Transcript Unit 04 Part I - yayscienceclass

Bellwork: Which fact interests
you the most and why?
Genetics
Mendelian Genetics &
Patterns of Inheritance
Biology And Society:
Testing Before Birth
–
Genetic testing



Allows expectant parents to test for possibilities in their
unborn child.
Includes amniocentesis and CVS.
Has risks associated with it.
The Role of Environment
–
Many human characteristics result
from a combination of heredity and
environment.
The Chromosomal Basis of
Inheritance
–
The chromosome theory of
inheritance states that
 Genes
are located at specific positions on
chromosomes.
 The behavior of chromosomes during meiosis
and fertilization accounts for inheritance
patterns.
Figure 9.23
Linked Genes
–
Linked genes


–
Are located close together on a
chromosome.
May be inherited together.
Sex chromosomes


Influence the inheritance of
certain traits.
Due to linkage
Gregor Mendel
1822-1884
Gregor Mendel
 He
was an Austrian monk. He is
important because carried out the first
important studies of heredity. He studied
plants because plants have male &
female parts so that they can reproduce
sexually.
 Was the first person to analyze patterns
of inheritance.
 Deduced the fundamental principles of
genetics
Peas In an Abbey Garden
–
Mendel studied garden
peas because
 These
plants are easily
manipulated.
 These plants can selffertilize.
Peas In an
Abbey Garden
–
–
–
Mendel carried out
some crossfertilization.
He also created truebreeding varieties of
plants.
Mendel then crossed
two different truebreeding varieties.
Peas In an
Abbey Garden
–
–
Mendel performed
many experiments.
He tracked several
characteristics in pea
plants from which he
formulated several
hypotheses.
Heredity

The passing on of characteristics from
parents to children (offspring).
Genetics

The branch of biology that studies heredity.
Traits
Inherited characteristics
Often represented by
single letters.
Examples
Tall plant = T
Short plant = t
Purple flowers = F
White flowers = f
Allele
The different forms of a gene for the same trait. For
example if we look at a particular plant’s flower color
we have two possibilities F (for purple flowers) and f
(for white flowers). One allele comes from the female
parent, one comes from the male parent.
Homozygous


Two alleles of the same trait are the
same
Example: TT or tt
Heterozygous


Two different alleles for the same
trait
Example Tt
Dominant


The allele that is always displayed in a mixed
(heterozygous Tt) cross.
Represented by an upper case letter ex: T
Tongue curling is a dominant trait.
Recessive


A gene that is only displayed if both alleles
are the same.
Represented by a lower case letter ex: t
The bent finger is dominant and the straight finger is recessive.
Question


Is “W” dominant or recessive?
Is “w” dominant or recessive?
Genetic Alleles and
Homologous Chromosomes
– Homologous chromosomes
• Have genes at specific loci.
• Have alleles of a gene at the same locus.
Phenotype



What the organism looks like.
Memory trick: PH in “phenotype” is like the
PH in “photo”
Example: red, white, furry, bald.
Genotype



The genetic constitution of the organism.
In other words the genes of that organism.
Memory trick: GEN in “genotype” is like
the GEN in “gene”
Example: RR, rr, Rr
Question

In a heterozygous cross of
short plants and tall plants
how would you represent the
trait with letters?
Question

In a heterozygous flower if the dominant trait’s
genotype was for a purple phenotype and the
recessive trait’s genotype was for a yellow
phenotype. What would the flower’s phenotype be?
P Generation



The parental generation
These are true breeding plants. They will always
produce the same traits.
They are homozygous for a trait YY or yy




F1
Generation
The first generation.
These result after a cross from two parents of the P
generation with different traits.
Heterozygous Yy
The F1 generation are often
referred to as hybrids as
they will have mixed
genotypes but the same
phenotype.
F2 Generation


These are the offspring of a cross between
the heterozygous F1 generation Yy X Yy
These offspring will have
mixed genotypes and
phenotypes.
Bellwork 11/18/10 - Week 15
Monohybrid Cross – 1 trait
Example: hair color
B (blue hair) dominant
b (white hair) recessive
Make A Punnett Square 
Genotype
Mother = BB
What is the mother’s phenotype?
Father = bb
What is the father’s phenotype?
Question

How do you set up a Punnett square for this
cross?
Make a Punnett I
(colors used in genotypes to help you to see where each one goes in the box)
Mother BB
(take one B and put it over each box)
B
b
B
b
Father bb
B = blue hair
b = white hair
Fill in the genotypes for each offspring
Make a Punnett I
(colors used in genotypes to help you to see where each one goes in the box)
Mother BB
(take one B and put it over each box)
b
b
Father bb
B = blue hair
b = white hair
B
B
bB
bB
bB
bB
What is the phenotype for each offspring?
Make a Punnett I
(colors used in genotypes to help you to see where each one goes in the box)
Mother BB
(take one B and put it over each box)
b
b
Father bb
B = blue hair
b = white hair
B
B
bB
bB
Blue Hair
Blue Hair
bB
bB
Blue Hair
Blue Hair
Question
1.
2.
How many white haired offspring are there?
How many blue haired offspring are there?
Answer
1.
2.
0
4 or 4/4
Answer


