QOD 1/23/13
Do
the Genetics Quiz
on your note packet
QOD 1/23/13- TRUE OR FALSE?
1.
2.
3.
4.
5.
6.
7.
8.
9.
Girls inherit more traits from their mother than their
father
You have inherited traits that are not apparent
Color blindness is more common in males than
females
Identical twins are ALWAYS the same sex
A person can transmit genetic traits to their offspring
which they themselves DO NOT show
The father determines the sex if a child
The total number of male births exceeds female births
each year
Acquired characteristics, like mathematical skills, can
be inherited
Fraternal twins are more closely relates to each other
than to other siblings
Genetics
The field of Biology
devoted to understanding
how characteristics are
passed from parents to
offspring
Gregor Mendel



In the 19th century, Mendel studied hereditywhich is the transmission of characteristics
from parent to offspring
Mendel is most famous for studying pea plants
He studied what he called “factors” in pea
plants
–
Factors would be things like tall or short (height), or
yellow or green (pod color)
 Some
of
Mendel’s
Factors
Gregor Mendel

First, Mendel grew true-breeding plants
– According to Mendel, true-breeding plants
are plants that will always produce
offspring with the same traits
– So a true-bred pea plant with purple
flowers will only produce plants with purple
flowers because it only has the “factors” for
purple (not white).
Gregor Mendel- P generation

Mendel bred two opposite true-breeding plants

For example, he bred a true-breeding purple
flower pea plant and a true-breeding white
flower pea plant
He called this his P generation
(parent generation)

Gregor Mendel- F1
generation



All of the offspring of the P generation (which
he called the F1 generation) turned out
purple
Mendel called purple flower color the
dominant factor
He hypothesized that when the dominant
factor was present, the recessive factor
(white color) did not show.
Gregor MendelF2 generation


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Next, Mendel crossed the offspring from the
F1 generation (he called this the F2
generation)
He observed that about 75% of the flowers
were purple and about 25% were white
This is equal to about a 3:1 ratio
P Generation
(true-breeding
parents)
F1 Generation
(hybrids)
F2 Generation
Purple White
flowers flowers
All plants had
purple flowers
Mendel’s Laws



Keep in mind that Mendel knew nothing of
Punnett squares, genes, alleles, or even DNA!!!
All he could do was observe phenotypes and
record ratios and other statistics
He came up with 2 important laws as a result of
his observations.
Mendel’s LawsLaw of Segregation

Mendel concluded that each plant gets two
factors (alleles) for a characteristic and when the
plant reproduces, these two factors separate or
segregate. So…
– Each gamete (sex cell) gets one factor (allele)
AND therefore…
– Each offspring gets one factor from each
parent
Law of Segregation is shown in
Punnett Squares
Mendel’s LawsLaw of Independent Assortment



Mendel did experiments using more than one
trait (like height and seed color)
He noticed that one trait did not influence the
inheritance of another trait
In other words, different factors separate
independently of each other during the
formation of gametes
Mendel’s LawsLaw of Independent Assortment

Examples:
– Pea plants can be short or tall
– Their seeds can be green or yellow
– Short plants can have green or yellow seeds
– Tall plants can have green or yellow seeds
– So the inheritance of one does not affect the
inheritance of the other.
– Mendel noticed this with all the traits he
studied
Mendel’s
Laws-

Independent Assortment is not always true– If different genes are located on the same
chromosome, then they will most likely be
inherited together
– These are called Linked Genes
QOD 1/24/13
 If
a true-breeding tall plant has
offspring, will they be tall or short?
What were Mendel’s factors in
reality?

We call these alleles today
–
–

Alleles are alternative forms of a gene
Alleles for flower color were purple and white
The characteristics (like height) are caused
by genes on DNA
–
–
Genes are segments of DNA that code for one
protein
Each gene has 2 alleles, or versions (1 from
mom and one from dad)
What were
Mendel’s factors
in reality?

