SCIENCE - GENETICS
GIMME A “D”! GIMME A “N”! GIMME AN “A”!
WHAT’S THAT SPELL?
DNA - THE CODE OF LIFE!
INTRO TO GENETICS
Essential Question #1
Ok, sorry to disappoint you, but we’re not going to break into a big CHEERLEADING practice. It’s
time to get serious about a serious topic: GENETICS!
Understanding GENETICS means that you have to understand heredity. HEREDITY is what
controls the traits and characteristics of organisms as they reproduce and produce new generations of
organisms. In other words, we are going to find out WHY you [and other organisms] look the way you
[they] do…and, in some cases, WHY you [and other organisms] are able to do the things you [they]
do. To do this, we are going to study THE CODE OF LIFE: Deoxyribonucleic Acid…THE MATTER
IN THE CELLS OF EVERY ORGANISM THAT CARRIES THE CODE – THE INFORMATION –
ABOUT THE TRAITS AND CHARACTERISTICS OF THE ORGANISM!
The first essential question of our study of genetics is:
WHO AND WHAT MAKE UP THE BASIC PRINCIPLES
(i.e.THE FOUNDATION) OF GENETICS?
To answer the WHO part of this question, let’s refer to our GENETICS SOCIAL STUDIES journal
entry and DISCUSS the contributions of some of the most important people in the history of genetics.
 Gregor Mendel
 Reginald C. Punnett
 Karl Correns
 Walther Flemming
 Walter Sutton
 Thomas Hunt Morgan
 Hugo DeVries
 James Watson
 Francis Crick
 Rosalind Franklin
 Ian Wilmut
 Barbara McClintock
SOOOOOOOOO, now that we know a little about the WHO of the foundation of genetics, let’s
talk about the WHAT…get ready for the FOUNDATIONAL GENETIC TERMS! Understanding these
terms is key to understanding GENETICS. Below and on the next page are tables of these important
genetic terms that belong in some of he blanks within the notes that follow – you need a good grip on
them so your genetics journey is a successful one!
TRAIT
CHROMOSOMES
ALLELE
OFFSPRING
GENE
1) A __TRAIT _________ is a physical characteristic of an organism.
2) A __GENE ____ is general category of a characteristic of organism. They are found on
chromosomes. They are the units of heredity that determine the traits of an organism and they come in
pairs.
3) _CHROMOSOMES_ , which can be rod-shaped (chromatids) or thread-like (chromatin), are structures
in the nucleus of an organism’s cells. They also come in pairs and are made up of DNA - a molecule
consisting of nitrogenous bases and phosphate and sugar molecules.
4) Each of the parents of an _OFFSPRING _______ donate one of the chromosomes in the
chromosome pair (one chromosome comes from the father and one chromosome comes from the mother).
5) Organisms of the same specie have the ___SAME__ amount of chromosomes in EVERY ONE of their
cells. Organisms of different species have a _DIFFERENT____amount of chromosomes in their cells.
ALL humans have 46 chromosomes (_23__ pairs) in their body (i.e. somatic) cells and _23___ in their sex
cells (i.e gametes). All fruit flies have 8 chromosomes (_4_ pairs) in their body (i.e. somatic) cells and
__4_ in their sex cells (i.e. gametes).
CHROMOSOME PAIR
7) The member of each gene pair that determines a specific trait is called an___ALLELE______. For
example in the case of hair color for humans, a person could have an _ALLELE__ for brown hair and an
_ALLELE___ for blond hair (think ahead…what type of hair do you think the person ACTUALLY has?).
DOMINANT
RECESSIVE
PUREBRED
HYBRID
GENOTYPE
INCOMPLETE DOMINANCE
PHENOTYPE
8) In a gene pair, the stronger or more likely to be seen of the two traits is called _DOMINANT___ and
the weaker or less likely to be seen of the two traits is called ___RECESSIVE_______. We express the
dominant trait or allele with a capital letter and the recessive trait or allele with the lowercase letter of
the letter used for the dominant trait! For example, Mendel (aka “The Father of Genetics”) studied the
characteristic of height in pea plants. Tall plants were dominant and short plants were recessive. The
abbreviation for tall was “_T_” and for short was “__t_”.
