Homework 2

Complete this worksheet to learn about your own genotype. Follow the directions listed at the top of the page.

NAME:___________________________________________

Human Phenotypes and Genotypes Worksheet: Test yourself!

Genotypes:

People can have two genes of the same type for a trait, or two genes of different types for a trait.

· Heterozygous – having two genes of the same type for a trait (Example: eye color: 2 brown)

· Homozygous – having two genes of different types for a trait (Eye color: one brown and one blue)

· Traits can be dominant or recessive. Recessive traits take precedence in the phenotype in heterozygous pairs.

DIRECTIONS:

Answer the questions below based on what you know about genetic inheritance.

1. For each question, examine your traits (phenotype) for each category. (you may need to use a mirror, or ask someone for help.

2. Determine if your genotype for that trait is homozygous dominant (AA), heterozygous (Aa) or homozygous recessive (aa) for each trait. Use the directions below to help determine this. You may also use what you know about family member’s traits to help you determine if you are homo- or heterozygous for a trait.

· Phenotype = What is the version of the trait you have?

· Example: you have blue eyes

· Genotype = what does that tell you about your genotype for that trait?

· Example: Blue eyes means you must have 2 recessive forms of the gene, making you homozygous recessive—“aa”).

· If you are unsure about your genotype because you possess the dominant trait (i.e., you’re not sure if you’re AA or Aa), try to guess based on what you know about the presence of the trait in your family. Do many (or all) of your relatives possess the trait?

· Rule of thumb: if everyone in your family possesses a trait, its likely you are AA, but if some do and others don’t, you’re likely Aa.

· If you have absolutely no idea, assume heterozygous.

EXAMPLE. Cleft in the Chin: Absence of a cleft is dominant and may be either homozygous or heterozygous. The presence of a cleft is recessive and represents a homozygous condition.

1. Cleft in the Chin: Absence of a cleft is dominant and may be either homozygous or heterozygous. The presence of a cleft is recessive and represents a homozygous condition.

2. Hair Curl: Curliness of hair works like incomplete dominance… Curly is homozygous. Wavy is heterozygous. Straight is homozygous.

3. Hairline: A widow’s peak is dominant and may be either homozygous or heterozygous. A straight hairline is recessive and homozygous.

4. Dimples: Dimples are dominant and homozygous or heterozygous. Absence of dimples is recessive and homozygous.

5. Earlobes: Definite free earlobes are dominant and homozygous or heterozygous. Attached earlobes are recessive and homozygous.

6. Freckles on Cheeks: Freckles are dominant and homozygous or heterozygous. Lack of freckles is recessive and homozygous.

7. Nose: Roman – A nose with a bump is dominant. Straight – A nose without a bump is recessive.

8. Eye Color (Two or more genes): 1st Gene (if brown can mask second gene): Brown is dominant over all. Blue is recessive. 2nd Gene: Green is dominant. Blue is recessive.

9. Hair Color (Two or more genes): 1st Gene (if black can mask other genes): Dark is dominant. Less Dark is recessive. 2nd Gene: Red is dominant. Blond is recessive.

10. Hitch-hiker’s Thumb: A thumb that is straight when fully bent back is dominant and is either homozygous or heterozygous. A thumb in which the segment furthest from the hand curves backward, is recessive and homozygous.

11. Mid-digital Hair: The presence of hair on the back of the middle joint of the fingers is dominant and is either homozygous or heterozygous. The absence of hair on the back of the middle joint of the fingers is recessive and homozygous. You will need to look carefully as the hair can be very fine, particularly in women.

12. Eyelash Length: Long eyelashes are dominant and homozygous or heterozygous. Short eyelashes are recessive and homozygous.

13. Tongue Rolling: The ability to roll the tongue, side edges up, is a dominant trait and is either homozygous or heterozygous. The inability to roll the tongue is recessive and homozygous.

14. Tongue Folding: The ability to fold the tip of the tongue backwards, without touching the roof of the mouth, is recessive and homozygous. The inability to fold the tongue as described is dominant and is either homozygous or heterozygous.

15. Bent Little Finger: In the dominant condition the centerline of the end segment of the little finger bends slightly towards the ring finger. It is either homozygous or heterozygous. A perfectly straight little finger is recessive and homozygous.

16. Interlaced Fingers: Fold your hands together, interlacing the fingers. Now look at your thumbs. Left over right is dominant and either homozygous or heterozygous. Right thumb over left is recessive and homozygous.

17. Index Finger Length: The trait for a short index finger is a sex-influenced characteristic, which means, in this case, that it is dominant in males and recessive in females. The gene for long index finger is dominant in females.

18. Big Toe Length: The dominant trait is a big toe that is shorter in comparison to the 2nd toe. When the big toe is longer than the 2nd toe, this is a manifestation of the homozygous recessive.

19. Hair on the Back of the Hand: Hair on the back of the hand is dominant and either homozygous or heterozygous. Hairless hands are recessive and homozygous.

20. Number of the Palmar Tendons: Two tendons in both wrists is dominant. It is either homozygous or heterozygous. The appearance of a third tendon, even in just one wrist, is recessive and homozygous. (To test: Clench your fist tightly and flex the hand back. Feel the tendons in the wrist. You should be able to distinguish two, perhaps even three. Do this for both wrists. One wrist might have two tendons, the other three.)

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Your phenotype ____no clift chin____

Your genotype__AA__(could be Aa or AA; best guess is AA, b/c none in family)__

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