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Genetics
• Genetics – study of how traits are passed from parent
to offspring
• Traits are determined by the genes on the
chromosomes. A gene is a segment of DNA that
determines a trait.
• Chromosomes come in homologous pairs, thus genes
come in pairs.
Homologous pairs – “matching” genes – one from
female parent and one from male parent
• Example: Humans have 46 chromosomes or 23 pairs.
One set from dad – 23 in sperm
One set from mom – 23 in egg
• One pair of Homologous Chromosomes:
Gene for eye color
(blue eyes)
Homologous pair
of chromosomes
Gene for eye color
(brown eyes)
Alleles – different genes (possibilities) for the same trait –
ex: blue eyes or brown eyes
Genetics Notes
Who is Gregor Mendel?
“Father of Genetics”
Principle of Independent Assortment – Inheritance of one
trait has no effect on the inheritance of another trait
Principle of dominance – some traits “hide” other traits
Results for One Trait
Dominant and Recessive Genes
• Gene that prevents the other gene from “showing” –
dominant
• Gene that does NOT “show” even though it is present –
recessive
• Symbol – Dominant gene – upper case letter – T
Recessive gene – lower case letter – t
Dominant
color
Recessiv
e color
Example: Straight thumb is dominant to hitchhiker thumb
T = straight thumb t = hitchhikers thumb
(Always use the same letter for the same alleles—
No S = straight, h = hitchhiker’s)
Straight thumb = TT
Straight thumb = Tt
Hitchhikers thumb = tt
* Must have 2 recessive alleles
for a recessive trait to “show”
• Both genes of a pair are the same –
homozygous or purebred
TT – homozygous dominant
tt – homozygous recessive
• One dominant and one recessive gene –
heterozygous or hybrid
Tt – heterozygous
BB – Black
Bb – Black w/
white
gene
bb – White
Genotype and Phenotype
• Combination of genes an organism has (actual gene
makeup) – genotype
Ex: TT, Tt, tt
• Physical appearance resulting from gene make-up –
phenotype
Ex: hitchhiker’s thumb or straight thumb
Punnett Square and Probability
• Used to predict the possible gene makeup of offspring –
Punnett Square
• Example: Black fur (B) is dominant to white fur (b) in mice
1. Cross a heterozygous male with a homozygous recessive female.
Black fur (B)
Heterozygous
male
White fur (b)
White fur (b)
Homozygous
recessive female
White fur (b)
Male = Bb X Female = bb
b
Male gametes - N
(One gene in
sperm)
B
b
b
Bb
Bb
bb
bb
Female gametes – N
(One gene in egg)
Possible offspring – 2N
Write the ratios in the following orders:
Genotypic ratio = 2 Bb : 2 bb
50% Bb : 50% bb
Genotypic ratio
homozygous : heterozygous : homozygous
dominant
recessive
Phenotypic ratio = 2 black : 2 white
50% black : 50% white Phenotypic ratio
dominant : recessive
Sex Determination
• People – 46 chromosomes or 23 pairs
• 22 pairs are homologous (look alike) – called autosomes –
determine body traits
1 pair is the sex chromosomes – determines sex (male or female)
• Females – sex chromosomes are homologous (look alike) – label XX
Males – sex chromosomes are different – label XY
Try This…

When you are told, place the small
piece of paper on your tongue.

What happened?

How many in the classroom can taste
something?

How many cannot taste anything?
Traits

The ability to taste PTC is an inherited trait.
There are two forms of the trait:

Let T = taster (dominant form)

Let t = non- taster (recessive form)

Traits are determined by genes. For each
inherited trait, you get one form of the gene
(an allele) from each of your parents.

Your phenotype is either taster or nontaster

Your genotype is TT or Tt if you are a taster,
or tt if you are a nontaster.
Cross 2 hybrid mice and give the genotypic ratio and
phenotypic ratio. Black Fur (B) is dominant over white fur
(b)
Bb X Bb
B
b
B
BB
Bb
b
Bb
bb
Genotypic ratio = 1 BB : 2 Bb : 1 bb
25% BB : 50% Bb : 25% bb
Phenotypic ratio = 3 black : 1 white
75% black : 25% white
Incomplete dominance and Codominance
• When one allele is NOT completely dominant over
another (they blend) – incomplete dominance
Example: In carnations the color red (R) is incompletely
dominant over white (W). The hybrid color is
pink. Give the genotypic and phenotypic ratio from a
cross between 2 pink flowers.
RW X RW
R
R
W
RR RW
W RW WW
Genotypic = 1 RR : 2 RW : 1 WW
Phenotypic = 1 red : 2 pink : 1 white
• When both alleles are expressed – Codominance
Example: In certain chickens black feathers are
codominant with white feathers.
Heterozygous chickens have black and white speckled
feathers.
Sex – linked Traits
• Genes for these traits are
located only on the X
chromosome (NOT on the Y
chromosome)
• X linked alleles always show
up in males whether
dominant or recessive
because males have only
one X chromosome
• Examples of recessive sex-linked disorders:
1. colorblindness – inability to distinguish between certain
colors
You should see
58 (upper left),
18 (upper right),
E (lower left) and
17 (lower right).
Color blindness is the inability to
2. hemophilia – blood won’t clot
• Example: A female that has normal vision but is a carrier
for colorblindness marries a male with normal vision.
Give the expected phenotypes of their children.
N = normal vision
n = colorblindness
XN Xn X XN Y
XN
Xn
XN XNXN
XNXn
XNY
XnY
Y
Phenotype: 2 normal vision females
1 normal vision male
1 colorblind male
Crazy Traits

The alleles you inherit from each parent
are determined by chance.

