Objective: Determine the identity of the Mystery Donor
Snapshot of Procedure
1. Read the Summary of Evidence Report
2. Determine genotype of hand print left at the courthouse by completing the ‘Differences in Similar Phenotypes’ HOT Lab.
3. Read ‘The Genetics of Eye Color’ article to determine the probable eye color of mystery donor.
4. ‘Can Chromosomal Abnormalities Be Observed?’ – HOT lab (look at Figures 1, 4 and 5)
5. Then complete the karyotype analysis of the mystery donor and compare to the provided karyotypes.
6. Identify the donor with explanation on how you came to your conclusion.
Differences in Similar Phenotypes
NGSSS:
SC.912.L.16.1 Use Mendel’s Laws of Segregation and Independent Assortment to analyze patterns of inheritance. AA
SC.912.L.16.2 Discuss observed inheritance patterns caused by various modes of inheritance, including dominant, recessive, co-dominant, sex-linked, polygenic, and multiple alleles.
Background:
Humans are classified as a separate species because of all the special characteristics that they possess. These characteristics are controlled by strands of DNA located deep inside their cells. This DNA contains the code for every protein that an organism has the ability to produce. These proteins combine with other chemicals within the body to produce the cells, tissues, organs, organ systems, and finally the organism itself. The appearance of these organs, such as the shape of one’s nose, length of the fingers, or the color of the eyes is called the phenotype. Even though humans contain hands with five fingers, two ears, or one nose, there are subtle differences that separate these organs from one another. There are subtle differences in a person’s genes that allows for these different phenotypes. In this lab, we are going to observe some of these differences in phenotype and try to determine why they happened.
Problem Statement: Do all human hands measure the same?
Vocabulary: alleles, dominant, genotype, homozygous, heterozygous (hybrid), phenotype, recessive
Materials (per group):
· Metric ruler
· Meter stick
Procedures:
Hand Measurement:
All human hands look pretty much alike. There are genes on your chromosomes that code for the characteristics making up your hand. We are going to examine two of these characteristics: hand width and hand length.
1. Choose a partner and, with a metric ruler, measure the length of their right hand in centimeters, rounding off to the nearest whole centimeter. Measure from the tip of the middle finger to the beginning of the wrist. Now have your partner do the same to you. Record your measurements in Table 1.
2. Have your partner measure the width of your hand, straight across the palm, and record the data in Table 1. Have your partner do the same to you.
Table 1 - Group Data on Right Hand Width and Length
Name: ______/ Name: ______Length of Hand ______cm. / Length of Hand ______cm.
Width of Hand ______cm. / Width of hand ______cm.
Class Data: After the entire class has completed Table 1, have the students record their data on the board in the front of the room. Use Table 2 below to record the data for your use. Extend the table on another sheet of paper if needed.
Table 2 - Class Data on Right- Hand Width and Length
Student / Gender M/F / Hand Length (cm) / Hand Width (cm)M / F
M / F
M / F
M / F
M / F
M / F
M / F
M / F
M / F
M / F
M / F
Tabulate the results of your class measurements by totaling the number of males and females with each hand length and width and entering these totals in the tables below.
Table 3 - Class Hand Length
Measurement of Hand Length in cm. / # of Males / # of Females / Total No. of Males and FemalesTable 4 - Class Hand Width
Measurement of Hand Length in cm. / # of Males / # of Females / Total No. of Males and FemalesIn order to form a more accurate conclusion, the collection of additional data is necessary. The teacher has the option to include the data from all the classes running this experiment. Below find tables that will allow the tabulation of several classes of data.
Bar Graph the data from Tables 5 and 6, and then answer the questions that follow. Use the measurements of the width and length as your independent variable and the number of times that measurement appeared as your dependent variable.
Graph Title: ______
Observations/Analysis:
1. Examine the graphs. What is the shape of the graph for hand length? What is the most abundant measurement for hand length?
2. What is (are) the least abundant measurement(s)?
3. If we are to assign letters to represent the various lengths, what value(s) would we assign to the dominant genotype (HH)? The recessive genotype (hh)? The heterozygous genotype (Hh)?
4. What would be the phenotypic name for the (HH) genotype?
5. What would be the phenotypic name for the (Hh) genotype?
6. What would be the phenotypic name for the (hh) genotype?
7. What is the shape of the graph for hand width?
8. What is the most abundant measurement for hand width?
9. What is (are) the least abundant measurement(s)?
10. If we assign letters to represent the various widths, what value(s) would we assign to the dominant genotype (WW)? The recessive genotype (ww)? The heterozygous genotype (Ww)?
11. What would be the phenotypic name for the (WW) genotype?
12. What would be the phenotypic name for the (Ww) genotype?
13. What would be the phenotypic name for the (ww) genotype?
14. Are there any similarities in the graphs of the two characteristics? If so, what are they?
15. Are there any differences in the graphs of the two characteristics? If so, what are they?
16. Is there a difference in the length and width of the male and female hand? Does the gender of a person have an effect on the phenotype of a trait? Explain:
Conclusion:
Develop a written report that summarizes the results of this investigation. Use the analysis questions as a guide in developing your report. Make sure to give possible explanations for your findings by making connections to the NGSSS found at the beginning of this lab hand-out. Also, mention any recommendations for further study in this investigation.
The Genetics of Eye Color
The genetics of blood type is a relatively simple case of one locus Mendelian genetics—albeit with three alleles segregating instead of the usual two (Genetics of ABO Blood Types).
Eye color is more complicated because there's more than one locus that contributes to the color of your eyes. In this posting the description will entail the basic genetics of eye color based on two different loci. This is a standard explanation of eye color but, as we'll see later on, it doesn't explain the whole story. Let's just think of it as a convenient way to introduce the concept of independent segregation at two loci. Variation in eye color is only significant in people of European descent.
At one locus (site=gene) there are two different alleles segregating: the B allele confers brown eye color and the recessive b allele gives rise to blue eye color. At the other locus (gene) there are also two alleles: G for green or hazel eyes and g for lighter colored eyes.
The B allele will always make brown eyes regardless of what allele is present at the other locus. In other words, B is dominant over G. In order to have true blue eyes your genotype must be bbgg. If you are homozygous for the B alleles, your eyes will be darker than if you are heterozygous and if you are homozygous for the G allele, in the absence of B, then your eyes will be darker (more hazel) that if you have one one G allele.
Here's the Punnett Square matrix for a cross between two parents who are heterozygous at both alleles. This covers all the possibilities. In two-factor crosses we need to distinguish between the alleles at each locus so I've inserted a backslash (/) between the two genes to make the distinction clear. The alleles at each locus are on separate chromosomes so they segregate independently.
As with the ABO blood groups, the possibilities along the left-hand side and at the top represent the genotypes of sperm and eggs. Each of these gamete cells will carry a single copy of the Bb alleles on one chromosome and a single copy of the Gg alleles on another chromosome.
Since there are four possible genotypes at each locus, there are sixteen possible combinations of alleles at the two loci combined. All possibilities are equally probable. The tricky part is determining the phenotype (eye color) for each of the possibilities.
According to the standard explanation, the BBGG genotype will usually result in very dark brown eyes and the bbgg genotype will usually result in very blue-gray eyes. The combination bbGG will give rise to very green/hazel eyes. The exact color can vary so that sometimes bbGG individuals may have brown eyes and sometimes their eyes may look quite blue. (Again, this is according to the simple two-factor model.)
The relationship between genotype and phenotype is called penetrance. If the genotype always predicts the exact phenotpye then the penetrance is high. In the case of eye color we see incomplete penetrance because eye color can vary considerably for a given genotype. There are two main causes of incomplete penetrance; genetic and environmental. Both of them are playing a role in eye color. There are other genes that influence the phenotype and the final color also depends on the environment. (Eye color can change during your lifetime.)
One of the most puzzling aspects of eye color genetics is accounting for the birth of brown-eyed children to blue-eyed parents. This is a real phenomenon and not just a case of mistaken fatherhood. Based on the simple two-factor model, we can guess that the parents in this case are probably bbGg with a shift toward the lighter side of a light hazel eye color. The child is bbGG where the presence of two G alleles will confer a brown eye color under some circumstances.
Posted by Larry Moran at 11:30 AM
Labels: Biochemistry, Science Education
http://sandwalk.blogspot.com/2007/02/genetics-of-eye-color.html
Making Karyotypes
(Adapted from: Prentice Hall, Lab Manual A)
NGSSS:
SC.912.L.16.10 Evaluate the impact of biotechnology on the individual, society and the environment, including medical and ethical issues. AA
HE.912.C.1.4 Analyze how heredity and family history can impact personal health.
(Also addresses SC.912.L.14.6)
Background:
Several human genetic disorders are caused by extra, missing, or damaged chromosomes. In order to study these disorders, cells from a person are grown with a chemical that stops cell division at the metaphase stage. During metaphase, a chromosome exists as two chromatids attached at the centromere. The cells are stained to reveal banding patterns and placed on glass slides. The chromosomes are observed under the microscope, where they are counted, checked for abnormalities, and photographed. The photograph is then enlarged, and the images of the chromosomes are individually cut out. The chromosomes are identified and arranged in homologous pairs. The arrangement of homologous pairs is called a karyotype. In this investigation, you will use a sketch of chromosomes to make a karyotype. You will also examine the karyotype to determine the presence of any chromosomal abnormalities.
Problem Statement: Can chromosomal abnormalities be observed?
Safety: Be careful when handling scissors.
Vocabulary: centromere, chromosomes, chromatids, genes, homologous pairs, karyotype, mutations, Trisomy 21- Down syndrome, Klinefelter syndrome, Turner syndrome
Materials (per individual):
· Scissors
· Glue or transparent tape
Procedures:
Part A. Analyzing a Karyotype
1. Make a hypothesis based on the problem statement above.
2. Observe the normal human karyotype in Figure 1. Notice that the two sex chromosomes, pair number 23, do not look alike. They are different because this karyotype is of a male, and a male has an X and a Y chromosome.
3. Identify the centromere in each pair of chromosomes. The centromere is the area where each chromosome narrows.
4. Observe the karyotypes in Figures 4 and 5. Note the presence of any chromosomal abnormalities.
5. Comparing and Contrasting: Of the three karyotypes that you observed, which was normal? Which showed evidence of an extra chromosome? An absent chromosome?
6. Formulating Hypotheses: What chromosomal abnormality appears in the karyotype in Figure 4? Can you tell from which parent this abnormality originated? Explain your answer.
7. Inferring: Are chromosomal abnormalities such as the ones shown confined only to certain parts of the body? Explain your answer.
8. Using the incomplete chromosomal analysis provided by the lab, determine the probable identity of the mystery donor.
Incomplete Karyotype Analysis – provided by the Forensics Dept. Long Island, New York
Results/Conclusions:
1. Draw a data table in the space below in which to record your observations of the karyotypes shown in Figures 1, 4, and 5. Record any evidence of chromosomal abnormalities present in each karyotype. Record the genetic defect, if you know it, associated with each type of chromosomal abnormality present.