Transcript Chapter 9: Introduction to Genetics

Chapter 11: Genetics
Understanding Genetics
Genetics – the branch
of biology that studies
heredity (the passing on
of traits from parent to
offspring)
11-1: The Work Of Gregor Mendel
• a.k.a. “Father of Genetics”
• Founded Modern Genetics
• Monk who worked in a
monastery ; in charge of the
garden
• Grew over 28,000 pea plants
(Pistum sativum) and studied
their unique characteristics
passed from one generation to
the next.
• See pg 309 in Macaw Biology
book for further details
Before we continue…
 It is important to remember that we get half
our genetic material from MOM and the other
half from DAD.
 Therefore, we have two genes* for each trait
we have.
 We presently know this because of Mendel.
*Sometimes we have more than two genes for each trait but
we’ll talk about that later.
Homozygous/Heterozygous
• The two genes for the same trait
are called alleles.
• These alleles can have the same
form or contrasting forms.
• If the alleles are the same, they
are called HOMOZYGOUS or
Pure for that trait
• If the alleles are contrasting, they
are called HETEROZYGOUS or
Hybrid for that trait.
Dominant and Recessive Genes
• Some alleles can be dominant meaning they
code for the more influential trait.
• Some alleles can be recessive meaning they
code for the more subtle trait.
• For example: Brown eyes are dominant over
green or blue eyes.
Applying Mendel’s Genetics
There are two factors that determine
everything about an organism:
1) Heredity - what you inherit
Examples of thing you inherit:
Color of hair, skin, eyes, height, frame size,
handedness, disease/disorder, tongue-rolling, IQ,
shape of teeth, athleticism, vision, # of digits.
2. Environment - what you acquire
• Examples of things you acquire:
Ability to play an instrument,
skills of a sport, disability/illness,
job skills.
• Things you inherit can sometimes
be influenced by your
environment.
• Ex. You can inherit strong bones
but if you do not get the proper
nutrition, your bones may
become weak and brittle.
Twins reared apart
• Both wear rubber bands around their left wrist
• Both married “Lindas” and divorced then married
“Marys”
• Both read magazines from back to front
• Both had miscarriage same day & year
• Both drove the same car
• Both had the same occupation (gym owners)
• Both had short mustaches
• Both cross their eyes when they laugh
• Both dance the same and have same mannerisms
Traits - features or characteristics that organisms
have. There two basic types of traits:
1) Species Traits - common to
all members of a species.
Ex. Feathers on birds, # of legs,
chromosomes, appendages,
body form.
2) Individual Traits differences among
members of a species.
Ex. Color of feathers,
size of legs, location
and texture of fur/hair,
pigmentation, athletic
ability, IQ.
Watchung Reservation
Nov. 15, 2008
Probability - is the likelihood that a
particular event will occur.
• Formula:
P = The number of times a particular event occurs
The number of total trials
• Ex. Flipping a coin
• What is the probability of getting “tails”?
1/2 or 1:1
Important Rules of Probability:
• The previous event has NO impact on future
outcomes. Each event is a separate,
independent event.
• The larger the number of trials, the closer
you get to the expected ratios.
4 box Punnett square word problems
Right-handedness is dominant over left-handedness.
Cross a male who is homozygous (pure) right-handed
with a female who is lefty. What are the phenotypic
and genotypic ratios and percentages of the possible
offspring?
Phenotype/Genotype
• Phenotype: % of the appearance of an individual.
(two categories: Dom. Vs. Rec)
• Ex. Righty vs. Lefty
• Genotype: % of the genetic possibilities of the
individual (3 categories: pure dom., hybrid, rec.)
• Ex. Pure Righty vs. Hybrid Righty vs. Lefty
How To Do A Genetics Problem
1. Show a key:
• The first letter of the dominant trait is
capitalized to represent the trait.
Ex. Right-handedness = R
• The small (lowercase) letter of the dominant
trait is used to represent the recessive trait.
Ex. Left-handedness = r
r
R
KEY:
• RR = Right handed, dominant pure (homozygous)
• Rr = Right handed, dominant hybrid (heterozygous)
• rr = Left handed, recessive, (always pure/homozygous)
2. Show the parent’s traits:
RR
X
rr
3. Show segregation (into sex cells)
rr
RR
R
R
r
r
4. Punnett’s Square
R
r
r
Rr
R
Rr
Rr
Rr
5. Ratio of offspring:
Phenotype - the outward appearance of the organism.
