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Genetics Vocabulary
Vocabulary
Word
Genetics
Definition
Other Things to
Know…
The field of Biology
devoted to
understanding how
traits are passed
from parents to
offspring
Gregor Mendel
-pioneer in
genetics
-crossed peas to
show how traits
were passed on
Gregor Mendel (1822-1884)


Austrian monk
Called the
“Father of
Genetics" for
his study of the
inheritance of 7
traits in pea
plants.
Gregor Mendel (1822-1884)

The traits that Mendel chose to study
were easily observable in 2 distinct
forms.
EX.: Stem Height - tall vs. short
Pod Shape - round vs. wrinkled
Flower Color – white vs. purple
Seed Color – green vs. yellow
Gregor Mendel (1822-1884)


The significance of
Mendel's work was
not recognized
until the turn of
the 20th century
Its rediscovery
prompted the
foundation of
genetics.
Vocabulary
Word
Heredity
Definition
Other Things to
Know…
The transmission of Important for
traits from parents
understanding
to their offspring
reasons for our
appearance and
study of genetic
diseases
vocabulary terms
INHERITANCE or
HEREDITY- The
genetic
transmission of
characteristics
from parent to
offspring, such as
hair, eye, and
skin color.
Vocabulary
Word
Trait
Definition
A category within
which alternate
characteristics can
be observed
Other Things to
Know…
Examples of
traits:
hair color,
eye color,
height
Vocabulary
Word
Gene
Definition
A segment of DNA
that contains coding
for a polypeptide or
protein – a unit of
hereditary
information
Other Things to
Know…
Found on
chromosomes
within the
nucleus
vocabulary terms
HOMOLOGOUS
CHROMOSOMEA pair of matching
chromosomes in
an organism, with
one being
inherited from
each parent.
vocabulary terms
AUTOSOMEA chromosome
that is not a sex
chromosome.
Vocabulary
Word
Definition
An alternate form
of a gene
Alleles
Other Things to
Know…
Ex: Everyone
has an eye color,
but there are
different types:
blue, brown, etc.
vocabulary terms

ALLELES- alternative forms of the
same gene. Alleles for a trait are
located at corresponding positions on
homologous chromosomes called loci.
ALLELES
Chromosome
from MOM
A
A
b
B
C
c
d
d
e
E
Chromosome
from DAD
(P)
Chromosome
from DAD: P
Chromosome
from MOM: p
(p)
Vocabulary
Word
Definition
An allele that masks
the presence of
Dominant another allele
for the same
characteristic
Other Things to
Know…
-Shown with a
capital letter
(ex: A, T, G).
-Will always be
seen if present.
What are Dominant Genes?


Dominant Genes = one gene
overshadows the other
Angus Cattle: black is dominant, red
is not
Dominant: BB or Bb
Recessive: bb ONLY
What are Dominant Genes?
Hereford: white face is dominant
Dominant: WW or Ww
Recessive: ww ONLY
Vocabulary
Word
Recessive
Definition
Other Things to
Know…
An allele that is
masked by the
presence of another
allele for the same
characteristic
-Shown with a
lower case letter
(ex: a, t, g).
-Will only be
seen if both
alleles for a trait
are recessive.
What are Recessive Genes?
Black wool is recessive to white wool.
Dominant: WW or Ww
Recessive: ww ONLY
What are Recessive Genes?

Albinism (Albino) is recessive to
pigmented.
Vocabulary
Word
Definition
Law stating that
pairs of genes
Law of
separate in meiosis
Segregation and each gamete
receives one gene
of a pair
Other Things to
Know…
Allows each
parent to
contribute half the
chromosomes to
produce offspring
with the full # of
chromosomes.
Vocabulary
Word
Definition
Law stating that
pairs of genes
Law of
separate
Independent independently of
Assortment one another in
meiosis
Other Things to
Know…
The gene for
eye color sorts
separately
from hair color,
and skin color,
etc…
Vocabulary
Word
Genotype
Definition
Other Things to
Know…
The genetic makeup
of an organism
Written with the
letters of alleles:
Aa, TT, bb, etc.
vocabulary terms
GENOTYPE- the genes present in the
DNA of an organism.
There are always 2 letters in the
genotype because (as a result of sexual
reproduction)
1 gene from MOM + 1 gene from DAD = 2
genes (2 letters) for offspring
vocabulary terms
Now, it turns out there are 3 possible
GENOTYPES:

TT = homozygous = purebred

Tt = heterozygous = hybrid

tt = homozygous = purebred
Vocabulary
Word
Definition
The external
(physical)
appearance of an
Phenotype
organism that is
determined by the
individual’s
genotype
Other Things to
Know…
Written as the
Physical Trait:
Brown hair,
blue eyes,
short, etc.
vocabulary terms

PHENOTYPE- how the trait
physically shows-up in the organism;
it is the observable traits present in
an organism
What the organism LOOKS like

Examples of phenotypes: blue eyes,
brown fur, striped fruit, yellow flowers
Vocabulary
Word
Definition
Referring to a gene
pair in which the
Homozygous two alleles code
for the same trait
Other Things to
Know…
Written as:
AA or aa
Vocabulary
Word
Definition
Other Things to
Know…
Referring to a gene Written as:
pair in which the
Aa
Heterozygous two alleles do not
code for the same
trait
Vocabulary
Word
Purebred
Definition
An organism that is
homozygous for
a trait
Other Things to
Know…
Ex: AA or aa
Vocabulary
Word
Hybrid
Definition
An organism that
is heterozygous
for a trait
Other Things to
Know…
Ex: Aa
Genotype
Symbol
TT
Tt
tt
Genotype
Vocabulary
homozygous
DOMINANT
or
purebred tall
heterozygous
or
hybrid
homozygous
RECESSIVE
or
purebred short
Phenotype
tall
tall
short
Vocabulary
Word
Definition
The number of times
an event is expected
Probability to happen divided
by the number of
opportunities of an
event to happen
Other Things to
Know…
Ex: dice,
coin-flipping,
chance of have
blue eyes, etc.

Geneticists apply mathematical
principles of probability to Mendel’s
laws of heredity in order to predict the
results of simple genetic crosses



Mendel’s laws of heredity are based on
his mathematical analysis of
observations of patterns of the
inheritance of traits.
The laws of probability govern simple
genetic recombinations.
To see this we use a Punnett Square
Vocabulary
Word
Punnett
Square
Definition
A model used to
establish the
probabilities of the
results of a genetic
cross
Other Things to
Know…
Mom’s alleles
go together on
one side and
Dad’s go together
on the other.
Punnett Squares
•
For the pea plant flowers:
dominant: purple color = P
recessive: white color = p.
•
If both parents are purebred, then
the purple colored parent must be PP
and the white colored parent must be
pp.
How can we predict these results?
Homozygousdominant
We complete the
possible combinations.
Homozygousrecessive
p
p
P
P
Pp
Pp
Pp
Pp
These results show that all the F1 (1st
filial generation) offspring are all
purple colored hybrids.
p
P
Pp
P
Pp
p
Pp
Pp
100% purple offspring
We can use another
Heterozygous - hybrid
Punnett square to
predict the F2 (2nd filial
generation) offspring.
Heterozygous - hybrid
P
p
P
p
PP
Pp
pp
Pp
The results are always
Heterozygous - hybrid
mathematically the
same, a 3:1 ratio with
75% purple & 25%
white offspring
Heterozygous - hybrid
P
p
P
p
PP
Pp
pp
Pp
Phenotypic ratio 3:1
Genotypic ratio 1:2:1