The reason alleles come in pairs is because
chromosomes come in pairs (homologous
pairs)!!
– One allele on each chromosome!
– WHAT A COINCIDENCE!!!
The Genetics of Mendel’s Experiments
Some Vocab
– Dominant trait- masks the recessive
 Shown
–
Recessive trait- only shows if dominant is
not present
 Shown
–
with capital letters
with lower case letters
Phenotype- physical appearance
 For example purple, wrinkled, tall, etc
The Genetics of Mendel’s Experiments
Some Vocab
– Genotype- genetic makeup
 This is usually abbreviated with letters like
Gg, FF, or hh
 Genotypes for a trait are usually 2 letters
because you get 2 alleles (1 from mom and 1
from dad)
– Homozygous- two of the same alleles (like HH
or hh)
– Heterozygous- two different alleles (like Hh)
The Genetics of Mendel’s Experiments
Homozygous dominant means 2 BIG letters

Heterozygous means one big one little

Homozygous recessive means 2 little letters

If an organism shows the dominant trait, then
they can be either heterozygous OR
homozygous dominant
QOD 2/1/12
 Which
of these is homozygous?
(may be more than one answer)
1. AA
2. Aa
3. aa
Genetics Video

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1. pea plant
2. each parent give one trait and traits can be
dominant or recessive
3. traits
4. fruit flies
5. fly eye color is sex-linked
6. bread mold
Genetics Video
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7. unable to produce nutrients because no
enzymes
8. DNA creates enzymes
9. corn
10. the move
11. jumping genes
12. bacteria
Genetics Video
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13. 1; 2
14. sperm + egg
15. 23
16. 23
17. fertilized egg
18. 46
19. that’s how the zygote grows
Genetics Video
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20. same as #2
22. hybrid
23. black
24. white
26. 1 or 25%
27.music
28. no
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29. DNA causes genetics
30. humans changing
DNA
31. shows genes on DNA
32. find bad sequences
33. replacing bad genes
34. messing with DNA
might have bad results
QOD 1/25/13
 TAKE
 If
OUT YOUR NOTES
Short (l) is recessive and long
(L) is dominant, what is the
phenotype for Ll?
The Genetics of Mendel’s Experiments
 Mendel’s
P generation had the
genotypes FF (for purple) and ff (for
white)
– True breeding is also homozygous
FF is homozygous dominant
ff is homozygous recessive
The Genetics of Mendel’s Experiments
We can show the results Mendel observed
using a Punnett Square:
– A Punnett Square shows possible genetic
combinations in the zygotes
– Mendel crossed his true breeding purple
and white flower pea plants
 We write this as FF x ff
FF x ff
•During Meiosis, alleles separate (when
homologous chromosomes separate), to show this,
we can separate the letters
•The offspring from this mating can only get one
letter (allele) from each parent
FF x ff
If we put the
gametes into a
Punnett
Square, then
we can show
the possible
combinations
FF x ff
•Other Info:
•Capital Letters
always go first
•It doesn’t matter
which side you put
each parent on
•All offspring are Ff,
which is
heterozygous and
will be purple
Ff
Ff
Ff
Ff
Each square
represents a possible
zygote (offspring)
QOD 1/29/13

TURN IN PENNY LAB (PROBABILITY LAB)

What is the difference between heterozygous
and homozygous?
Predicting Genetics

Sometimes worksheets will ask for the
percentages
– It will be 0, 25, 50, 75, or 100%
– 0 out of 4 = 0%
– 1 out of 4 = 25%
– 2 out of 4 = 50%
– 3 out of 4 = 75%
– 4 out of 4 = 100%
The Genetics of Mendel’s Experiments
What Mendel did not know:
– All of F1 pea plant flowers heterozygous
(two different alleles), or Ff
 That is why they were all purple
– Remember dominant alleles mask
recessive alleles
 So with one purple allele present and
one white, only purple would show as it
is dominant
The Genetics of Mendel’s Experiments

