Notes: Human Genetics
You must read these notes carefully. We are skipping quite a bit of this lab, and you won’t know which
parts to do and which to skip without reading paying careful attention to what this says.
Here is some help getting started. First, a little glossary of terms:
Alleles are different forms of the same gene. We usually represent these alleles by symbols. The rule
about these symbols is that all alleles of the same gene must be represented by some version of the
same symbol.
Dominance (more correctly called “complete dominance) describes a relationship between two alleles in
which one of the alleles expresses itself over the other one. For example, the albino gene has two
alleles, A for normal pigmentation and a for albino pigmentation. A is completely dominant to a, so a
person who has both of these alleles (Aa) would only express the “A” trait—normal pigmentation. The
expressed trait is called the dominant and the hidden trait is called the recessive. By convention,
dominant traits are represented by capital letters and recessive traits by lower case letters.
A genotype is the actual alleles a person or other organism carries for a particular gene. For instance,
one genotype might be Aa (for the albino gene, this person carries one normal allele (A) and one albino
allele (a). This is also an example of a heterozygote—see below).
A phenotype is the actual expression of a trait in an individual. For example, our Aa individual in the
genotype definition would have a phenotype of “normal pigmentation” for this trait. Phenotypes are
the result of both genetic factors and environmental factors.
A homozygous individual has two identical alleles for a trait. For instance, most people are homozygous
A (or homozygous dominant) for the albino gene, meaning that they have the genotype AA. A person
who is albino would be homozygous for the recessive allele, or aa.
A heterozygous individual has two different alleles for a particular gene. For example, Aa. Since the A
allele is completely dominant to the a allele, this individual would have the normal pigmentation
phenotypic.
A monohybrid cross is a mating between two parents who are both heterozygous for one gene. For
instance, Aa x Aa would be a monohybrid cross.
We haven’t started doing genetics problems in class yet, so here’s the little example problem from the
beginning of the lab.
The mating is a monohybrid cross for a gene whose alleles are represented by the symbols H
(dominant) and h (recessive). Here’s the mating:
You can take it from here :^)
See the back for lab notes.
Notes for Human Genetics Lab.
You must read these notes carefully. We are skipping quite a bit of this lab, and you won’t know which
parts to do and which to skip without reading paying careful attention to what this says.
1.
Work in pairs for this lab. You will complete the following sections of the lab:
Part A, Part B, Section 1, and Part C. (Thus you will skip Part B, Sections 2 and 3, and Part D.)
Also, on the data sheets for Part C, Section 2, omit question 9. You are to do all the rest of
the questions Don’t skip questions 10-14, which actually come after the tables for question 9.
Of course, you will skip those parts of the data sheets which represent the parts of the lab
you are skipping.
2.
For Part C question 14, you will need class totals for boys and girls. There will be a table
created on the board for you to record the genders of your children.
3.
Follow instructions precisely, and you should have no problems.