Download LAB: Inheritance of Human Traits

INHERITANCE OF HUMAN TRAITS
Heredity can be described as the passing on of traits or characteristics from parent to offspring through
chromosomes. A gene is a section on a chromosome that contains genetic information for a single trait. Since
genes are randomly distributed into gametes by the process of meiosis, it is not possible to accurately predict the
appearance of all traits in offspring. However, it is possible to calculate the probability of an offspring inheriting
a single trait.
Information contained in genes cannot be seen, therefore, symbols are used to represent the genetic
information. A dominant gene hides the appearance of a recessive gene. Dominant traits are represented by
a capital letter. Recessive genes are present on the chromosome but the traits are not visible in the organism.
Recessive genes are represented by a lower case letter. In order for a recessive trait to be displayed, both
alleles for the trait must be recessive. Alleles are different forms of a gene. Some characteristics are neither
dominant nor recessive and a blending of traits occurs. The blending of traits is called incomplete dominance.
The sex of an organism is determined by the sex chromosomes inherited from the parents. An individual
that has two X chromosomes is a female. An individual with an X and a Y chromosome is a male. Since each
parent donates one chromosome to every offspring, genes occur in pairs.
Critical Terms:
1. Genotype = The genetic make-up of an organism that is represented by letters
i.e. BB represents the information contained in the gene
2. Phenotype = The trait seen in an organism
i.e. Brown hair
3. Homozygous = Individual who has inherited only dominant or recessive alleles for a trait
i.e. BB or bb
4. Heterozygous = An individual the contain a dominant and recessive allele for a trait.
i.e. Bb
Procedure:
1. Decide which individual in the group will represent the female and the male for each combination of
traits.
2. The male should toss the penny on top of the desk. If the coin lands heads up, the offspring is
female. If the penny is tails up, the offspring is male. Record your data in the chart.
3. Two pennies should be tossed for the remainder of the traits on the chart. One toss from mom and
one from dad.
4. Heads represents donation of the dominant allele and tails represents donation of the recessive allele.
5. Fill in the chart for each trait according to the coin tosses.
6. Draw a picture of your fictitious baby and answer all questions.
Hereditary Traits Key
Traits
Shape of face
Cleft in Chin
Size of Ears
Size of Nose
Dimples
Shape of Lips
Size of Mouth
Length of Eyelashes
Shape of Eyebrows
Position of Eyebrows
Size of Eyes
Position of Eyes
Spacing of Eyes
Shape of Eyes
Freckles
Hair Type
Widow’s Peak
Dominant
(2 Heads)
RR
Round
CC
Absent
LL
Large
LL
Large
DD
Present
TT
Thick
LL
Large
LL
Long
BB
Bushy
NN
Not Connected
LL
Large
SS
Straight
EE
Close Together
AA
Almond
FF
Present
HH
Curly
WW
Present
Hybrid
(One head, One tail)
Rr
Round
Cc
Absent
Ll
Normal
Ll
Medium
Dd
Present
Tt
Normal
Ll
Medium
Ll
Long
Bb
Bushy
Nn
Not Connected
Ll
Medium
Ss
Straight
Ee
Normal
Aa
Almond
Ff
Present
Hh
Wavy
Ww
Present
Recessive
(2 Tails)
rr
Square
cc
Present
ll
Small
ll
Small
dd
Absent
tt
Thin
ll
Small
ll
Short
bb
Fine
nn
Connected
ll
Small
ss
Slanted Upward
ee
Far Apart
aa
Round
ff
Absent
hh
Straight
ww
Absent
DATA
Offspring Results
Traits
Sex
Coin Toss
(HH, HT, or TT)
H_
Genotype
(i.e. RR)
X_
Homozygous or
Heterozygous
Phenotype
(i.e. Round)
Shape of Face
Cleft in Chin
Size of Ears
Size of Nose
Dimples
Shape of Lips
Size of Mouth
Length of Eyelashes
Shape of Eyebrows
Position of Eyebrows
Size of Eyes
Position of Eyes
Spacing of Eyes
Shape of Eyes
Freckles
Hair Type
Widow’s Peak
*** DRAW A PICTURE OF YOUR OFFSPRING ON A SEPARATE SHEET OF PAPER***
ANALYSIS
1. What chance did you and your partner have of producing a female offspring? A male offspring? Express your
answer as a percentage.
2. Based on the observation of other offspring, were there any offspring with identical traits to your offspring?
Explain why this might or might not occur.
3. If a male that is homozygous for widow’s peak (WW) reproduces with a female who is heterozygous for
widow’s peak (Ww), what are all of the possible genotypes and phenotypes of their children?
4. If a child has straight hair, what are the possible genotypes of it parents?
5. Explain how it is possible for an offspring to have a trait that is not seen in either of the parents. (i.e., almond
eyed parents producing offspring with round eyes)
6. Which traits in this investigation show incomplete dominance? (Reread the opening paragraph)
7. Is it possible to have some genetic traits that were seen in your grandparent but not your parents? Explain.
8. There is a small isolated village in Spain where a large number of people are polydactyl. Polydactyl means
having extra fingers or toes. Why does this trait tend to be passed on from generation to generation?
9. Explain how geographic isolation, such as that seen in Spain, can be harmful to the health of an entire
species.
10. In some cultures, females can be divorced for not producing male offspring. Based on your knowledge of
genetics, explain why this is wrong. Remember who tossed the coin to determine the sex of your offspring.
11. Using Mendel’s Laws, explain why the genotype of any one coin toss does not depend upon the results of
another.
CONCLUSION
The probability of inheriting any given trait is the product of each of the individual probabilities. For example,
the probability of having a female offspring is ½ and the probability of having an offspring with a cleft in their
chin is ¼. Therefore, the probability of having a female child with a cleft chin is 1/8 (½ X ¼).
1. What is the probability of inheriting a round face?
2. What is the probability of inheriting a square face?
3. What is the probability of inheriting a large nose?
4. What is the probability of having a child with a square head and a large nose?
5. What is the probability of having a female child with a square head and a large nose?