9) The ___PHENOTYPE___ describes what the organism’s traits actually look like physically (think
“ph”… “face”), but the __GENOTYPE________ is what the makeup of the gene pair is (think
“geno”…”gene”). A pea plant with a gene pair or alleles Tt for height has a __PHENOTYPE_____ of
being tall (looks tall), but a __GENOTYPE__ of being made up of one dominant and one recessive allele.
10) A ___PUREBRED___ organism will occur when the gene pair contains two alleles that are that are
the same. For example, for a __PUREBRED ___ tall pea plant the abbreviation for the gene pair that it
has for the trait of height is “_TT_.” If it is a mix of alleles (i.e. one dominant and one recessive allele),
the organism is called a ___HYBRID______. For plant height this would be expressed as “_Tt__.”
Remember, the letter you choose depends upon the name given to the dominant trait and the
recessive trait uses the same letter and NOT the first letter of its name. In the case of a plant that is a
HYBRID in height, using “Ts” would be ABSOLUTELY WRONG!
11) Sometimes, you can get an offspring that has what we call __INCOMPLETE_ _DOMINANCE__. In this
case, you get offspring that have a characteristic that is a blend of the characteristics of the
parent organisms. For example, sometimes when a flower that is white is bred with the same
specie (i.e. type of) flower that is red…you end up getting a flower that is PINK! Neither color is dominant
or recessive!
CODOMINANT
MUTATION
MUTAGEN
12) Sometimes an offspring will have a trait that is __CODOMINANT_______ . This means that BOTH
characteristics of the alleles in the gene pair are expressed. They do not mix or blend their
traits as in incomplete dominance; they are both __DOMINANT____. They are equally “strong” and
evident in the __PHENOTYPE___ (appearance) and ___GENOTYPE___ (genetics) of the organism for
that trait. An example of this is blood type in humans!
13) And, last but not least…sometimes genetics goes AWRY and a _MUTATION__ occurs. A
___MUTATION___ is a “mistake” or a change in the gene or chromosome of an organism. Genes
in the chromosome during a __MUTATION____ can be DELETED and REATTACHED to a different
chromosome or LOST or TURNED AROUND/FLIPPED! As a result, the organism MAY end up having a
a characteristic that is not normally seen in its population. NOT ALL _MUTATIONS_ lead to changes in an
organism (think about why this is so!).
____LOST______
___TURNED AROUND__
____REATTACHED__
14) It is important to know that mutations can be inherited! It is also important to know that they can
occur naturally or because of a factor in an organism’s environment like pollution or solar radiation.
This factor is called a ____MUTAGEN________. Sometimes mutations are helpful and produce a
new trait in a species that helps it to survive better. An example is SEEDLESS oranges (don’t you just
hate seeds in your oranges?). Helpful mutations are tied in with the idea that groups of organisms
evolve and and the “fitter” ones with better traits will survive (i.e. a la Darwin, survival of the fittest, and
natural selection - topics that you will study next year!)
15) Sometimes mutations can even lead to a NEW specie! HOWEVER, sometimes mutations
can be dangerous…for example, sickle cell anemia – a disease of human blood – is the result of a
mutation.
OK…one more important BASIC PRINCIPLE of GENETICS…
It’s important to remember one more idea about genetics and inheritance…Each
gene is inherited independently from other genes...genes are NOT inherited
together! For example, blue eyes and blond hair are _NOT___ inherited
TOGETHER…that’s why we have so many different combinations of hair and eye color! Because of
this ability to get SO MANY different combinations of traits, genetics is often referred to as a case of
PROBABILITY and, as a result, scientists are able to use their mathematical skills to predict the
outcome of an organism’s traits! But…that prediction stuff is coming in another lesson…for now,
let’s take a break and make sure that we aren’t suffering from
of our “basic principles of genetics” vocabulary.
and practice some
TABLE OF GENETIC TERMS
Putting your knowledge to use!
