10.2 Mendelian Inheritance in Humans
NAME_______________________HR_____
BACKGROUND:
-Several human traits may be used to demonstrate Mendel’s Law of Segregation.
-These traits are controlled by a single gene with two alleles; each allele produces a distinct phenotype.
-Two alleles for each trait separate during meiosis.
OBJECTIVE:
-APPLY Mendel’s LAW of SEGREGATION
-DINSTINGUISH between genotype and phenotype
-INDENTIFY dominant and recessive traits
PROCEDURE:
1-IDENTIFY your PHENOTYPE for each of the following traits by hi-lighting the dominant or recessive allele
2-RECORD this information in the PHENOTYPE column.
3-DETERMINE your possible genotype(s)
4-RECORD your possible GENOTYPE(S) for each of the traits in the GENOTYPE column.
*Remember:
-if you have a recessive characteristic, you must have both recessive alleles
-if you have a dominant characteristic you may be either homozygous dominant or heterozygous.
-If you have a dominant phenotype, you may have no way to know if you carry a recessive allele.
-In this case, use a dash (-) to represent the unknown second gene.
DATA:
TRAITS
DIMPLED CHIN
NON-DIMPLED CHIN
FREE EARLOBE
ATTACHED EARLOBE
WIDOW’S PEAK
CONTINUOUS HAIRLINE
PTC TASTER
NON-TASTER
LEFT THUMB TOP
RIGHT THUMB TOP
BENT LITTLE FINGER
STRAIGHT LITTLE FINGER
NORMAL THUMB
HITCHHIKER THUMB
NO LONG PALMAR
LONG PALMAR
TONGUE ROLLER
NON-TONGUE ROLLER
RIGHT HANDEDNESS
LEFT HANDEDNESS
PHENOTYPE
CONCLUSION:
1. Which traits occurred most often?
2. Which do you think are better or more desirable?
EXPLAIN-
Possible GENOTYPE(S)
___ DOMINANT ___ RECESSIVE
___DOMINANT
___RECESSIVE
TRAITS:
Dimpled chin
-a cleft in the chin is a dominant trait
-D, dominant allele: dimple in chin
-d, recessive allele: absence of a dimple
Free ear lobe
-In most people, the ear lobes hang free
-E, dominant allele: free earlobes
-e, recessive allele: earlobes attached directly to the head
Widow’s peak
-hairline that forms a distinct point in the center of the forehead
-W, dominant allele: widow’s peak
-w, recessive allele: continuous hairline
Ability to taste PTC
-Some people detect a distinct bitter taste in small concentrations of the chemical phenylthiocarbamide (PTC), while others do not taste it.
-T, dominant allele: ability to taste this chemical
-t, recessive allele: are non-tasters.
**Place a PTC paper strip on your tongue and allow it to remain about 10 seconds.
-If you are a taster you will know it.
-If you have any doubt about your ability to taste the substance, you are a non-taster.
Interlocking fingers –
-When the fingers are interlocked, some people will almost invariably place the left thumb on top of the right
-F, dominant allele: left thumb on top of right
-f, recessive allele: right thumb on top of left
Bent little finger
-A dominant gene (B) causes the last joint of the little finger to bend inward toward the fourth finger
-B, dominant allele: bent little finger
-b, recessive allele for a straight finger
**Lay both hands flat on the table, relax your muscles, and note whether you have a bent of straight little finger.
Hitchhiker’s Thumb
-This characteristic, more precisely called distal hyper-extensibility of the thumb, can be determined by bending the distal joint of the thumb
back as far as possible. While there tends to be some degree of variation, certain individuals can bend it back until there is almost a 90degree angle between the two joints.
-H, dominant allele: no 90-degree bend in distal thumb joint
-h, recessive allele: 90-degree bend in distal thumb joint
Long palmar muscle
-A person homozygous for a recessive gene (l), has a long palmar muscle that can be detected by examination of the tendons running over
the inside of the wrists.
-L, dominant allele: only 2 tendons in both wrists (large middle one is missing)
-l, recessive allele: 3 tendons in one or both wrist
**Clench your fist tightly and flex your had. Now feel the tendons. If there are three, you have the long palmar muscle. If there are only
two tendons (the large middle one will be missing) you do not have this muscle. Examine both wrists – if you find this trait in one or both
wrists you have two recessive genes. If not, you have the dominant gene L.
Tongue Rolling
-Most individuals can roll their tongue into a U-shape when extending it from the mouth.
-T, dominant allele: cause the tongue to roll.
-t, recessive allele: a non-rolling tongue
Right-handedness
-Most individuals express a preference for using their right or left hand for tasks.
-H, dominant allele: right-handedness
-h, recessive allele: left-handedness
*A few individuals are ambidextrous and can use either or both hands interchangeably.