Punnett Square for the
F2 generation:
– Ff x Ff (from F1 gen)
– 3 of the 4 squares
would have purple
flowers, while1 would
have white flowers
– That’s 75% purple,
25% white flowers
FF
Ff
Ff
ff
F2 generation

Phenotypic ratio:
– This means how
many dominant to
how many recessive
– In this example, it
would be 3:1
– Note- the “:” means
“to”
FF
Ff
Ff
ff
F2 generation

Genotypic ratio:
– XX : Xx : xx (or,
homozygous dominant
to heterozygous to
homozygous recessive)
–
In this example, it
would be 1:2:1
FF
Ff
Ff
ff
Punnett Square Examples

Let’s do a Punnett square for BB x Bb
– B= black fur in bunnies
– b= white fur in bunnies
– So black fur is dominant
Punnett Square Examples

Phenotypic ratio:

Genotypic ratio:

What are the chances
of a white bunny?
Punnett Square Examples



Phenotypic ratio:
– 100% black bunnies
(4:0)
Genotypic ratio:
– 2BB:2Bb:0bb = 1:1:0
What are the chances
of a white bunny?
– 0%
BB
Bb
BB
Bb
Punnett Square Examples
 Let’s
look at a heterozygous
cross
– Bb
x Bb
Punnett Square Examples
 Bb
x Bb
–
Phenotypic ratio:
–
Genotypic ratio:
–
What are the chances
of a white bunny?
–
What are the chances
of a black bunny?
Punnett Square Examples




Phenotypic ratio:
– 3 black :1 white = 3:1
Genotypic ratio:
– 1BB:2Bb:1bb = 1:2:1
What are the chances of
a white bunny?
– 25% (1 in 4)
What are the chances of
a black bunny?
– 75% (3 in 4)
BB
Bb
Bb
bb
Predicting the Results of Heredity

What do these ratios and percents mean?
– If we flip a coin, there is a 50% chance that it will
land on heads. But it is still possible to get 5 tails in
a row (although it is highly UNLIKELY!)
– The more times you flip it, the more likely your
results will be 50:50
– If Bb and Bb bunnies mate, there is a 1:4 chance
the offspring will be white (this does NOT mean
that they will or will not have white bunnies)
– If they have LOTS of children, about 25% of them
will be white
QOD 1/29/13
 Take
out your HOMEWORK! I
will come around and check it
 What
is the phenotypic ratio if
two heterozygous parents have
children?
Predicting Dihybrid Crosses

When 2 traits are being looked at…

Let’s do a cross between two
heterozygous tall, heterozygous purple
flowered pea plants
– So, TtFf x TtFf
Predicting Dihybrid Crosses

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Instead of 2 possible gametes, there will be 4
So, the Punnett Square will be 4 x 4
TtFf
Predicting Dihybrid Crosses
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Phenotypic Ratios
– Tall, purple : tall,
white : short,
purple : short,
white
Keep same letters
together, capitals 1st
You will not be asked
for genotypic ratios
for dihybrid crosses
Predicting Dihybrid Crosses

Phenotypic Ratio
– 9:3:3:1
 This
is always
the ratio in a
hybrid x hybrid
dihybrid cross
TTFF TTFf TtFF
TtFf
TTFf
TTff
TtFf
Ttff
TtFF
TtFf
ttFF
ttFf
TtFf
Ttff
ttFf
ttff
QOD 2/6/13
 TAKE
 What
OUT NOTES
is the difference between
complete and incomplete
dominance?
Complex Inheritance
Mendel observed
monogenic traits and no
linked genes…It’s not
usually that simple….
Other Types of Inheritance

Incomplete Dominance
–
–
–
The phenotype of the heterozygote is
intermediate between phenotypes of the
homozygotes
Example: when a homozygous red carnation is
crossed with a homozygous white carnations,
then pink carnations are produced
We usually don’t use lower case letters in this
type of inheritance because nothing is really
dominant
Incomplete Dominance