DOMINANT
HYBRID
PHENO GENO
RECESSIVE
PUREBRED
PHENO GENO
HEIGHT
Tall – T
Short – t
Tall
TT
Tall
Tt
Short
tt
SEED
SHAPE
Round – R
Wrinkled - r
Round
RR
Round
Rr
rr
SEED
COLOR
Yellow – Y
Green - y
SEED
COAT
COLOR
Colored – C
White – c
POD
SHAPE
Full – F
Pinched – f
POD
COAT
COLOR
FLOWER
POSITION
YY
Yellow
RECESSIVE
DOMINANT
ALLELE
PUREBRED
(name and PHENO GENO
symbol)
Cc
Green
White
FF
Green – G
Yellow – g
Green
GG
Side – S
End – s
Side
SS
Pinched
Full
Yy
yy
cc
Colored
CC
Colored
TRAIT
Yellow
DOMINANT
ALLELE
(name and
symbol)
Wrinkled
PART I. Place the correct letter, letter combination, or trait description in the empty boxes below. Refer to
page E19 of your book in order to determine the dominant and recessive alleles for each trait!
Full
Ff
ff
Green
Gg
Yellow
gg
Side
Ss
End
ss
TEST OF YOUR TRUE/FALSE GENETIC TERM KNOWLEDGE!
PART II. Use your notes to determine if the UNDERLINED parts of the following statements about the
foundations of genetics are true or false. If they are true, write ”TRUE” in the blank next to each
statement. If they are false, write “FALSE” in the blank next to each statement and, in the lines below the
statement, change the statement to be true by crossing out or adding genetic terms or descriptions above
or below each statement.
__FALSE__ 1. Our DNA (i.e. the material of our chromosomes) is made up of nucleic acids (proteins) and
sugar and phosphate molecules.
__FALSE__ 2. Chromosomes are found in the nucleus.
__TRUE___ 3. Mendel was a monk who studied pea plant characteristics and because of his findings he
is known as the “Father of Genetics.”
__TRUE___ 4. Our traits and characteristics are determined by our genes.
__FALSE__ 5. Genes come in pairs and they are located on our chromosomes.
___FALSE__ 6. Humans have 46 chromosomes in every body cell.
__FALSE___ 7. An offspring will inherit half of its chromosomes from its father and half from its mother.
__FALSE___ 8. Incomplete dominance occurs when the offspring has a BLEND of its parents’ traits.
__TRUE ___ 9. Codominance of traits results in the display of BOTH alleles because BOTH alleles are
dominant. An example of codominance is blood type in humans.
__FALSE__ 10. Mutations can occur naturally as well as the result of environmental factors called
mutagens.
__TRUE___ 11. Mutations happen when parts of chromosomes are turned around, deleted, or placed on
another chromosome.
__TRUE___ 12. Mutations can produce both positive AND negative results.
_FALSE__ 13. Genes for different traits are inherited separately. For example, the genes for skin color is
separately from the genes for hair color.
__FALSE__ 14. Genetics is based on the principles of probability.
SCIENCE - GENETICS
WHEN IT COMES TO GENETICS BEING SQUARE IS COOL!
THE PUNNETT SQUARE
A method for predicting the genetic outcome of organisms!
PUNNET SQUARE NOTES AND PRACTICE
Essential Question #2
NOTES:
In the study of genetics, we have a handy-dandy method of predicting the possible genotypes and
phenotypes of offspring for any given trait IF we know the genotype of the parents! This method is based
on probability (Oh no! Math and science together! Yes, once again it’s possible for two subjects to be used
together!).
In our intro to genetics (the foundation of who’s and what’s!), we heard about a geneticist, Reginald C. “Not
so Square” Punnett, and the fact that he is responsible for developing what we refer to as the PUNNETT
SQUARE method. This method is used to help scientists predict what the traits of an offspring will be
before the organisms comes to exist! Cool, HUH? It’s like being able to tell the future (well, not really,
it’s really just about being good at drawing squares and placing letters in correct boxes)!
To make a Punnett square and be able to predict the possible offspring that could result from breeding two
organisms of the same specie, do the following steps:
T
T
1) Draw a square and divide it into four boxes.
2) List the one allele from the gene pair from one
parent next to the two boxes on the left side
of the large square. For the example, we are
starting with one parent that is a hybrid tall pea plant.
T
TT
TT
t
Tt
Tt
3) List the other two alleles from the gene pair of
other parent above each box at the top of the
large square. For the example, we are supposing
that we are crossing our hybrid with a purebred tall
pea plant.
4) Write the alleles from the top and sides of the square in the boxes
where they intersect. Remember only ONE allele comes from EACH parent!
5) Use your results to predict the probable PHENOTYPES and GENOTYPES of your four possible
organisms! Use percentages or fractions to explain the probability of getting certain
phenotypes and genotypes in the offspring.
