Name: _________________________
Pd. _________
The Basics of Genetics
KEY CONCEPTS:
-Heredity is the passing of traits from parent to offspring.
-Some traits are inherited
Example: eye color, blood type, hair color, shape/size of nose, body type...etc.
-Some traits are acquired (or developed through your life; not born with it)
Example: learning how to read/write, basketball skills, speed of typing...etc.
**You can NOT pass on acquired traits through DNA**
-Individuals do not receive the traits, themselves, from their parents. They receive the genes that code for
the traits it has.
-Each human has 23 pairs of chromosomes
-The 23rd pair are the sex chromosomes—yes, these chromosomes determine the gender of the offspring,
however, they do play other roles as well.
-Gregor Mendel- founder of the idea behind genetics and performed multiple experiments with breeding
plants to witness the different traits produced.
KEY TERMS:
Sexual reproduction: the type of reproduction in which male and female reproductive cells combine to
form offspring with genetic material from both cells.
Gene: the basic unit of heredity that consists of a segment of DNA on a chromosome.
Heredity: The passing of genes from parents to offspring; the genes are expressed in the traits of the
offspring.
Chromosomes: come in pairs. Each member in that pair is called a homolog.
Alleles: alternate forms of the same gene (example: Bb, Hh, Tt...etc.)
Phenotype: the observable characteristics or traits of an organism (examples: eye color, color of flower,
height...etc.)
Genotype: the genes that an organism has (Example: BB, Hh, TT...etc.)
Dominant: one version of the gene trumps the other (always written in capital letters: B, H, T)
Recessive: the allele is not expressed in the phenotype when combined with a dominant form of a gene.
Punnett Square: a visual representation of how the parents’ alleles might combine in offspring. Consists
of squares that are used to create combinations of genes, such as recessive and dominant.
Ratio: compares or shows the relationship between two quantities (usually written as 4:4 or four to four)
Probability: the likelihood, or chance, of a specific outcome in relation to the total number of possible
outcomes.
Percentage: a ratio that compares a number to a 100. It states the number of times a particular outcome
might happen out of 100 chances.
Basics to Punnett Squares
1. Begin by drawing a table that has 4 boxes->
2. Recognize that each box makes up 25% or 1/4 (think of adding the 4 together, you’re given
100% or 4/4. This will help you with determining the end probability/ratio/percentage.
3. Read the information that is provided to you.
Example: There are two parent bunnies. Each parent bunny has one dominant allele for black fur
(B) and one recessive allele for brown fur (b)
**Remember, dominant genes will be written with capital letters, whereas recessive genes
will be written with lower case letters. **
3. After reading the information, begin properly filling in your Punnett square (male’s genes
usually go on the top).
4. After you fill in your Punnett square, determine the probability/ratio/percentage of which
trait will be passed onto the offspring.
5. What will its phenotype be? How can you determine this?