Human Inheritance

Human Inheritance

Name: ______Date: ______

Background:

Using the laws of heredity and probability, biologists have learned about the genetics of many human traits. In these traits, several pairs of genes are involved and the pattern of inheritance is complex.

For this activity we will assume that only one pair of genes, one gene from the father and one from the mother regulate the traits we are studying. Knowledge of your own traits and genetic makeup can give you information about the genetic makeup of your parents, and perhaps your brothers and sisters.

Objectives:

In this activity you will:

1)Determine your phenotype for several traits.

2)Determine (as far as possible) your genotype for the same traits.

Procedures and Observations:

Part 1. Your phenotype and genotype for some common traits.

You will determine your phenotype (your physical traits) and try to determine your genotype (the genes that give you those physical traits) for the traits listed in Table 1.

If your traits are the dominant traits, you cannot be sure right now if you carry the recessive gene. In this case, enter the capital letter and a blank for your genotype. If you have the recessive gene, your genotype must be both recessive genes.

1)Have your partner check your earlobes.

Free earlobes are dominant. If you have free earlobes, enter L_ into the chart on page 3. People with earlobes attached directly to the side of their head have the recessive gene. They should enter ll. into the chart.

2)Check your eye color.

Only people having the recessive genotype have blue eyes. If you have blue eyes, enter bb into the chart. People who have the dominant gene may have different shades of brown, hazel or green eyes. If you do, enter B_ for your genotype.

3)Have your partner check your hairline.

A widow’s peak is a hairline that forms a downward point in the middle of the forehead. This is caused by the dominant genotype W_. A smooth hairline is caused by the recessive genotype ww.

4)Check to see if you can roll your tongue.

A dominant gene, R, gives some people the ability to roll their tongues into a “U” shape when it is extended. People with the recessive genes, rr, cannot roll their tongues.

5)Check to see if you can fold your tongue.

A dominant gene, T, gives some people the ability to fold their tongues over. People with the recessive genotype tt cannot.

6)Look at your little fingers.

Place your hands on a flat surface, palms down and relax. Check to see if the first joints of your little fingers are bent inward or are straight. If they are bent, the dominant gene F has caused this. Straight little fingers are a result of the recessive genotype, ff.

7)Check to see if you have hair between the middle joint and the top joint of your fingers.

Individuals who have hair on the middle joints of their fingers have at least one dominant gene, H. Those with two recessive genes, hh, do not have hair in that area.

8)Check your hair color.

Individuals with red hair have the recessive gene nn. Individuals with any other hair color have at least one dominant gene, N.

9)Check your hair type.

People who have curly hair have at least one dominant gene, C. People with straight hair have the recessive genotype cc.

10)Have your partner check your eyelashes.

Long eyelashes are the result of the dominant gene S. Short eyelashes are the result of the recessive genotype ss.

11)Do you have more than 5 fingers on your hands?

Some individuals are born with the dominant gene P that causes them to have more than 5 fingers on each hand. If you have only five fingers, you have the recessive pp.

Traits and symbols for genes / Phenotype
(Physical traits) / Genotype
(Genes causing the physical traits)
Shape of the earlobe
L_ or ll
Eye color
B_ or bb
Shape of hairline
W_ or ww
Ability to roll tongue
R_ or rr
Ability to fold tongue
T_ or tt
Shape of little finger
F_ or ff
Hair on middle joint of fingers
H_ or hh
Hair color
N_ or nn
Curliness of hair
C_ or cc
Eyelash length
S_ or ss
Number of fingers
P_ or pp

Now record the data for your entire class. Let’s also look at whether males or females are more likely to have these traits.

Record how many males have each of the dominant traits, and how many have the recessive traits. Do the same for females.

Traits and symbols for genes / Male Dominant / Male Recessive / Female Dominant / Female
Recessive
Shape of the earlobe
L_ or ll
Eye color
B_ or bb
Shape of hairline
W_ or ww
Ability to roll tongue
R_ or rr
Ability to fold tongue
T_ or tt
Shape of little finger
F_ or ff
Hair on middle joint of fingers
H_ or hh
Hair color
N_ or nn
Curliness of hair
C_ or cc
Eyelash length
S_ or ss
Number of fingers
P_ or pp
11
10
9
8
7
6
5
4
3
2
1
M.D. earlobe / M.R. earlobe / F.D. earlobe / F.R. earlobe / M.D roll tongue / M.R. roll tongue / F.D. roll tongue / F.R. roll tongue / M.D. finger mid-hair / M.R. finger mid-hair / F.D. finger mid-hair / F.R. finger mid-hair / M.D. long eyelash / M.R. long eyelash / F.D. long eyelash / F.R. long eyelash

1)Does it appear that any of the traits are sex-linked (show up only in males or females)?______

2)Think about others in your family – parents, brother, sisters, etc. Do you see the same traits in them that you see in yourself? ______

3)If having more than 5 fingers is dominant, why don’t more people have more than 5 fingers? ______