1. Genetics
Unit 6

2. Heredity
Gene
A sequence of nucleotides that code for a specific trait
Ex: eye color, blood type
Allele
Two or more different versions of a gene (trait)
Ex: wet earwax versus dry earwax

3. Simple (Mendelian) Genetics
Dominant Alleles (represented by capital letters)
Recessive alleles (represented by lower case letters)
Genotypes
Homozygous dominant: BB
Homozygous recessive: bb
Heterozygous: Bb
Phenotypes
Either the Dominant or recessive

4. Complex Heredity Incomplete Dominance How can you tell?
When the dominant allele is unable to completely mask/hide the recessive allele…so we get a blend of the two alleles
How can you tell?
When two homozygous individuals have a third different phenotype
When the heterozygous is a blend of the homo dom and homo rec

5. Complex Heredity Codominance How can I tell?
When there are two alleles that are BOTH dominant
End up with BOTH versions of that gene present (like a roan horse or a cow!)
How can I tell?
When you see BOTH alleles present, NOT blended…but both present!

6. Complex Heredity Multiple Alleles How can you tell?
When there are more than two different versions for a gene
Ex: blood type
How can you tell?
More than one letter

7. Complex Genetics Sex-linked How can I tell?
When the gene is located on the X chromosome (the 23rd pair in humans)… the chromosome that determines sex.
How can I tell?
Always written with an X and a superscript (like this: XAXa)
More males affected than females
EX: calico cats, red-green colorblindness

8. Complex Genetics Polygenic How do I tell? Multiple GENES involved
Phenotypes are in a range
Ex: skin color, height