(dominant or recessive)
Phenotypic % and Ratio=
4 righty : 0 lefty(4:0)
or
100% to 0%
Genotype - the genetic mix of genes.
(pure dominant, hybrid dominant, or recessive)
Genotypic % and ratio =
0 pure/righty: 4 hybrid/righty: 0 lefty (0:4:0) or
0% : 100% : 0%
Problem: Crossing the F1 generation:
Right-handedness is dominant over left-handedness. Cross a female
and male who are both hybrid right-handed. What are the
phenotypic and genotypic ratios of their possible offspring?
1. Key:
RR = pure/dominant righty
Rr = hybrid/dominant righty
rr = pure/recessive lefty
2. Parents:
3. Segregation:
Rr
R
X
r
Rr
R
r
R
r
4. Punnett
R
r
RR
Rr
Rr
rr
5. Ratio & Percentage:
Phenotype: 3: 1 or 75% : 25%
Genotype: 1:2:1 or 25% : 50% : 25%
A cross between two hybrids is called a monohybrid
cross and it will always have the same ratio & % as
the problem above.
Monohybrid 4 box Punnett Square
Problem
Problem: Long horns is dominant over shorthorns in
cattle. Cross a male and female who are both
heterozygous for this trait.
1. KEY:
• LL = pure dominant long horns
• Ll = hybrid dominant long horns
• ll = recessive short horns
2. PARENTS:
Ll X Ll
3-4. Punnett:
L
l
L
LL
Ll
l
Ll
ll
Phenotype: 3 : 1 or 75%: 25%
Genotype: 1: 2: 1 or 25%: 50%; 25%
• Testcross –
– crossing an individual of unknown genotype with
a recessive individual (which is always pure) to
determine the genotype of the unknown.
Problem: Black fur is dominant over white fur in rats. If you have a
black rat, how can you find out if she is homozygous (BB) or
heterozygous (Bb)?
Answer: Mate her with a recessive colored rat and then check the ratio
of the offspring!
2 possible genotypes for your pet rat are:
BB or Bb
B
b Bb
b Bb
B
Bb
Bb
B
b
Bb
b
bb
b
Bb
bb
Testcross Results
BB X bb =
• Phenotype: 4:0
• Genotype: 0:4:0
Bb X bb =
Phenotype: 2:2
Genotype: 0:2:2
• If your black rat has 100% black offspring,
she is BB. If she has any white offspring, she
must be Bb.
Co-dominance
Roan colored fur
• In horses, fur color is co-dominant. Cross a brown
colored horse and a white colored horse. What is the
phenotypic % of the offspring?
• Key:
BB= Brown fur
B = Roan Fur
Cross the F1 generation. What is the phenotypic % of
the F2 generation of offspring?
Incomplete Dominance
a.k.a.
Blending
• In parakeets, feather color exhibits incomplete
dominance. Cross a blue parakeet with a yellow
parakeet. What is the phenotypic % of the offspring?
• Key:
BB= blue feathers
YY= yellow feathers
BY = green feathers
Both co-dominant and
incomplete dominance
Parakeets can also exhibit codominance AND incomplete
dominance so sometimes
they exhibit multi-colors.
Multiple Alleles
Each person can have
only two versions of a
multiple allele trait in
their genome at one
time, but in the
population there are 3
forms.
Example: Blood types (
A, B,& O)
Blood Typing
• Karl Lansteiner (1868 -1943) won the Nobel
Prize in 1930 for his discovery of blood
groups.
Antigens
• Antigens are proteins that can be found on your Red
Blood Cells (RBC).
• If you have antigen A, you have Type A blood.
• If you have antigen B, you have Type B blood.
• If you have both antigen A and B, you have Type
AB blood.
• If you do not have either antigen A or B, you have
Type O blood.
Four Types of Blood
• Type A
• Type AB
Type B
Type O
Rh Factor
Several years later,
Landsteiner found
another antigen on the
RBC while studying
Rhesus monkey
blood.
He named the
protein after the
monkey calling it
the Rh factor.
If you have the
Rh factor you are
considered Rh+.
If you don’t have
it, you’re Rh-.
Rh factor in pregnancies
The Rh- mother will produce anti-Rh antibodies.
Causing hemolytic disease of the newborn this can lead to brain
damage, mental retardation, and even death.
What’s your Type?
Ready for Multiple
Allele Punnett
squares?
Genotypes
• When writing the genotypes of multiple alleles
, you use the letter “I” for the dominant and
letter “i” for the recessive.
