Genetics… What is it?
Genetics is the science of how traits are passed from
parents to offspring. Gregor Mendel was the first to
experiment with genetics and heredity and is
considered the Father of Genetics. He performed
thousands of experiments with pea plants,
studying characteristics such as height, color,
and seed shape. Mendel’s work in the 1860s lead him to
develop the basic principles of genetics.
Genetics Basics
An organism’s physical characteristics are called traits.
You get your traits from your parents. Each trait you have, eye
color, etc, has 2 genes. One gene comes from mom, the other
from dad. The genes hold the DNA, which is the genetic
information that determines everything about you… even the
fact that you are HUMAN! Genotype describes the genetic
makeup (gene pair) of a trait. Phenotype describes the
physical outcome of the trait.
Dominant vs. Recessive
Traits are either dominant (strong) or recessive (weak). For example,
brown eyes are dominant over the recessive blue eyes. We use letters to
represent the traits when writing about them. Dominant traits use capital
letters, and recessive traits use lowercase letters. So we would
represent brown eyes (dominant) by B and blue eyes (recessive)
by b. Remember we inherit 2 genes (a gene pair) for each trait.
So from what are the possible combinations you could inherit from
your parents (when the choices are B and b)?
_BB______ ___Bb___ __bb_____ ___bB____
inherited genes
phenotype
genotype
BB
Brown eyes
Brown, brown
Bb
Brown eyes
Brown, blue
bB
Brown eyes
Blue, brown
bb
Blue eyes
Blue, blue
B = brown eyes
b= blue eyes
Incomplete dominance – This is the condition in which both
genes in the gene pair are partially shown. Neither one covers up
the other completely. For example, a red 4 o’clock and a white 4 o’clock can
cross pollinate and produce pink 4 o’clocks.
Predicting Genetic Outcomes
Predicting is knowing or telling of something in advance, based on
inferences. Scientists use probability (the chance of an event occurring)
and predicting to give the possible outcomes of a genetic cross. For
example, if a couple has a child, we can predict what sex the child will be.
The hereditary traits an organism will have can be predicted by using a
Punnett square.
x
x
x
xx
xx
y
xy
xy
Dad = male, xy
Mom = female, xx
What is the probability of having a male child? ___2/4____ = ___50%____
What is the probability of having a female child? ___2/4____ = ___50%____
B
b
b
Bb
bb
b
Bb
bb
Dad= brown eyes, Bb
Mom = blue eyes, bb
What is the probability of having a brown eyed child? ___2/4____ = __50%___
What is the probability of having a blue eyed child? ____2/4___ = ___50%_____