Download Chromosomes, Genes, and Alleles, oh my

Chromosomes, Genes, and Alleles, oh my!
In this activity, students will learn to relate the idea of the gene, genotype, allele,
and chromosome to the structure of DNA.
1. Draw a chromosome in its wound up version and then again in its
unwound form as chromatin.
2. Write a sequence of 20 bases to represent a gene. Write the
complementary strand for the gene.
Gene strand
Complementary
strand

The gene you just wrote could be part of the chromatin you drew in part 1
– it would occupy a small part of that chromosome. There would be
hundreds or thousands of other genes on that same chromosome.
3. This gene may have different alleles. Alleles are the different forms of a
certain gene – the different alleles all deal with the same trait but have
slightly different information. The different alleles of the gene will be
almost identical and will be in the same place on different chromosomes
but will have a slightly different base sequence in one or more locations.
 Use (and highlight) 2-3 base differences to write a different allele and
complementary strand for the gene you wrote.
Gene strand
Complementary
strand
4. The genetic information possessed by an individual makes up their
genotype. Most organisms (other than bacteria and every second
generation of plants) are diploid – they have paired chromosomes. Draw a
pair of chromosomes. The chromosomes in a pair are homologous,
meaning that they have information about the same genetic traits – the
genes for “nose shape” are in a certain location on these two
chromosomes. That means that we have two alleles for every trait.

We have 23 pairs of chromosomes. The two genes you wrote in
parts 2 and 3 could represent the two alleles an individual has.
5. When an organism has two different alleles for a certain trait, one of the
alleles may be dominant over the other. Only the more dominant allele of
the two is expressed in the person’s appearance or phenotype.
We can use symbols to represent the different alleles. If the allele for tall is
dominant over the allele for short, then we can call the allele for tall “T”
and the allele for short “t”.
 A tall person may have the genotype TT or Tt.
 TT is called homozygous dominant.
 Tt is called heterozygous.
 A short person does not have that tall allele. If they have the
recessive phenotype, then they must be double recessive or
homozygous recessive. They must have the genotype tt.
Illustrate these three genotypes and their phenotypes.