• The A, &/or B is shown as a superscript.
• The “I” stands for "isoagglutinogen". This is
another word for a blood group antigen in the
ABO system.
How to write genotypes for Blood type
genetics problems
This is always your key!
•
•
•
•
•
•
IA IA = type A blood, pure dominant
IA i = type A blood, hybrid dominant
IB IB = type B blood, pure dominant
IB i = type B blood, hybrid dominant
IA IB = type AB blood, co-dominant
i i = type O blood, recessive
Multiple Allele Problems
• A man with Type AB blood marries a
woman with type O blood.
• Using a key & Punnett square, show the
cross between these two parents and give the
phenotypic % of their possible offspring.
Pedigree Analysis
Genetics
What is a Pedigree?
A pedigree is a diagram of family
relationships that uses symbols to represent
people and lines to represent genetic
relationships.
These diagrams make it easier to visualize
relationships within families, particularly
large extended families. Pedigrees are often
used to determine the mode of inheritance
(dominant, recessive, etc.) of genetic
diseases.
• In a pedigree, males are represented by
squares and females by circles .
• An individual who exhibits the trait in
question, for example, is represented by a
filled symbol
or
In the pedigree here, the
grandparents had two
children, a son and a
daughter. The son had
the trait in question. One
of the son’s children also
had the trait.
Oldest
individuals
Oldest
individuals
Vertical lines extending downward from
a couple represent their children.
Subsequent generations are therefore
written underneath the parental
generations and the oldest individuals
are found at the top of the pedigree.
All 4 are the
youngest generation
Again…
For Example
Dominant and Recessive Traits
 Using genetic principles, the
information presented in a
pedigree can be analyzed to
determine whether a given
physical trait is either dominant
or recessive.
Dominant Traits :
 Characteristics of a dominant pedigree are:
1) Every affected individual has at least one
affected parent;
2) Affected individuals who mate with
unaffected individuals have a 50% chance of
transmitting the trait to each child; and
3) Two affected individuals may have
unaffected children.
A dominant trait
is passed on to
a son or
daughter from
only one parent.
Recessive Traits
• Recessive traits are passed on to children from both parents,
although the parents may seem perfectly "normal."
• Characteristics of recessive pedigrees are:
– 1) An individual who is affected may have parents who are
not affected;
– 2) All the children of two affected individuals are affected;
and
– 3) In pedigrees involving rare traits, the unaffected parents of
an affected individual may be related to each other.
Outsider Rules
• In any pedigree there are people whose parents are unknown. These
people are called “outsiders”, and we need to make some assumptions
about their genotypes.
• Outsider rule for dominant pedigrees: affected outsiders are assumed
to be hybrid.
• Outsider rule for recessive pedigrees: unaffected (normal) outsiders
are assumed to be homozygotes.
• Both of these rules are derived from the observation that mutant
alleles are rare.
Sample Pedigree Problems
------------------ ------------------
1.The pedigree below is studying the incidence of blonde hair
in a family. In humans, dark hair (B) is dominant to blonde
hair (b). In this case, individuals who are shaded in are
homozygous recessive. Individuals who have clear circles
and squares have at least one dominant gene.
What are the genotypes of persons A through F above?
Answer
• Explanation:
• Person B is blonde, because they are shaded in. They are thus
homozygous recessive (hh).
• Persons C through F must have at least dominant allele (H). Without
more information, this would make them HH or Hh.
• Person B can only provide the h alleles to its eggs, so persons C-F
must be heterozygous (Hh).
• Without more information, Person A who is dominant must be HH or
Hh.
Interesting Fact:
The Story of Hemophilia
• Late in the summer of 1818, a human sperm and egg
united to form a human zygote. One of those gametes, we
don't know which, was carrying a newly mutated gene. A
single point mutation in a nucleotide sequence coding for
a particular amino acid in a protein essential for blood
clotting. The zygote became Queen Victoria of England
and the new mutation was for hemophilia, bleeder's
disease, carried on the X chromosome.
• A century later, after passing through three generations, that
mutation may have contributed to the overthrow of the Tsar and
the emergence of communism in Russia. Victoria passed the gene
on to some of her children and grandchildren, including Princess
Alexandra, who married Nicholas II, Tsar of Russia, in 1894.
• By 1903, the couple had produced four daughters. The next year,
the long awaited male heir appeared - His Imperial Highness
Alexis Nicolaievich, Sovereign Heir Tsarevich, Grand Duke of
Russia. From his father, the baby Alexis inherited the undisputed
claim to the throne of all the Russias.
