human genetics 2
,you will be investigating your own phenotypes and possible genotypes and examining the relationship between genotype and phenotype for simple single-locus Mendelian genetics. Since we have not covered genetics in detail, we will begin from a broad standpoint today, and next week focus on molecular biology, and discuss genetics from a gene expression standpoint.
Why are we doing this lab?
- To introduce you to basic Mendelian genetics.
- To examine the relationship between your own phenotype and genotype.
Part I: Use the pictures and following instructions to fill out the table on the next page about yourself.
Picture A – 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 straight 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 hair 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 dominant phenotype. No mid-digital hair is recessive.
Picture G – Having dimples (of any size on one or both sides) is the dominant phenotype. No dimples is recessive.
Picture H – 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 I – 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 finger†will be different depending on your gender.
Table 1. Fill in your phenotype and possible genotypes for several body traits. For example,
- If you can roll your tongue: Your phenotype = “roll tongue†& All your possible genotypes = “RR or Rrâ€
- If you can’t roll your tongue: Your phenotype = “can’t roll tongue†& All your possible genotypes = “rrâ€
|
Body Trait |
Dominant Allele |
Recessive Allele |
Your Phenotype |
All your possible genotypes |
|
Tongue |
R |
r |
||
|
Forehead |
W |
w |
||
|
Earlobe |
E |
e |
||
|
Thumb |
Hi |
hi |
||
|
Little Finger |
Bf |
bf |
||
|
Mid-Digit |
H |
h |
||
|
Cheeks |
D |
d |
||
|
Hallux |
Ha |
ha |
||
|
Index Finger |
Male: SS Female: SL |
Male: SL Female: SS |
Part II: Answer the questions using the information from the first page about these traits.
- For this set of questions, consider a man who can roll his tongue and a woman who can’t.
- Do we know for sure what the genotype of the man is? _________
- Do we know for sure what the genotype of the woman is? _________
- If the man is homozygous, what percent of the time will their kids be able to roll their tongues?
- If the man is heterozygous, what percent of the time will their kids be able to roll their tongues?
- If the couple has a child who cannot roll their tongue, what did we learn about the father?
- You have dimples and your spouse does not. Could you have a child with dimples? Why?
- You and your father have mid-digital hair. Your mother and your spouse do not. What is the probability that your first child will have mid-digital hair?
- You and your spouse both have attached earlobes. What percent of your kids will have attached earlobes?
- You have a short hallux. What, if anything, do we know about your parents?
