Download What is a TRAIT?

Gregor Mendel: Known as “THE FATHER OF
GENETICS”.
- laid the foundations for the SCIENCE OF
GENETICS through his study of inheritance
patterns of traits in pea plants.
Mendel’s Experiments:

He prevented self-pollination and used another
method called Cross Pollination (the joining of
pollen and egg) from 2 different plants creating
what is called a Hybrid (an organism that
received 2 different forms of a genetic trait from
each parent).
What is GENETICS: The study of heredity or
inheritance of traits.

What is a TRAIT? A specific characteristic that
can be passed from parent to offspring.
What is HEREDITY (inheritance)?
Passing of traits from parent to offspring or from one
generation to the next. Genes are the coded
instructions that define our traits
How are genes inherited?
 Humans have 2 sets of chromosomes for a total of 46
chromosomes. Each parent contributes only 1 set of chromosomes
to their child.

 When a sperm cell (23 chromosomes) and an egg cell (23
chromosomes) join during fertilization, it results in a zygote (46
chromosomes).
The Principle of Dominance:
States that some traits are dominate and
others are recessive.
So what does this mean?
A dominant trait is a
trait that is visible &
expressed using a
capital letter (B).
A recessive trait is a trait that
is sometimes “hidden” & is
expressed using a lower case
letter (b)
PRINCIPLE OF SEGREGATION:
States that each pair of genes segregate or
separate during meiosis carrying only a single
copy of each gene.
Gene: section of chromosome that codes for a protein
which will indicate a genetic trait (ex. height of plant or
pea color).

Most organisms have 2 copies of every gene (on
each chromosome).
Alleles: A different form of the same gene (ex. tall or
short, yellow or green).
HOMOZYGOUS - organisms that have 2
identical alleles for a particular trait and are
called true-breeds (purebred).
(Genotype would read as HH or hh)
HETEROZYGOUS - organisms have 2 different
alleles for the same trait and are called hybrids.
(Genotype would read Hh)
PHENOTYPE – Refers to the physical
appearance of an organism. (Tall or short, yellow
or green, short tail or long tail)
GENOTYPE – Refers to the genetic make up of an
organism. (Tt, Ss)
PRINCIPLE OF PROBABILITY
Method used to predict the possible outcome of
genetic crosses (like flipping a coin – you have a
50/50 chance of heads or tails)
What is a Punnett Square?
 A tool or grid used to predict and compare the genetic variations that
will result in a cross of two organisms traits.

Punnett Squares
RED HEADS ( r ) vs BLONDES (R)
heterozygous
Genotypes
Rr - 50%
rr - 50%
Phenotypes
Red - 50%
Blonde - 50%
Dihybrid Cross (2 factors): a 16 square grid that is used to predict
and compare the genetic variations that will result when crossing 2
traits of two organisms.
RY
Ry
rY
ry
RY
Ry
rY
ry
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
PRINCIPLE OF INDEPENDENT
ASSORTMENT:

- States that traits are inherited
independently and accounts for
variation among plants and other
organisms.