Human Traits & Mode of Inheritance Lab Report

HUMAN TRAI S EXERCISE

INTRODUCTION

Analyses of human traits offer genetic examples including complete dominance. incomplete dominance, codominance, and sex linkage. In this exercise you will examine the complexities and modes of inheritance of many human genetic traits.

Monogenetic characteristics

Analysis of human genetic characters is usually complex because many characters are influenced by multigene interactions and environmental factors. In this exercise we will concentrate on those characteristics determined by variations of a single gene without much environmental influence. Y bu should be able to determine the phenotype and make good inferences (if not precise) about the genotypes controlling the characteristic. This will be particularly important when you analyze dominant phenotypes because you will not know by certain whether the second allele is also dominant or recessi ve for that particular characteristic under study. Some of these characteristics are discussed below:

Ability to taste Phenylthiocarbamide (PTC)

Determined by a dominant allele T that seems to confer the ability to taste the chemical.

Homozygous recessives for the allele lack the ability to taste PFC. In order to asses your tasting abilities, place a piece of control paper on your tongue and keep it there for at least 10 seconds. Then. place a piece of paper in your mouth and keep it for 10 seconds. A distinct bitter taste will develop during this time if you are a taster. If you have to wonder if you taste or not, then you are a nontaster.

Ability to roll tongue

This characteristic is determined by a dominant gene R, that gives some people the ability to roll the tongue into a characteristic U shape.

Earlobes

Attached earlobes represent the homozygous recessive condition (gene f).

Interlocking fingers

Studies suggest that placing the left finger over the right when you cross your hand is due to a dominant gene L.

Bent little finger

Caused by a dominant gene B that causes the last joint of the little finger to bend inward toward the fourth finger. Lay your hands flat on the bench while relaxing the muscles to observe this phenotype.

Widow’s Peak

Due to a dominant gene W, this shows in some people as a drop in the hairline downward forming a distinct point at the center of the forehead. Examine your front hairline to determine if you have this phenotype.

Hitchhiker’s thumb (distal hyperextensibility of the thumb)

The expression of this trait is due to a recessive gene T with variable expressivity (only one thumb) with 5% reduction in penetrance.

Long palmar muscle

Homozygocity for the I gene determines the presence of long palmar muscle. This is detected by examining the tendons that run over the inside of the wrists. Close your fist tightly and flex your hand. If there are three tendons running into the wrist, you have the long palmar muscle.

Otherwise, if you see two tendons with the large middle one will be missing. then you do not have the muscle.

Mid digital hair

Presence of hair on the second (middle) joint of one or more fingers is due to a dominant allele M.

word image 2964 The following chart shows the inheritance pattern of a number of known traits in human beings that are single locus traits. Underline your phenotype and possible genotype for each trait. Then word image 2965 circle the phenotype that is the most frequent in the population (your class).

PHENOTYPE

Trait Dominant Recessive Possible Genotype

word image 2966 word image 2967 vrc tasting

Taster

Nontaster

word image 2968 Tt tt

2. Tongue rolling

Roller

Nonroller

word image 2969 Rr rr

3. Ea bes

Free

Attached

word image 2970 ff

4. Sw at Glands (sex-linked recessive)

Present

Absent

SS Sa aa s_

5. Rh Factor

Rh+

 

Rh+Rh+ Rh+rh-

rh-rh-

6. Blood Type

A, B. AB

o

AA. AO, BB, BO,

word image 2971 AB, 00

  1. Hair Color Dark Light word image 2972 HH Hh hh

9. Dexterity

Right-handed

L*ft-handed

RR RI word image 2973 word image 2974

10. Interlocking Fingers

Left over Right

Right over Left

LL Lr rr

I I. Bent Little Finger

Bent

Straight

word image 2975 word image 2976 Bb bb

12. Double joints in Fingers

Present

Absent

word image 2977 dd

13. Albinism

Normal

Albino

word image 2978 word image 2979 Na aa

14. Widow’s Peak

Present

Absent

 

15. Curly Hair (incomplete dominance)

Curly, Wavy

Straight

cc cs word image 2980 word image 2981

16. Dimples

Present

Absent

word image 2982 Dd dd

17. Nose Shape

Roman

Straight

ee

18. Freckles

Present

Absent

word image 2983 ff

19. Hitchhiker’s thumb

Present

Absent

 

20. Color Blindness (sexlinked recessive)

Normal word image 2984

Color Blind

cc Cc cc

  1. word image 2985 Hair Color Nonred Red word image 2986 Nn nn

PHENOTYPE

Trait

Dominant

Recessive

Possible Genot

e

21. Long Palmar Muscle

Absent word image 2987

Present

   

22. Mid Digital Hair

Present

Absent

Pvtvl

Mm

mm

23. White Forelock (sexlinked recessive)

Present

Absent

word image 2988

Ff

ff

24. Vision

Nearsighted

Normal

NN

Nn

nn

25. Vision

Farsighted

Normal

FF

word image 2989

ff

26: Vision

Astigrnatism

Normal

AA

An

nn

27. Headaches

Migraine

No Migraine word image 2990

MEI

Mm

mm

28. Eyelashes

Long

Short

word image 2991

LS

word image 2992

29. Fingers

Polydactylous

Normal

PP

Pn

nn

30. Fingers

Brachydactylous

Normal

BB

Bb

bb

31. Toes

Webbed

Normal

ww

Wn

nn

32. Inny-Outy Navel

Inny

Outty

11

10

00

Now, construct a pedigree of-your family that analyzes the inheritance of one of the traits shown in the previous table. Your pedigree should include your grandparents and their brothers and sisters in the first generation; your parents and their brothers and sisters in the second generation. and you and your brothers. sisters, and cousins in the third generation. Then, analyze your family pedigree and determine the mode of inheritance of the trait you selected.

Human Trait Analyzed

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