologous with the X likely containing around 800-900 genes that code for proteins compared to the Y chromosomes with only 50-60 genes. As a result, most sex-linked alleles are encoded on the X chromosome. Pedigree charts can be analyzed to determine if the allele causing a condition is located on an autosome or the sex chromosome.

22. Using the information in Read This above and model 3, is the hemophilia allele located on an autosome or sex chromosome? Explain your reasoning. The hemophilia is located on a sex chromosome because the abnormal gene responsible for hemophilia is carried on the X chromosome.

Pedigrees

Adapted from Pedigrees POGIL by Summers 2012

Extension Questions Imagine you are a genetic counselor and a couple has asked you to determine the probability of their child developing a genetic disease, given their family history below. Husband’s family history:  The husband has the disease.  The family history of the husband is unknown. Wife’s family history:  The wife does not have the disease.  The wife has a sister without the disease and a brother with the disease.  Both of the wife’s parents have the disease.  The wife’s father is an only child; his father has the disease, but his mother does not.  The wife’s mother has two brothers without the disease; her mother had the disease, but her father did not.

23. Translate the family history into a pedigree using standard notations and symbols. Hint: Work as a group to do a rough draft on scratch paper first! Aa

AA

AA

AA

AA

AA A-

AA

A-

A-

AAA

24. Circle one: This disease is [ DOMINANT / 25. Circle one: This disease is [

]. /SEX-LINKED ].

26. Explain how you know the disease allele is dominant or recessive. Use specific relationships (between family members) to support your claim. This is a recessive disease because the wife's mother got the disease from both of her parents and the wife's father got the disease from his father.

27. Explain how you know the disease allele is autosomal or sex-linked. Use specific relationships (between family members) to support your claim. This is an autosomal disease because it traces back to both of the wife's parents.

28. Add genotypes to each family member on your pedigree for #23. Use “A” for dominant allele and “a” for recessive allele. You may use “A-” if you cannot determine the whole genotype. Pedigrees

Adapted from Pedigrees POGIL by Summers 2012

29. If the husband is heterozygous for the disease-causing allele, what is the probability that their child will develop the disease? Include a Punnett Square and a genotypic and phenotypic ratio in your answer. aa AA There is a 75% chance of the offspring developing the disease. Aa AA AA

aa

Aa

aa

30. If the husband is homozygous for the disease-causing allele, what is the probability that their child will develop the disease? Include a Punnett Square and a genotypic and phenotypic ratio in your answer. aa AA There is a 50% chance of the offspring developing the disease. AA

AA

Aa

aa

Aa

aa

31. Based on your analysis of the husband and wife’s family histories, what predications can you give the couple about the probability of their future offspring in relation to the husband’s genetic disease? Their future offspring will most likely get the disease since it runs in the family. Most of the child's maternal great-grandparents had the disease and so do both of their maternal grandparents.

Pedigrees

Adapted from Pedigrees POGIL by Summers 2012...