In this investigation, you will play a game
that will help you learn about
inheritance.
Your creature’s gender

Find the egg coin (x on both sides)

Find the sperm coin (x on one side, y on the other)

Flip the coins together to determine the gender of your
creature.

Record this in the table provided – see next slide for
example
Determining trait genotypes for
your creature

Members of this species have the following traits:
main body, foot, leg, skin, arms, hands, beak, eyes,
eyebrows, ears, wings, antenna.

You will flip sperm and egg coins to determine the
allele for each trait your creature inherits from
each parent.
Determining trait genotypes for
your creature

In this activity, we will assume that both parents have the same
genotype for all traits (Tt).

The genotype of each parent could be Tt, TT, or tt. We are choosing
to have parents with the Tt genotype for each trait.
Determining the genotype for
each trait

You will need the blue egg coin with a capital T on one side and a
lower case t on the other side.

You will also need the green sperm coin with a capital T on one side
and a lower case t on the other side.
Determining the genotype for a
trait

The first trait you will roll for is skin color.

Place the egg and sperm coins in the cup.

Shake the cup and toss the two coins onto the lab table.

The side that lands up on each coin represents the sperm and egg that unite
during fertilization.
Determining the genotype

Record the allele from each parent and genotype in columns 2, 3, and 4 of the
first row of Table 1.

Repeat this procedure for traits 2 through 13.

See the next slide for an example.
Stop and Think
a.
What information do the letters on the sperm and egg coins
indicate: alleles, genotype, or phenotype?
Alleles.
Both alleles together represent the genotype.
Stop and Think
b. For the sperm coin, what are the chances of getting a T or getting a t?
State your answer as a fraction or a percent.
1/2 or 50%.
Stop and Think
c. For the egg coin, what are the chances of getting a T or getting a t?
State your answer as a fraction or a percent.
1/2 or 50%.
Stop and Think
d. When both coins are
flipped at once, what
are your chances of
getting each of the
following combinations:
TT, Tt, or tt? State your
answer for each as a
fraction and a percent.
Building your creature

Once you have completed columns 2 through 4 of Table 1, use
Table 2 (next page) to look up the phenotype for each trait.
Record the phenotype for each trait in column 5 of Table 1.
Building your creature

Once you have completed Table 1, select the correct body parts
to build your creature. See parts list on next slide.
Creature Building Tips
1.
2.
3.
4.
5.
6.
7.
Orient the body for either male or
female (which orientation do you think
is male? Female?)
Place the skin on the smooth side of the
body.
Attach the head.
Attach the leg.
Place foot on the stand.
Insert the leg into the foot and stand.
Attach the rest of the body parts.
Thinking about what you observed
a. Examine the creatures. Do any of them look exactly
alike? Why or why not?
 Some look similar, but no two are alike. For two to
look exactly alike, every single flip of all three coins
would have to be the same for both creatures. That
seems very unlikely.
Thinking about what you observed
b. How does this investigation explain why siblings may
resemble each other, but never look exactly alike
(unless they are identical twins)?
 Since siblings share the same parents they will likely
share many of the same traits. With the huge
amounts of traits possible for humans the
probability of all of them matching from sibling to
sibling is very small.
Thinking about what you observed
c. Count the number of males and number of females.
Does the number of each match the chances of
getting a male or female in the game? Why or why
not?
 Not exactly because the sample is small. Larger
samples yield results that are closer to the average.
Thinking about what you observed
d. Which trait(s) are examples of complete
dominance?
 Eyebrows, beak, ears, leg, foot, arms, hands,
antennae, antenna shape, wings, and gender.
e. Which trait(s) are examples of incomplete
dominance?
 Skin color and tail.
f. Which trait(s) are examples of codominance?
 Eye color.
Adaptation Survivor
1.
Environment Cards will be displayed on this screen.
For each card, your creature can: thrive (+1 point); be
pushed closer to extinction
(-1 point); or have no effect (0).
2.
Watch out for Catastrophe Cards!
3.
When you earn a score of -3, you become extinct!
4.
Play until there is one survivor left.
 YOUR
BRIGHT PURPLE SKIN IS
NOTICABLE TO PREDATORS IN
YOUR ENVIRONMENT!
 Purple
skin -1


There is a food shortage on land. Those
with webbed feet are able to swim to
catch food.
(If you have webbed feet +1, talons -1)