Both parents are Bb
They both have blue hair
Mendel’s First Law
The Law of
Segregation
This law states that
allele pairs separate
or segregate during
the formation of eggs
and sperm (gamete
formation), and
randomly come back
together (unite) at
fertilization.
Mendel’s Second Law
The Law Of
Independent
Assortment
Different traits
are inherited
separately
(independently)
of each other.
Mendel’s Third Law
The Law Of
Dominance
If a homozygous
dominant parent
(TT) is crossed
with a
homozygous
recessive parent
(tt) the offspring
will ALWAYS be Tt,
displaying the
dominant
phenotype.
Question
So how do we predict the probability of
offspring types between two parents?
Think about how we predict a coin flip:
 With a coin flip.
1 in 2 that it will be heads.

Punnett Square
Used to show all possible
combinations.
Question
There are two parents who are both
heterozygous for hair color, where blue was
B and white was b
 What is the genotype for each parent?
 What is the phenotype for each parent?
Make a Punnett II
(colors used in genotypes to help you to see where each one goes in the box)
Mother Bb
(take one B and put it over each box)
b
b
B
B
Father Bb
B = blue hair
b = white hair
Fill in the genotypes for each offspring What is the phenotype for each offspring?
Question
1.
2.
How many white haired offspring are there?
How many blue haired offspring are there?
Dihybrid Cross

Used for two traits
Example:
R (round) dominant
r (wrinkled) recessive
Genotype
Mother = RyrY
Father = RyrY
Y (yellow) dominant
y (green) recessive
What is the mother’s phenotype?
What is the father’s phenotype?
Dihybrid Cross

Used for two traits
Example:
R (round) dominant
r (wrinkled) recessive
Genotype
Mother = RYry
Father = RYry
Y (yellow) dominant
y (green) recessive
What is the mother’s phenotype?
What is the father’s phenotype?
Make a Punnett
(colors used in genotypes to help you to see where each one goes in the box)
R = round
r =wrinkled
Y = yellow
y = green
Mother RrYy
(take one allele pair and put it over each box)
Ry
rY
RY
rY
ry Ry
Father RrYy
RY
Fill in the genotypes & phenotypes for each offspring
ry
Question
1.
2.
3.
4.
How many round & yellow peas are there?
How many round & green peas are there?
How many wrinkled & yellow peas are
there?
How many wrinkles & green peas are
there?
Using a Testcross to Determine
an Unknown Genotype
–
A testcross is a mating between

An individual of unknown genotype and a homozygous
recessive individual.
The Rules of
Probability
– The rule of
multiplication
states that
• The probability
of a compound
event is the
product of the
separate
probabilities of
the independent
events.
Summary of Mendel’s laws
LAW
DOMINANCE
SEGREGATION
INDEPENDENT
ASSORTMENT
PARENT
CROSS
OFFSPRING
TT x tt
tall x short
100% Tt
tall
Tt x Tt
tall x tall
75% tall (TT & Tt)
25% short (tt)
RrGg x RrGg
round & green
x
round & green
9/16 round seeds & green
pods
3/16 round seeds & yellow
pods
3/16 wrinkled seeds & green
pods
1/16 wrinkled seeds & yellow
pods
Incomplete Dominance,
Codominance, Sex-Linked
Traits & Multiple Alleles
Beyond Mendel
Variations On Mendel’s Laws
– Some
patterns of genetic
inheritance are not
explained by Mendel’s
laws.
Incomplete Dominance
F1 hybrids have an appearance somewhat in
between the phenotypes of the two parents.
Example: snapdragons (flower)
red (RR) x white (rr)
R
R
RR = red flower
rr = white flower
r
r
Incomplete Dominance
R
r
r
R
produces the
_____ generation
All _____ = pink
(heterozygous pink)
Incomplete Dominance
ABO Blood Type: An Example of
Multiple Alleles and Codominance
–
Multiple
alleles are
traits that
are
controlled
by more
than two
alleles.
Multiple Alleles continued


Note: An individual can only have two alleles
for any given trait, but the population can
have many different alleles for that trait,
sometimes over 100 different alleles for a
single trait!
Examples: Rabbit coat color, feather color,
human hair color.
Codominance
– Two
of the human blood type
alleles exhibit codominance.
 Both
alleles are expressed in the
phenotype.
Codominance
Two alleles are expressed (multiple
alleles) in heterozygous individuals.
Example: blood type
1. type A = IAIA or IAi
2. type B = IBIB or IBi
3. type AB = IAIB
4. type O = ii
Codominance Problem
homozygous male Type B (IBIB)
x
heterozygous female Type A (IAi)
Example:
IB
IA
i
IB
Another Codominance Problem
• Example: male Type O (ii)
x
female type AB (IAIB)
Codominance

