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What could you change in your experiment to increase your confidence in your results?


Instructor: Section:

Human Genetics Lab Basic Mendelian genetics is inheritance of biological features that are controlled by a single locus (the specific location of a gene); therefore, in basic Mendelian genetics, the phenotype (physical trait) of an individual is controlled by a single genotype (gene that it carries). Most traits are not simple Mendelian (they are affected by multiple loci and the environment as well). Mendelian traits in humans include sickle-cell anemia, Tay-Sachs disease, Huntington’s disease, and cystic fibrosis. Today, you will be investigating your own phenotypes and possible genotypes and examining the relationship between genotype and phenotype for simple single-locus Mendelian genetics.

Why are we doing this lab? l. To introduce you to basic Mendelian genetics. 2. To examine the relationship between your own phenotype and genotype.

Part I: Use the pictures and following instructions to fiIl out the table on the next page about yourself.

Picture I – Tongue rolling is the dominant phenotype. The inability to roll your tongue is recessive.

Picture,B – Having a widow’s peak (your hairline comes to a point in the center of your forehead) is the dominant phenotype. No widows peak (a shaight hairline) is recessive.

Picture C – A detached earlobe is the dominant phenotype. Attached earlobes are recessive.

Picture D -Hitchhiker’s thumb (being able to bend your thumb joint backwards) is the dominant phenotype. No hitchhiker’s thumb (thumb can only bend back until it is straight) is recessive.

Picture E -Bent little finger (the top joint of your little finger is bent towards your ring finger) is the dominant phenotype. A straight little finger is recessive.

Picture F- Having any kair on your mid-digit (the middle section of your finger; between the section with your nail and the section where you wear a ring) is the dorninant phenotype. No mid-digital hair is recessive.

Picture G -Having dimples (of any size on one or both sides) is the dominant phenotype. Ng dimples is recessive.

Picture 11- Short hallux (your hallux/big toe is shorter than your second toe) is the dominant phenotype. Long hallux (your hallux/big toe is longer than your second toe) is recessive.

Picture /- Short index finger means that your index finger is shorter than your ring finger. This may be a sex-influenced trait. In males short index finger is the dominant phenotype. In females long index finger is the dominant phenotype. This means that the possible genotypes for “short fi.nger” will be different depending on your gender.

Taste papers. There are four types of paper, including the control. To taste a paper tear one small rectangle out of the booklet and set it on your tongue. You may taste a control paper first so that you know what the paper tastes like. If you can tell any difference between the control and one of the test papers, you are a taster and have the dominant phenotype for that chernical. ln all cases tasting the chemical is dominant and non-tasting is recessive.

CBIOlOl Lab: Human Genetics p. t/6

Table for several body trai1. Your phenotype and possible or several body tratts.

Body Trait Dominant

Allele Recessive

A11ele Your Phenotype

All your possible genotypes

Tongue R r (. ot R.Y. Forehead w w N W ord yV.l Earlobe E e

Thumb Hi hi ,r hl Little Finger Bf bf tf ,{ Mid-Digit H h

Cheeks D d (,i; r: Hallux Ha ha

Index Finger Male: S” Female: SL

Male: SL Female: Ss

PTC taster P p r( Benzoate taster B b ( -.n,,

‘V’t Thiourea taster T t T* “[+

Table 2. Class data for relative difference in length of index and ring fingers (mm) for males vs females.

Indexfinger length is a continuotts trait. Measure the length of your index and ringfingers using a ruler in mm

and calcilate the dffirence (index – ring; note: vulues cun be negative!)- You will be investigating whether relative dffirence infinger length dffirs for males vs females.

Me: Length of index finger: Length of ring finger: Index – ring: Fill in the following table with the class data and use it as the basis for your work in part IV.

Males Females

–/ L1

f J vnrn C-) o

.1 *L-

CBIOlOl Lab: Human Genetics p.216

who cannot.


-, i’ ,

\ , t r-{‘rPart II: Answer the questions using the information in Table 1 about these traits.

L For this set of questions, consider a man who can taste PTC and a woman

a. Do we know for sure what the genotype of the man is?

c. If the man

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di*rpe: ,f J*t*\,r€4″^, S.6 i S .>1. 5o /, clatrn€ (, te-t fl , ‘r ‘t’*,ca.,J ,6. ‘,$ *

b. Do we know for sure what the genotype of the woman is? _+_ is homozygogs, what percent of the time will their kids be able to taste PTC?.,;, :;

d. If the rnan is heterozygous, what of the time will their kids be able to taste PTC?

9o’/. , +_’


e. If the couple has a child who cannot taste PTC, what did we leam about the father?

2. You have dimples and your spollse does not. Could you have a child with dirnples? Why?


3. You and your father have rnid-digital hair. Your mother and your spouse do not. What is the probability that your first child will have rnid-digital hair?

4. You and your spouse both have attach.d ;;A;;;lMhat percent of your kids will have attached earlobes? eP

5. You have a short hallux. What, if anything, do we know about your parents?


** 3 ctr,i’ J

CBIOlOl Lab: Human Genetics p.316

PART III: Answer the following questions about the frequency of alleles in a population. 6. Imagine a population in which 100 individuals were EE, 100 individuals were Ee, and 100 individuals

were ee. What percentage of the alleles in this population are recessive (little e)?

^ ‘,/ .ti

7. Now imagine that there were wolves that could catch individuals by their detached earlobes and these wolves ate 100 individuals (Note that both EE and Ee individuals can both be caught by the wolves

because they have the same phenotype.) Now the population contains 50 EE individuals, 50 Ee individuals, and 100 ee individuals. Now what percentage of the alleles in this population are recessive (little e)?

8. Now imagine a population (with individuals of all possible genotypes) whose food supply is sometimes contaminated with a poison that tastes like benzoate (Note that benzoate itself is NOT toxic). Everyone who can taste benzoate notices the food is contaminated, stops eating and lives. However, everyone J, who cannot taste benzoate eats the food and dies. The survivors (the benzoate tasters) reproduce. Will there be anyone in this new generation that CANNOT taste benzoate?

a. Why?

CBIOlOl Lab: Human Genetics p.4/6

q:_I i ”

Part IV: Answer the questions based on the data for the difference in finger length in Table 2. You will be investigating whether relative finger length differs for males vs females.

9. Setup your hypotheses: H:


10. Calculate the mean, standard deviation, and t-Test p-value for difference in relative finger length for males vs females. Use the function :T.Test(arrayl, array2, 2, 2) – note the last # is a 2!es. Use the function :T.Test(arrayl, array2, 2, 2) – note

Males Females




1 1, Do you reject or fail to reject the null hypothesis?

12. Write a results sentence (include all relevant parts; see previous problems and pp. 4-5 rn the stats notes):

13. Draw a bar graph comparing the means and standard deviations of both sexes and label axes:

CBIOlOl Lab: Human Genetics p.5/6

14. Make conclusions about your results. Do you think this is a simple dominance trait in which you could

link relative length directly to LL, Ll, and ll (could you make a Punneff square for inheritance)? Why or why not?

i5. Make conclusions about your results. Do you think this is a sex-linked trait? Why or why not?

16. Do you think most traits are like this? Why or why not?

17. What could you change in your experiment to increase your confidence in your results?

18. Are your data truth? Is your theory? Explain how your experiment looking at finger length relates to truth.

CBIOlOl Lab: Human Genetics p.616

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