Lab 2 – Inheritance & Evolution
Purpose
Lab 2 will help you apply genetic and mathematical principles to predict the inheritance of Mendelian traits through family lines and explain evolutionary change in human populations.
Skills
Lab 2 builds the following skills that are essential to success in this class:
· Pedigree and Punnett square interpretation – predicting inheritance patterns for Mendelian traits.
· Population Genetics – applying mathematical principles to identify evolutionary change.
Knowledge
The methods we practice in Lab 2 will clarify the mechanisms of inheritance responsible for some of the biological traits present in you and/or genetic family members, and teach you how to identify evolutionary change with math. These skills are essential in several professions, especially in the fields of medicine, animal husbandry, and conservation biology.
Part A – Inheritance
Task
Use the family information provided below for each “Case Study” couple to draw a pedigree diagram and answer the questions provided. You may draw your pedigrees by hand or use your preferred electronic device to create them. Be sure to label your pedigrees with their associated Case Study ID (A, B, C). To receive full credit for this portion of the lab, each pedigree diagram must:
· Include all family members whose trait information is provided in the Case Study
· Identify the genotypes for all individuals, using the letters specified in the Case Study
· Identify all “affected” individuals (i.e. those who have the trait) with a shaded symbol
· Be submitted in Canvas as a separate file attachment or embedded within this worksheet. Photo files of hand-drawn pedigrees are acceptable.
Case Study A
Maria and Arjun are having twins, a boy and a girl. Although neither Maria nor Arjun have sickle cell anemia, the condition runs in both of their families. The couple is aware that sickle cell anemia, like other autosomal recessive traits, can “skip” generations, and so they are looking for information about their “risk” of passing the condition on to their twins. After speaking to the couple about their family history, you are given the following information to help you create a pedigree and better assess their likelihood of passing sickle cell anemia onto their children:
Maria
Maria comes from a family of four, including herself. Maria and her mother are carriers for the sickle cell trait, and her only sibling, a brother, has the condition. To her knowledge, the only other family member to have the condition is her paternal grandfather (her dad’s dad).
Arjun
Arjun is also one of two children in his family. He, his brother, and his mother do not have sickle cell anemia. In fact, Arjun’s mother has no family history of the condition at all. However, Arjun’s father is affected, and inherited the condition from his carrier parents (Arjun’s paternal grandparents).
1. Complete your pedigree of Maria and Arjun’s families and include everyone’s genotype for the sickle cell trait using a capital “A” for the dominant allele, and a lowercase “a” for the recessive allele.
2. Cross Maria and Arjun’s genotypes for the sickle cell trait using the Punnett square provided below:
3. Based on your Punnett square, what is the likelihood that Maria and Arjun will have a child with sickle cell anemia?
Case Study B
Lionel and Hui Yin are thinking about starting a family. Lionel recently discovered that Huntington’s disease, an autosomal dominant condition that affects the brain, runs in his family. Lionel is too young for symptoms of the disease to be apparent and is apprehensive about undergoing genetic screening. He and Hui Yin are seeking genetic counseling to find a less invasive way to assess their risk of producing a child with Huntington’s disease, and have agreed upon pedigree analysis. They provide the following information about their family history:
Lionel
Lionel was adopted as a small baby, and recently became reunited with his biological mother and sister. His sister has Huntington’s disease, but they are certain it was not inherited from their mother, who is 55 years old and has never had any symptoms. The condition must have come from the siblings’ father, who is now deceased. He got the condition from his father, Lionels’ paternal grandfather.
Hui Yin
Hui Yin is an only child, with no known family history of Huntington’s disease.
4. Complete your pedigree of Lionel and Hui Yin’s families. Assume that Lionel is heterozygous for Huntington’s disease and include all genotypes for this trait using a capital “H” for the dominant allele, and a lowercase “h” for the recessive allele.
5. Cross Lionel’s genotype with Hui Yin’s using the Punnett square provided below, assuming that Lionel is heterozygous for Huntington’s disease.
6. Based on your Punnett square, what is the likelihood that Lionel and Hui Yin will produce a child that will
NOT
be at risk for developing Huntington’s disease as an adult?
Case Study C
Paula and David are pregnant, and just learned that their baby has two X chromosomes. They visit a genetic counselor with concerns about passing hemophilia to their baby, as this X-linked recessive condition is present in both of their families. They decide to pursuit pedigree analysis to assess their child’s risk before undergoing prenatal testing to screen for the genetic variants associated with the condition. They provide you with the following information about their family histories:
Paula
Paula is one of three siblings and a carrier for hemophilia. Her mother and sister are also carriers, but her father is completely unaffected. The only person in her family to have the condition is her brother.
David
David has two sisters, both with hemophilia. Although David and his mother do not have the condition, his father did. In addition to the baby on the way, Paula and David have two sons, one of whom was diagnosed with hemophilia shortly after birth.
7. Complete your pedigree for Paula and David’s families, and record everyone’s genotype for hemophilia using a capital “B” for the dominant allele, and a lowercase “b” for the recessive allele.