OUTCOME
PROBABILITY
(% and fraction)
Phenotype
Tall
%
100
fraction
4/4
Phenotype
short
%
0
fraction
0/4
Genotype
Purebred Tall
%
50
fraction
2/4
Genotype
Hybrid
%
50
fraction
2/4
Genotype
Purebred
Recessive
%
0
fraction
0
IN CLASS PRACTICE! Let’s be square and give this Punnett Square method a try!
B
B
1) A black-haired purebred guinea pig is crossed
with a white-haired guinea pig. In guinea pigs,
b
Bb
Bb
black hair is the dominant trait. What are the
possible phenotype and genotype outcomes
for such a combination?
b
Bb
Bb
OUTCOME
PROBABILITY
(% and fraction)
Phenotype
Black
%
100
fraction
4/4
Phenotype
White
%
0
fraction
0
Genotype
Genotype
Purebred
Hybrid
Dominant
fraction %
fraction
%
0
0
100 4/4
S
2) Mendel discovered that wrinkled seeds
in pea plants are recessive to smooth seeds.
If a parent plant that is a hybrid for seed type
is crossed with another hybrid, what will the
possible organism outcome be?
s
S
SS
Ss
s
Ss
OUTCOME
PROBABILITY
(% and fraction)
Phenotype
Smooth
%
75
fraction
¾
Phenotype
Wrinkled
%
25
fraction
¼
3) In humans, blue eyes are not as dominant
as brown eyes. If a blue-eyed man has a child
with a blue-eyed woman, what will the possible
outcomes of eye color in their offspring be?
OUTCOME
PROBABILITY
(% and fraction)
Phenotype
Brown
%
0
fraction
0/4
Phenotype
Blue
%
100
fraction
4/4
Genotype
Purebred
Recessive
fraction
%
0
0
ss
Genotype
Genotype
Purebred
Hybrid
Dominant
fraction %
fraction
%
25
¼
50
¼
b
b
b
bb
bb
b
bb
bb
Genotype
Genotype
Purebred
Hybrid
Dominant
fraction %
fraction
%
0
0
0
0
Genotype
Purebred
Recessive
Fraction
%
25
¼
Genotype
Purebred
Recessive
Fraction
%
100 4/4
HOMEWORK PRACTICE! Be square and give this Punnett Square method a try AT HOME!
1) A gray-haired purebred cat is crossed
with a white-haired purebred cat. In cats,
grey hair is the dominant trait. What are
the possible phenotype and genotype
outcomes for such a combination?
G
g
g
OUTCOME
PROBABILITY
(% and fraction)
Phenotype
Grey
%
100
fraction
4/4
Phenotype
White
%
0
fraction
0
Gg
Gg
Gg
Gg
Genotype
Genotype
Purebred
Hybrid
Dominant
fraction %
fraction
%
0
0
100 4/4
2) Mendel discovered that green pea pods
in pea plants are dominant to yellow pea pods.
If a parent plant that is a hybrid for pod color is
crossed with a parent plant that is recessive for
pod color, what will the possible organism outcomes be?
OUTCOME
PROBABILITY
(% and fraction)
Phenotype
Green
%
50
fraction
½
Phenotype
Yellow
%
50
fraction
½
G
G
g
Gg
g
Gg
g
gg
gg
Genotype
Genotype
Purebred
Hybrid
Dominant
fraction %
fraction
%
0
0
50
½
3) In horses, brown coats and white coats are
neither dominant nor recessive. What would
happen if you crossed a purebred brown coat
B
horse with a purebred white coat horse? __you’d get a offwhite coat__
Predict the possible outcomes for coat color
for the offspring of these two horses.
B
What type of dominance would this be? _INCOMPLETE DOMINANCE_
OUTCOME
What will the color will ALL the
offspring (phenotype) be?
COLOR: __off-white____
PROBABILITY
(% and
fraction)
%
100
fraction
4/4
Genotype
Purebred
Recessive
fraction
%
0
0
Genotype
Purebred
Tall
%
0
fraction
0
Genotype
Purebred
Recessive
fraction
%
50
½
W
W
BW
BW
BW
BW
Genotype
Hybrid
%
0
fraction
0
Genotype
Purebred
Recessive
%
0
fraction
0