Genetics Is the Science of How Traits Are Passed From

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%_____