A Common Language & Rules
Gene
A segment of DNA that carries
hereditary instructions and is passed
from parent to offspring.
 Genes are located on the
chromosomes.
 Example: height, flower color, shape of
eyes, hair texture,…

Allele


A version of a single
gene.
Example:
 1) Gene: Height
Allele: short, tall
 2) Gene: Flower Color
Allele: purple, white
3) Gene: Hair Texture
Allele: ?
Dominant
The “stronger” allele. A dominant allele
or trait will “cover” a recessive allele or
trait.
Go to #9 on your paper:
 Shown as capital letters.
 Example:

 Big “T,” Big “B,” or Big “W”
Recessive
The “weaker” allele. A recessive trait
only shows up when both alleles for a
trait are recessive.
Go to #10 on your paper:
 Shown as lower case letters.
 Example:

 Little “d,” Little “b,” or Little “w”
Genotype
The two alleles for a trait. These are
shown as two letters.
 Example: TT, Tt, tt,…

Phenotype
The result of the alleles for a trait. How
the trait shows itself. How it looks.
 Example: tall, short, yellow, green,
wrinkled,…

Pure
When each allele passed on by the
parents is the same.
 Example: TT, gg, or hh

 Pure Dominant: TT, GG, or HH
 Pure Recessive: tt, gg, or hh
Hybrid
When each allele passed on by the
parents is different.
 Example: Tt, Gg, or Hh

Dominant Alleles

To show a dominant allele as a
genotype: Use upper case letters

Examples: TT, BB, RR
Recessive Alleles

To show recessive alleles in a genotype:
Use lower case letters.
Examples: tt, bb, rr
Rules of Genotypes
1. Use letters to represent the alleles.
Any letters can be used.
 2. Capital letters (upper case) represent
the dominant allele.
 3. Lower case letters are used to
represent the recessive allele.
 4. If two alleles are the same for a trait
(LL, tt, ee,…) these are called pure.

Rules of Genotypes Continued
5. If two alleles are different for a trait
(Ll, Tt, Ee,…) these are called hybrid.
 6. Always write the dominant allele first.
(Bb, NOT bB)
