1. Terms you’ve gotta know
BASIC GENETICS TERMS
Terms you’ve gotta know

2. GENE Gene: a section of DNA that codes for a trait
A chromosome is a chunk of DNA and genes are parts of chromosomes

3. ALLELE Allele: the different options for a gene
Example: attached or unattached earlobes are the alleles for the gene for earlobe shape

4. DOMINANT/RECESSIVE
Dominant: an allele that blocks or hides a recessive allele
Recessive: an allele that is blocked by or hidden by a dominant allele
Question: Using purebred crosses, how did Mendel figure out that genes are either dominant or recessive?

5. HOMOZYGOUS/HETEROZYGOUS
Homozygous: When a person’s two alleles for a gene are the same
Heterozygous: When a person’s two alleles for a gene are different
You get one allele from your mom and one from your dad.
If you get the same alleles from your mom and dad, you are homozygous for that trait.
If your mom gave you a different allele than your dad, you are heterozygous for that trait

6. Tt GENOTYPE Genotype: A person’s set of alleles (gene options)
Genotype is written in letters
It is usually the first letter of the dominant allele to make it easier
Choose a letter for each of these traits. Write both the dominant and the recessive genotype allele letters
Attached Earlobes
Freckles
Dimples
Tongue-roller

7. GENOTYPE
Now, using your letters from before write a genotype for a person without freckles (Freckles are dominant)
Write a genotype for a person with freckles

8. GENOTYPE-HETEROZYGOUS AND HOMOZYGOUS
A Heterozygous genotype means an organism has both the dominant and the recessive allele (e.g. Aa)
Homozygous recessive means an organism has 2 recessive alleles (e.g. aa)
Homozygous dominant means an organism has 2 dominant alleles (e.g. AA)
Write a heterozygous genotype for handedness
Write a homozygous dominant and a homozygous recessive genotype for handedness

9. PHENOTYPE
Phenotype: A person’s physical features because of their genotype
What you look like (your phenotype) is based on what your genotype is (your genes)
What will the phenotype of these genotypes be:
WW, Ww, ww (Widow’s Peak dominant over straight hair line)
HH, Hh, hh (Hitch hiker’s thumb is dominant over a straight thumb)
CC, Cc, cc (Curly hair is dominant over straight hair)