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Human Phenotypes and Genotypes

Number of Chromosomes : 22 autosomal + X + Y Number of base pairs: approximately 3 billion DNA base pairs Estimated number of genes: 20,000–25,000 genes.

We are all very close to being the same: Only about two base pairs in 1000 are different

Two of every type of chromosome. One from each parent. Two genes for every trait. One from each parent.

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 eye color: 2 brown Homozygous – having two genes of different types for a trait. eye color: one brown and one blue

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. Phenotype: Genotype:

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

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

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

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

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

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

8. Shape of the face. (Many different genes) Oval shape is dominant. Square shape is recessive Phenotype: Genotype: To show recessive traits the genotype has to homozygous. Homozygous means that both alleles for a trait are the same.

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

10. 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 Phenotype: Genotype:

11. 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 forms an angle with the closer segment is recessive and homozygous. Phenotype: Genotype:

12. 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. Phenotype: Genotype:

13. Eyelash Length Long eyelashes are dominant and homozygous or heterozygous. Short eyelashes are recessive and homozygous. Phenotype: Genotype:

14. 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 Phenotype: Genotype:

15. 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. Phenotype: Genotype:

16. Bent Little Finger In the dominant condition the center line 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. Phenotype: Genotype:

17. 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. Phenotype: Genotype:

18. 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. Phenotype: Genotype:

19. 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. Phenotype: Genotype:

20. 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. Phenotype: Genotype:

21. 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. Phenotype: Genotype: Clench the fist tightly and flex the hand. 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.

22. Size of Nose (works like incomplete dominance) Large is more than 38% of face length and homozygous. Medium is about 1/3 of face length and heterozygous. Small is less than 31% of face length and homozygous. Phenotype: Genotype:

23. Size of Ears (works like incomplete dominance) Large ears are 38% or more of the face length and homozygous. Medium sized ears are about 1/3 of the face length and heterozygous. Small ears are 31% or less of face length and homozygous. Phenotype: Genotype:

24. Width of Mouth (works like incomplete dominance) A wide mouth is 95% or more of interpupillary distance and is homozygous. A medium mouth is 70%-90% of interpupillary distance and is heterozygous. A small mouth is 65% or less of interpupillary distance and is homozygous. Try not to smile when being measured. Phenotype: Genotype:

25. Eye Size (Assume incomplete dominance) Large eyes (>30mm, corner to corner) are homozygous. Medium eyes (26-30mm, corner to corner) are heterozygous. Small eyes (<26mm, corner to corner) are homozygous. Phenotype: Genotype:

26. Reaction Time One student drops a ruler vertically between the thumb and finger of another student. The second student catches it. Best out of three drops. Record the drop in centimeters. Phenotype: Genotype:

27. Hand span Thumb to pinkie finger in centimeters. Phenotype: Genotype:

28. Blood Types A is dominant over O B is dominant over O A and B are co-dominant Phenotype: Genotype: