Transcript Document

Gregor Mendel
“Father of Genetics”
•Wrote “Experiments in
Plant Hybridization” in 1865
•His work wasn’t discovered
until the next century
Painting of Mendel
Mendel
Table 14.1 The Results of Mendel’s F1 Crosses for Seven Characters in Pea Plants
Sweet Pea Flowers
Alleles, Alternative Versions of a Gene
Homozygous
means
having only one form
of gene or allele
Ex: WW or ww
Heterozygous means a
trait represented by at
least two different alleles,
or forms of a gene
Ex: Ww
In the formation of a
zygote, or fertilized egg,
each parent of an
organism contributes one
form of a
gene or allele, for each
trait in most cases.
In Mendelian Genetics,
dominant traits are
represented by capital
letters; recessive ones
by lower case letters
Dominant traits (genes)
are always expressed if
the gene is present;
recessive traits
are expressed only if the
dominant genes are
absent
For example, widow’s peak
(W) is a dominant trait in
humans.
If the gene for widow’s
peak is present, W, the
person will have widow’s
Peak. (WW, Ww)
Homologous Chromosomes
eye color locus
B = brown eyes
eye color locus
b = blue eyes
This person would
have brown eyes (Bb)
Paternal Maternal
Meiosis - eye color
B
sperm
B
B
Bb
haploid (n)
b
diploid (2n)
b
b
meiosis I
meiosis II
The physical appearance
of an organism is known as
the phenotype; the genetic
makeup (the letters) are
known as the genotype
Ex: Widow’s peak is the pheno
type; Ww is the genotype
The way to show the possible pairings of genes
between two organisms is
called a Punnett Square.
Punnett Square
• A Punnett square is used to
show the possible combinations
of gametes.
Breed the P generation
• tall (TT) vs. dwarf (tt) pea
plants
T
t
t
T
tall (TT) vs. dwarf (tt) pea
plants
T
T
t Tt
Tt
t Tt
Tt
produces the
F1 generation
All Tt = tall
(heterozygous tall)
Breed the F1 generation
•Heterozygous Tall (Tt) pea plants
T
T
t
t
Cross a purebred black
guinea pig and a
purebred brown guinea
pig. Black is dominant
over brown.
B
b
b
Bb
Bb
(Brown)
B
(black)
Bb
Bb
All
offspring
are black
and
heterozy
gous.
If bushy eyebrows (B) are
dominant over fine
eyebrows, (b), show the
cross between one parent
heterozygous for the trait
and one who is
homozygous recessive.
What are the phenotypes
and genotypes of the
offspring?
Answer: Bushy (Bb) 50%
and fine (bb) 50%
Monohybrid Cross
• A breeding experiment that tracks
the inheritance of a single trait.
Dihybrid Cross
•A breeding experiment that tracks
the inheritance of two traits.
Mendel’s “principle of segregation”
a. pairs of genes on homologous
chromosomes separate
during gamete formation (meiosis)
and end up in different gametes.
b. the fusion of gametes at
fertilization pairs genes once again.
Ex: The alleles for height in Mendel’s
pea plants end up in separate
gametes. Tt X Tt could yield four
the offspring: TT, Tt, Tt, tt.
Meiosis - eye color
B
sperm
B
B
Bb
haploid (n)
b
diploid (2n)
b
b
meiosis I
meiosis II
Mendel’s Law of Segregation
• Mendel’s “principle of independent
assortment” (2 different genes)
a. each pair of alleles on
nonhomologous chromosomes
segregates independently of other
pairs during gamete formation
Ex: When Mendel crossed F1 plants
that were heterozygous for
round yellow peas, some F2 plants
did not resemble the parent plants.
Independent Assortment
• How many different gametes
can be produced for the
following allele arrangements?
• Remember: 2n (n = # of
heterozygotes)
1. RrYy
2. AaBbCCDd
3. MmNnOoPPQQRrssTtUu
Answers:
1. RrYy: 2n = 22 = 4 gametes
RY Ry rY ry
2. AaBbCCDd: 2n = 23 = 8 gametes
ABCD ABCd AbCD AbCd
aBCD aBCd abCD abCD
3. MmNnOoPPQQRrssTtUu: 2n = 26
= 64 gametes
Autosomal Inherited
Traits are inherited via
the autosomes (non-sex)
chromosomes. How many
autosomes are in each
of your somatic cells?
That’s right! There are 44
autosomes and 2 sex chromosomes in each of your
somatic (non-sex) cells.
Figure 13.x5 Human male karyotype shown by bright field G-banding of
chromosomes
Autosomal Inherited
Genetic Disorders
include:
•Cystic Fibrosis
•Tay-Sachs Disease
•Sickle Cell Anemia
•Huntington Disease (this
one is dominant!)
Testing a Fetus for Genetic Disorders
Cystic Fibrosis
•Most common inherited
fatal disorder in the U.S.
•Median age of death–37
•One in every 29
Americans has the gene
•Mucus builds up in the
lungs
Francis Collins, current director
of the National Human Genome
Research Institute (NHGRI)
helped pioneer the discovery of
the CF gene in 1989.
Francis
Collins,
discoverer
of the Cystic
Fibrosis
Gene
Former NFL Quarterback, Boomer Esiason and his
son, Gunnar, who has CF.
Diagnosis:
Treatment:
If a man who does not have
Cystic Fibrosis has a sister who
died of CF. He marries a woman
who does not have the disease or
any history of it in her family,
what is the probability that they
will have kids with the disease?
Tay Sachs Disease
a lipid-digesting enzyme is defective
in lysosomes
If two parents are each
carriers of the gene for
Tay-Sachs Disease, what
is the probability of them
having a child with the
disease?
That’s right! They have a
25% chance!
t
T
Tt
T TT
Homozygous
Dominant
t
Tt
Heterozygous
tt
Homozygous
Recessive
Sickle Cell Anemia
The molecular basis of sickle-cell disease: a
point mutation
Huntington Disease
•A degenerative disorder
of the nervous system
•Most people don’t
realize that they have the
disease until after age 30
and may have passed on
the gene
Lake Maracaibo,
Venezuela
Nancy Wexler’s Pedigree of
10,000 people in Lake
Maracaibo
Huntington Disease
(chorea)
•Caused by a stuttering
gene - CAG repeat
•Also called Huntington’s
Chorea
•This is a dominant gene
Some human traits are
sex-linked; that is they
are carried on the X and
Y Chromosomes
For Example:
Hemophilia, Duchenne
Muscular Dystrophy, and
Colorblindness are all traits
carried on the X chromosome
Hemophilia
Duchenne Muscular
Dystrophy
If a female who is carrier
for Duchenne Muscular
Dystrophy (D), what is
the probability of she
and her“normal”husband
having a child with MD?
D
X
Normal
Y
X
X
D
D
d
X
X
D d
X X
D
Carrier Female
D
X
d
Y
X
Y
Male with Disease
A pedigree shows the
genetic relationship
between organisms or
people.
Bloodtypes are also
inherited:
•A = has antigen A
•B = has antigen B
•O =neither
•AB =has both antigens
A and B
Genotypes
O = OO
AB = AB
A = AA or AO
(codominance)
B = BB or BO
(codominance)
Alleles and Genes Interact
to Produce Phenotypes
•Codominance—two alleles of a
gene produce phenotypes that are
both present in the heterozygote.
•Example: ABO blood group
system has three alleles of the
gene: IA, IB, and IO.
ABO Blood Reactions Are
Important in Transfusions
O is the universal
donor (can donate
blood to anyone)
AB is the universal
recipient ( can
receive blood from
anyone)
Patient
Donor
A
B
AB
O
A or O
B or O
anyone
O
•a person who is Rh negative for any
blood type must take only Rh
negative blood
The Rh Factor is also inherited.
Approximately 85% of Americans
are positive for the Rh Factor.
For example, if you have type A
blood and are positive for the Rh
Factor then your bloodtype is A
positive.
So technically there are
8 blood groups:
A positive
A negative
B positive
B negative
AB positive
AB negative
O positive
O negative
In terms of a couple having
kids, positive blood dominates
negative blood.
For example, a father with A
positive blood and his wife
with A negative blood would
have kids with A positive
blood.
RhoGAM
A woman who is pregnant and
is Rh negative and has an Rh
positive child must take
RhoGAM in order to not reject
the child.
If a woman who is
type O and a man
who is type A have
kids, what are their
possible bloodtypes?
WOMAN
A
O
O
AO
AO
MAN
A
AO
AO
A
O
O
AO
OO
O
AO
OO
1) If a brown eyed man marries
a brown eyed woman and they
have a blue eyed child, what
are the genotypes of the
parents?
2) In rabbits, the allele for black coat
color (B) is dominant over the allele
for brown coat color (b). Predict
the results of a cross between a
rabbit homozygous for black coat
color (BB) and a rabbit homozygous
for brown coat color (bb)
3) If two sisters in a family have free
earlobes (F) and their two brothers
have attached earlobes (f), what
genotypes are the parents most
likely to have if neither parent has
attached earlobes?
4) What is the probability of a couple
who are both heterozygous for
widow’s peak (W) and free earlobes
(F) having a child with neither trait?
5) In pea plants, smooth seed texture
is dominant over wrinkled seed
texture. A gardener has a pea
plant that produces smooth seeds.
How can the gardener determine
whether the plant is homozygous
or heterozygous for the allele that
determines seed texture?
6) In pea plants, if purple flowers
are dominant over white, and
smooth seeds are dominant
over wrinkled, predict the outcome of the crossing of a pea
plant heterozygous for color
and homozygous recessive for
seed coat texture with one
heterozygous for both traits.
7) In fruit flies, L = long wings and
l = short wings. When a
long-winged fly is crossed with a
short-winged fly, the offspring
exhibit a 1:1 ratio.
What is the genotype of the
parent flies?
8) In squash an allele for white color
(W) is dominant over yellow (w).
Give the phenotypic ratios for the
results of each of the following
crosses:
a) W/W x w/w
b) W/w x w/w
c) W/w x W/w
9) In humans, pointed eyebrows
(B) are dominant over smooth
eyebrows (b). Mary’s father has
pointed eyebrows, but she and
her mother have smooth. What
is the genotype of the father?
10) In tomatoes, red fruit (R) is
dominantover yellow fruit (r), and
tallness (T) is dominant over
shortness (t). A plant that is RrTT
is crossed with aplant that is rrTt.
What are the chances of an offspring
beingheterozygous for both traits?
11) In fruit flies, gray wings (G) are
dominant to black wings and normal
wing length (N) is dominant to vestigial
(short) wing length. What is the
probability of a gray fly with normal
wings heterozygous for both traits and a
black fly with normal wings, but
homozygous for wing length having
offspring which are
gray and have normal wing lengths?
12) Free ear lobes (F) and widow’s peak
(W) are dominant traits in humans.
What is the probability of a woman who
has attached earlobes and no widow’s
peak and a man who is heterozygous
for both traits having kids who have
attached ear lobes and no widow’s
peak?
Genes A and B are 6 map units
apart, and A and C are 4 map
units apart. Which gene is in the
middle if B and C are 10 map
units apart? Which is in the
middle if B and C are 2 map units
apart?
In the cross RrTt X rrtt,
a. all of the offspring will be
tall with red fruit
b. 75% will be tall with red fruit
c. 50% will be tall with red fruit
d. 25% will be tall with red fruit
In terms of evolution, why is
the incidence of sickle
cell anemia higher among the
African-American population
in the United States?
If one parent has type O blood
and one of the kids is type A,
what are the possible blood
types of the other parent?
If one parent has type AB
blood and the other has A,
what are the possible blood
types of the kids?
For most human traits, how
many alleles does each parent
contribute to the zygote or
fertilized egg?
What is the term used to
describe traits that are inherited
by a number of genes of each
parent?
If you have good notes from yesterday
on Cystic Fibrosis you should be able to:
1) describe at least two organs affected
2) show a Punnett square with the
inheritance pattern
3) list one organization which raises
awareness of CF
4) name and describe the specific
protein affected by CF
5) significance of discovery of the CF
gene
When RhoGAM is given to a
pregnant mother,
what is the Rh status of the
mother, father, and baby?