RR = Red
RW= pink
WW= white
Incomplete Dominance Punnett
Square
Pink x White
 RW x WW

50% offspring
are pink
– 50% are white
RW
RW
WW
WW
–
Other Types of Inheritance

Codominance
– Occurs when both alleles for a trait are
expressed in heterozygous offspring
– Codominant alleles are often symbolized
with different letters
Codominance



BB = Brown
BW= Roan
WW= White
Notice both brown and white are present in the heterozygote
Codominance Punnett Square
Roan x Roan
 BW x BW

25% brown
– 50% roan
– 25% white
BB
BW
BW
WW
–
Other Types of Inheritance

Multiple Alleles:
– Genes with 3 or more alleles (or
variations)
– Human blood type shows codominance
and it has multiple alleles- A, B, and O
Blood Type

Human blood types have 3 alleles A, B, and O.
– Each person still only gets 2 alleles, but there
are 3 possibilities
– O is recessive to A and B,
– A and B are codominant:
– Genotype AO or AA = A blood
– Genotype BO or BB = B blood
– Genotype OO = O blood
– Genotype AB = AB blood (both alleles
expressed)
Blood Type
Blood Type
Terminology
GENOTYPE
Heterozygous B
BO
Heterozygous A
AO
Homozygous recessive
OO
Homozygous A
AA
Homozygous B
BB
AB (technically heterozygous)
AB
Codominance Punnett Square


Heterozygous A x
Heterozygous B
AO x BO
– 25% AB
– 25% A blood
– 25% B blood
– 25% O blood
AB
BO
AO
OO
QOD 2/11/13
 Flower
color in carnations shows
incomplete dominance. When a red
carnation mates with a white
carnation, what color are there
offspring?
Other Types of Inheritance

Sex-Linked Genes and Traits
– Remember sex chromosomes are the
chromosomes that determine the sex of an
organism
– So these are traits/genes carried on sex
chromosomes
– These traits are symbolized using a
superscript on the X or Y, such as Xr or XR
Other Types of Inheritance

Sex-Linked Genes and Traits Examples:
– In fruit flies, the gene for eye color is on the X
chromosome. Red (XR) is dominant, white (Xr) is
recessive.
– To have white eyes, females must have the genotype
Xr Xr , or in other words TWO white alleles
– To have white eyes, males must have the genotype
Xr Y, or in other words ONE white allele
– This is why X chromosome sex-linked traits are more
common in males
Sex-linked Punnett Square




Homozygous red
eyed female x white
eyed male
XRXR x XrY
Notice, 50% males
and 50% females for
offspring
All offspring will have
red eyes
Xr
Y
XR
XRXr
XRY
XR
XRXr
XRY
Other Types of Inheritance

Polygenic Inheritance:
– Traits that are controlled by more than
one gene
– Most human traits are polygenic
– Examples are height, skin color, eye
color, and hair color
Other Types of Inheritance

Complex Characters:
– Characters that are influenced by
genetics AND the environment
– Skin color and height are examples
Other Types of Inheritance

Sex-Influenced Traits:
– Traits in which males and females show
different phenotypes even though they
have the same genotypes
– Baldness is an example- it is dominant in
men, but recessive in women
– The differences are mainly due to males
and females producing different hormones
(chemical signals)
Other Types of Inheritance

Single Allele Traits
– Traits where there is only one allele
– If you have the allele you have the traitthere is no recessive
– Huntington’s disease is an example
Chromosome Mutations

Chromosome mutations involve
changes in the structure of a
chromosome or the loss or gain of
a chromosome.
– Deletion: The loss of a piece of
chromosome due to breakage
– Inversion: A chromosomal
segment breaks off, flips
around, and reattaches
Translocation- A piece of chromosome
breaks off and reattached to a
nonhomologous chromosome
Nondisjunction- When a chromosome fails to
detach from its homologue during meiosis, so
one gamete gets an extra chromosome
Duplication: repeats a
chromosomal segment