• From his mother, Alexis inherited an X chromosome carrying a
copy of the mutant gene for hemophilia. Soon after his birth, signs
of Alexis' mutant gene appeared. At six weeks, he experienced a
bout of uncontrolled bleeding and by early 1905 the royal
physicians had concluded that he was suffering from hemophilia.
Sex-linked Traits
•Traits carried on the X chromosome.
•More prevalent in males because they only have 1 X chromosome
Color vision is dominant over color deficiency
and is sex linked.
Cross a female who is a carrier of the disorder but
who has normal vision with a male who is
colorblind.
Show the key, parents, punnett and phenotype and
genotype percentages for all offspring.
(Remember you must separate males from
females)
Sex-linked Problem2
•
•
•
Normal blood clotting is dominant over hemophilia
and is sex linked. Cross a pure dominant female
with a male hemophiliac. Show the key, parents,
Punnett and phenotype and genotype percentages
for their sons and daughters.
If one of the sons (F1 generation) marries a woman
who is a hemophiliac, what is the chance that his
sons (F2 generation) will have normal blood?
__________
Why?
_________________________________________
___________________
Sex-linked: Hemophilia
Pedigree Problem 2:
To the right is a
pedigree for an
inherited lung
disease. Provide
the genotypes of
each of the
individuals
marked with lower
case letters.
•
•
•
•
•
Solution to Problem 2
a) aa
b) Aa
c) Aa
d) A? (in other words AA or Aa)
16 Box Punnett Square Problem
Set Up
Word Problem #1
• Purple flowers are dominant over
white flowers in pea plants.
• Axial Flower growth is dominant over terminal
(top) flower growth.
• Cross a “female” who has pure purple flowers
and is hybrid axial for flower growth with a
“male’ who has white flowers and is a terminal
(top) flower grower.
• What are the possible phenotypes of the
offspring?
Step 1: Key
•
•
•
•
•
•
PP = pure dom. Purple
Pp = hybrid dom. Purple
pp = recessive White
AA = pure dom. Axial
Aa = hybrid dom. Axial
aa = rec. top growing
Step 2: Parents
PPAa
ppaa
Step 3: Segregation
• Order Rule 1:
• Cross:




1+3
1+4
2+3
2+4
PPAa
1
PA
Pa
2
3
PA
4
Pa
Step 4: Punnett Square
PA
pa
pa
pa
pa
PpAa
Pa
PA
Pa
Step 4: Punnett Square
pa
pa
pa
pa
PA
Pa
PA
Pa
PpAa
Ppaa
PpAa
Ppaa
PA
Pa
PA
Pa
pa
PpAa
Ppaa
PpAa
Ppaa
pa
PpAa
Ppaa
PpAa
Ppaa
pa
pa
PA
Pa
PA
Pa
pa
PpAa
Ppaa
PpAa
Ppaa
pa
PpAa
Ppaa
PpAa
Ppaa
pa
PpAa
Ppaa
PpAa
Ppaa
pa
PA
Pa
PA
Pa
pa
PpAa
Ppaa
PpAa
Ppaa
pa
PpAa
Ppaa
PpAa
Ppaa
pa
PpAa
Ppaa
PpAa
Ppaa
pa
PpAa
Ppaa
PpAa
Ppaa
Phenotypic Ratio
• Order Rule 2:
• Categories:
Dom. of trait 1 with dom. of trait 2
Dom. of trait 1 with the rec. of trait 2
Rec. of trait 1 with the dom. of trait 2
Rec. of trait 1 with the rec. of trait 2
Phenotype:
Trait 1: Purple flowers are dominant over
white flowers in pea plants.
Trait 2: Axial Flower growth is dominant over
terminal (top) flower growth.
Dom. of trait 1 with dom. of trait 2
Dom. Of trait 1 with the rec. of trait 2
Rec. of trait 1 with the dom. of trait 2
Rec. of trait 1 and rec. of trait 2
Purple and Axial:
Purple and Top:
White and Axial:
White and Top:
pa
pa
pa
pa
PA
PpAa
PpAa
PpAa
PpAa
Pa
Ppaa
Ppaa
Ppaa
Ppaa
Purple and Axial:
Purple and Top:
White and Axial:
White and Top:
PA
PpAa
PpAa
PpAa
PpAa
8
8
0
0
Phenotypic Ratio is
8:8:0:0
Pa
Ppaa
Ppaa
Ppaa
Ppaa