Question:
If a boy has a blood type O and his sister has
blood type AB, what are the genotypes and
phenotypes of their parents?

boy - type O (ii) X girl - type AB (IAIB)
Polygenic
Inheritance
– Polygenic
inheritance is the
additive effects of
two or more genes
on a single
phenotype.
Bellwork Pre-AP Biology
1.
2.
3.
A red flower (RR) is crossed with a white
flower (rr).
In the case of codominance what is the
phenotype of the offspring?
In the case of incomplete dominance what
is the phenotype of the offspring?
What generation is the offspring?
Sex-linked Traits
Traits (genes) located on the sex
chromosomes
 Sex chromosomes are X and Y
 XX genotype for females
 XY genotype for males
 Many sex-linked traits carried on
X chromosome

Sex-Linked Genes
–
Sex-linked genes


Are any genes
located on a sex
chromosome.
Were discovered
during studies on
fruit flies.
Sex-linked Traits
Example: Eye color in fruit flies
Sex Chromosomes
fruit fly
eye color
XX chromosome - female
Xy chromosome - male
Sex-linked Trait Problem








Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female)
XRY
x
XrXr
Remember: the Y chromosome inR males
X
y
does not carry traits.
RR = red eyed
XR
Rr = red eyed
rr = white eyed
Xy = male
Xr
XX = female
Sex-Linked Disorders in Humans
–
A number of human conditions result from
sex-linked (X-linked) genes.
Red-Green Color Blindness
Is
characterized by a malfunction of
light-sensitive cells in the eyes.
Duchenne Muscular Dystrophy
Is
characterized
by a
progressive
weakening and
loss of muscle
tissue.
Hemophilia
Is
a
bloodclotting
disease.
Female Carriers
What is a carrier? Why are females usually carriers?
Pedigree Charts
The family tree of
genetics
Family Pedigrees
–
Mendel’s
principles
apply to the
inheritance of
many human
traits.
A family pedigree
 Shows
the history of a trait in a family.
 Allows geneticists to analyze human traits.
What is a Pedigree?

A pedigree is a chart of the genetic history of
family over several generations.

Scientists or a genetic counselor would find out
about your family history and make this chart to
analyze.
Constructing a Pedigree
 Female
 Male
Connecting Pedigree Symbols
Examples of connected symbols:
 Fraternal
 Identical
twins
twins
Connecting Pedigree Symbols
Examples of connected symbols:
 Married
 Siblings
Couple
Example

What does a pedigree chart look like?
Symbols in a Pedigree Chart
 Has
the trait
 X-linked
 Autosomal carrier
 Deceased
Interpreting a Pedigree Chart
Determine if the pedigree chart shows an
autosomal or X-linked disease.
1.
–
If most of the males in the pedigree are affected the
disorder is X-linked
–
If it is a 50/50 ratio between men and women the
disorder is autosomal.
Example of Pedigree Charts

Is it Autosomal or X-linked?
Interpreting a Pedigree Chart
2.
Determine whether the disorder is dominant
or recessive.
–
If the disorder is dominant, one of the
parents must have the disorder.
–
If the disorder is recessive, neither
parent has to have the disorder
because they can be heterozygous.
Example of Pedigree Charts

Dominant or Recessive?
Example of Pedigree Charts

Dominant or Recessive?
Summary



Pedigrees are family trees that explain your
genetic history.
Pedigrees are used to find out the probability
of a child having a disorder in a particular
family.
To begin to interpret a pedigree, determine if
the disease or condition is autosomal or Xlinked and dominant or recessive.
Pedigree Chart -Cystic Fibrosis
Human Disorders Controlled
by a Single Gene
– Many human traits
• Show simple inheritance patterns.
• Are controlled by genes on autosomes.
Recessive Disorders
– Most
human genetic disorders
are recessive.
Individuals can be carriers of
these diseases.
Figure 9.14
Dominant
Disorders
–
Some human genetic
disorders are dominant.


Achondroplasia is a form
of dwarfism.
Huntington’s disease is
another example of a
dominant disorder
Evolution Connection:
The Telltale Y Chromosome
– Sex
chromosomes
 Influence
the inheritance of certain traits.
 The Y chromosome of human males is only
about one-third the size of the X
chromosome.
 Biologists believe that X and Y were once a
fully homologous pair.
 Major episodes of change have rearranged
pieces of the Y chromosome.
Evolution Connection:
The Telltale Y Chromosome
–
Researchers recently
used comparisons of
Y DNA to confirm that
the Lemba tribe in
Africa descended
from ancient Jewish
people.
Off to the computer lab!!!!
A Tour of
Genetics