1 Visible Genetic Traits in Humans Each student is to keep a record of the following traits, dominant or recessive, that...
Description
Visible Genetic Traits in Humans Each student is to keep a record of the following traits, dominant or recessive, that appear in his/her phenotype. Record this data on the blackboard or in a table by making an X in the appropriate column. For consistency, each trait has been assigned an arbitrary letter for representation.
The Traits:
A. Hold your hands before your face with the palm toward you. Place the two little fingers side by side and press them together. Do they run parallel their entire lengths or do the terminal digits flare out away from each other? Each bone in a finger is termed a phalanx; a flaring phalanx (B) is dominant over a straight phalanx (b). B. Dimples in the cheeks is a dominant trait. The dimples may be more than one per cheek or a dimple may appear in one cheek and not the other. Dimples (D) is dominant over no dimples (d). C. Darwin's Ear Point (E) is dominant over no ear point (e). D. Freckles (F) is dominant over no freckles (f). E. Free ear lobe (G) is dominant over attached ear lobe (g). F. Hairs on middle digits on back of fingers (H) is dominant over hairless middle digits (h). Examine your two middle fingers (the longest finger). G. Taster gene to PTC (J) is dominant over non-taster (j). H. Dark hair (M) is dominant over blonde or tawny hair (m). I. Examine the hairline on your forehead. A widow´s peak (P) is dominant over a straight or curved hairline on the forehead (p). J. The ability to roll the tongue into a longitudinal U-shaped trough (S) is dominant over the lack of this ability (s). K. Long eyelashes 3/8" or longer (T) is dominant over short eyelashes (t) less than 3/8" long. L. Tongue folding (V) is dominant over lack of this ability (v). To qualify as a tongue folder, you must be able to hold the tongue without bracing it against the teeth and fold the tip back sharply. This is an extremely rare trait. The chances are about 5 to 1 that you will not find this trait in your laboratory section. M. Lip Thickness: Thick lips are dominant (L) to thin lips (l). N. Thumb: The hitchhiker’s thumb (thumb tip bends backward more than 30 degrees) is dominant (B) to a straight thumb (b). O. Eye shape: Almond-shaped eyes are dominant (A) to round-shaped eyes (aa). P. Hair Texture: Curly hair is incompletely dominant (HH) to straight hair (SS). Those who have wavy hair are intermediate (HS).
(chart on board, for students to fill in) Trait Dominant Recessive % of class % of class description phenotypes phenotypes dominant recessive
Conclusions: 1. Total the numbers of the dominant phenotypes and recessive phenotypes in each trait for the whole class. Calculate the percentage of the class for each trait that has: a) the dominant phenotypes b) the recessive phenotypes (this job can be divided among the different members of the class to save time, and entered on the board). e.g. suppose 15 students had flaring phalanx (dominant) out of a class of 30, 15/30 x 100 = 50% of the class have the dominant phenotype. c) Is there any significant pattern to the percentage? If so, how can it be explained? 2. Total the number of factors for which you have a dominant phenotype and for which you have a recessive phenotype. a) What percentage of your 12 traits have the dominant phenotype? b) What percentage of your trait have the recessive phenotype? e.g. suppose 6 out of your 12 traits are of the dominant phenotype, 6/12 x 100 = 50% of your traits have the dominant phenotype. c) What explanation can you suggest for your results? 3. Compare your 12 traits with those of your laboratory partner. Calculate the percentage of agreement. Supposed you had 6 traits alike out of the 12 possible traits: 6/12 x 100 = 50% agreement. Contact as many class members as you can. Record all agreements. Compare traits with members of your family at home. Do your relatives have a higher percentage of agreement of phenotype with you than with any of your class members? Try to explain your findings.