Because hemophilia is an X-linked trait, you will need to include the sex chromosomes in the genotypes (e.g. XBXB, XBXb, XbXb, XBY, XbY)
8. Cross Paula and David’s genotypes for hemophilia using the Punnett square provided below. Be sure that you add the sex chromosomes to your genotypes and cross them along with their alleles.
9. What is the likelihood that Paula and David will pass hemophilia to their unborn female? What would the chances be if the child was male?
Answer questions 10 – 15 using the data tables and Pedigrees D – E provided below.
Pedigree D
10. Identify the inheritance pattern shown in Pedigree D [autosomal dominant; autosomal recessive; X-linked dominant; X-linked recessive]:
11. Identify two characteristics you observe in Pedigree D to support your answer for #10.
12. Complete the Pedigree D Data Table provided below:
Individual |
Genotype [DD, Dd, dd] |
|
1 |
|
|
3 |
|
|
4 |
|
|
7 |
Pedigree E
13. Identify the inheritance pattern shown in Pedigree E [autosomal dominant; autosomal recessive; X-linked dominant; X-linked recessive]:
14. Identify two characteristics you observe in Pedigree E to support your answer for #13.
15. Complete the Pedigree E Data Table provided below:
Individual |
Genotype [EE, Ee, ee] |
|
2 |
|
|
5 |
|
|
8 |
|
|
11 |
Part B – Evolution
Task
In this part of Lab 2 we will apply the Hardy Weinberg Equilibrium Equation to allele frequency data for two real human populations. Using our calculations in combination with some historical information about these groups, we’ll work to identify genetic change over time and the possible forces that might be at play.
· Answer questions SOME NUMBER TO SOME NUMBER, based on the Case Study information provided.
· When completing your calculations, please rshow all your work and round your answers to three decimal places (0.001). If you do not have a calculator with the square root function, you can use the
Google Calculator for free online.
Case Study F
The sickle cell allele first emerged when there was a change in the sequence of DNA bases in the gene that produces hemoglobin – a substance in the red blood cells that transports oxygen throughout the body. This change is inherited in a Mendelian fashion from one generation to the next. Individuals who have the sickle cell allele have a greater resistance to malaria, but may also suffer from a disease known as sickle cell anemia (SCA).
SCA was very rare in Nigeria before malaria was widespread in the country, with an estimated frequency of one in every 1000 births. This disease disrupts the transport of oxygen throughout the body and can cause severe damage to the organs, leading to premature death. SCA affects men and women with equal frequency, and unaffected parents (both mothers and fathers) can have affected offspring of either sex.
Case Study F Questions
16. Determine the inheritance pattern for SCA and explain how you arrived at your answer.
17. Use the pre-malaria rate of SCA given above and the Hardy Weinberg Equation (p2 + 2pq + q2 = 1) to determine the expected genotype frequencies in present-day Nigeria. Let the capital letter “A” and lowercase “a” represent the alleles involved. Show your work below:
Since malaria became endemic in Nigeria some 3,000 years ago, SCA has become more common. The present-day genotype frequencies for SCA in Nigeria are:
SCA allele frequency data, Nigeria
|
Genotype |
Frequency |
|
Homozygous dominant (AA) |
0.687 |
|
Heterozygous (Aa) |
0.284 |
|
Homozygous recessive (aa) |
0.029 |
18. Compare the observed allele frequencies in the table to the expected values calculated for #17. How do they differ?
19. What evolutionary force(s) might be responsible for the differences you described in #18? Be sure to support your answer with information from the Case Study and Module 2.
Case Study G
Pingelap atoll is a remote island in the South Pacific. In 1780, a typhoon killed 90% of the population, leaving just 30 surviving individuals. One of the survivors, a man named Nahnmwarki Mwanenised, had a rare form of color-blindness known as achromatopsia. Acromatopsia is a Mendelian genetic trait that causes complete color-blindness, so that affected individuals are only able to see in white, black, and shades of grey.
Prior to the typhoon, it is estimated that achromatopsia affected one in every 100 births. Males and females are affected with equal frequency, and it is very common for unaffected parents (both mothers and fathers) to have affected offspring of either sex.
Case Study G Questions
20. Determine the inheritance pattern of achromatopsia and explain how you arrived at your answer.
21. Use the rate of achromatopsia in the pre-typhoon population given above and the Hardy Weinberg Equilibrium Equation (p2 + 2pq + q2) to determine the expected genotype frequencies for achromatopsia in the present-day Pingelap population. Let the capital “H” and lowercase “h” represent the alleles involved. Show your work below:
The present-day genotype frequencies for achromatopsia in the Pingelap population are:
Achromatopsia allele data, Pingelap
|
Genotype |
Frequency |
|
Homozygous dominant (HH) |
0.602 |
|
Heterozygous (Hh) |
0.348 |
|
Homozygous recessive (hh) |
0.050 |
22. Compare the observed allele frequencies in the table with the expected values you calculated in #21. How do they differ?
23. What evolutionary force(s) might be responsible for the differences you described in #22? Be sure to support your answer with information from the Case Study and Module 2.
1
