Transcript trait - Plain Local Schools

10.1 Genetics developed from
curiosity about inheritance
I. The Blending Hypothesis of
Inheritance
A. A trait is a variation of a particular
characteristic such as for red flowers or
yellow flowers
B. In the early 1800’s many biologists
believed in the blending hypothesis,
which stated that offspring would be a
blend of their parents traits. A red and
yellow flower would produce and orange
flower
II. Mendel’s Plant Breeding
Experiments
A. Mendel’s work gave rise to the
branch of Biology called genetics,
the study of heredity
B. Mendel developed the particulate
hypothesis which states that parents
pass on separate and distinct factors,
or genes
Mendel’s Plant Breeding
Experiments
C. To test this hypothesis, Mendel
crossed true-breeding plants that
had distinct and contrasting traits
such as purple and white flowers
D. Mendel cross-fertilized all his
pea plants by hand to control
which traits he wanted to control
Mendel methods
10.2 Mendel’s Principle of
Segregation
I. Mendel’s Principle of
Segregation
A. The offspring of two different
true-breeding varieties are called
hybrids
B. When Mendel crossed plants that
differed in only one-trait it was
called a mono-hybrid cross
C. From these results Mendel
developed the following hypothesis
1. There are alternative forms of a gene
called alleles.
2. For each inherited trait, an organism has
two alleles for the gene controlling that
character, one from each parent. If both
alleles are the same the individual is
homozygous, and if the alleles are
different the individual is heterozygous.
Mendel developed the following
hypothesis
3. When only one of the alleles in a
heterozygous individual appears to
affect the trait, that allele is called
the dominant trait. The allele that
does not appear to have an affect
on the individual is called the
recessive trait
Mendel’s Observation
Mendel’s Observations
Mendel developed the following
hypothesis
4. The two alleles for a character
separate during the formation of
gametes, so each gamete carries
only one allele for each character.
This is known as Mendel’s
Principle of Segregation
II. Probability and Punnett
Squares
A. The inheritance of alleles follows the
laws of probability
B. If you were to flip two pennies the
probability of flipping a head or a
tail on one does not affect the
probability of the other one
C. A diagram that shows all the
possible outcomes of a genetic cross
is the Punnett Square
Probability and Punnett
Punnett Square
Eye color
Homozygous
Brown male X
Homozygous
Blue female
B
B
b
Bb
Bb
b
Bb
Bb
III. Genotypes and Phenotypes
A. The way an organism looks is
not the same as its genetic makeup
B. An observable trait is called a
phenotype while the genetic
make-up of alleles is called the
genotype
IV. The Testcross
A. A testcross breeds individuals of
unknown genotypes, but the
dominant phenotype with a
homozygous recessive individual
B. Depending on the ratios of the
offspring, the genotype of the
unknown can be determined
Testcross
V. Mendel’s Principle of
Independent Assortment
A. Mendel also did crosses between plants
that differed in two traits called a
dihybrid cross
B. From this he developed his Law of
Independent Assortment which states
that during gamete formation the way in
which one allele is inherited does not
affect the way another is inherited if they
are on separate chromosomes
Independent Assortment
Problem: Monohybrid 1
• 1. An allele for brown eyes B is
dominant over that for blue eyes b. A
blue-eyed man, both of whose parents
were brown-eyed, marries a woman.
They have one child who is blue-eyed.
What are the genotypes of all the
individuals mentioned?
Problem 1
Man’s parents: Bb
Dad: bb
Mom: Bb
Kids: Bb or bb
b
b
B
Bb
Bb
b
bb
bb
Problem: Monohybrid 2
2. The ability to taste the chemical PTC
is determined by a single gene in
humans with the ability to taste given
by the dominant allele T and inability
to taste by the recessive allele
t. Suppose two heterozygous tasters
(Tt) have a large family.
Problem: Monohybrid 2
a.
b.
c.
Predict the proportion of their children who
will be tasters and nontasters. Use a Punnett
square to illustrate how you make these
predictions.
What is the likelihood that their first child
will be a taster? What is the likelihood that
their fourth child will be a taster?
What is the likelihood that the first three
children of this couple will be nontasters?
Problem 2
a. 3:1
b. 3/4, 3/4
c. 1/64
T
t
T
TT
Tt
t
Tt
tt
Dihybrid Cross
Dihybrid Cross- FOIL
First
Outside
Inside
Last
RrYy x RrYy
Problem 3: Dihybrid
3. In pepper plants, green (G) fruit
color is dominant to red (g) and
round (R) fruit shape is dominant
to square (r) fruit shape. These
two genes are located on different
chromosomes.
3. Dihybrid
a. What gamete types will be
produced by a heterozygous green,
round plant?
b. If two such heterozygous plants
are crossed, what genotypes and
phenotypes will be seen in the
offspring and in what proportions?
#3 Types of gametes
FOIL
First- GR
Outside- Gr
Inside- gR
Last- gr
Dihybrid: Pepper Plants
GR
Gr
gR
gr
GR
GGRR GGRr
GgRR
GgRr
Gr
GGRr
GGrr
GgRr
Ggrr
gR
GgRR
GgRr
ggRR
ggRr
gr
GgRr
Ggrr
ggRr
ggrr
Pepper Plants
9 Green, round
3 Green, square
3 Red, round
1 Red, square
1 GGRR 2 GgRR 1 ggRR
2 GGRr
4 GgRr
2 ggRr
1 GGrr
2 Ggrr
1 ggrr
10.3 There are many variations of
inheritance patterns
I. Intermediate Inheritance
A. When an organism has two
alleles and neither is dominant
the phenotype is intermediate
between the two alleles
B. This pattern of inheritance is
called intermediate inheritance
Intermediate Example
Problem: Intermediate
Inheritance
4. A hybrid pink CRCW snapdragon
was crossed with a pure white one
CWCW. Red flower color is
incompletely dominant.
• Make a diagram and list the
genotypic and phenotypic ratios of
the F1 generation
Problem 4
1:1
CR CW :CW CW
Pink:White
CR
CW
CW
CR CW C W CW
CW
CR CW C W CW
II. Multiple Alleles
A. Many genes have several alleles
for each trait which expands the
number of genotypes and
phenotypes
B. Codominance is when a
heterozygous individual
expresses both traits equally.
Multiple Allele Example
Problem: Multiple Alleles
5. Paul is blood type O. His father was
blood type A and his mother was blood
type B. What were the genotypes of his
parents and what are the possible blood
types and ratios expected for crosses
involving these parental genotypes?
Problem 5
IAi
IA
IBi
and
1:1:1:1
AB:A:B:O
i
IB
IA IB IBi
i
IAi
ii
III. Polygenic Inheritance
A. When multiple genes affect a character
the variation in phenotypes can become
even greater.
B. When two or more genes affect a single
character, it is called polygenic
inheritance
C. Examples of polygenic inheritance would
include skin color, and height
Problem: Polygenic
• 6. Melanin is coded for when the
gene L, M, or N is present. The
more of these genes are present,
then the darker the skin the
individual. Number the following
genotypes in order of the darkest to
lightest skin color phenotypes.
Problem 6
#1 LLMMNN
#5 LXMXXX
#2 LLMXNN
#5 XXMMXX
#4 LXMMXX
#3 LXMMNX
1= Darkest 6=Lightest
IV. The Importance of
Environment
A. An individuals phenotype
depends on environment as well
as on gene
B. In humans, nutrition influences
height, exercise affects build,
and exposure to sunlight darkens
the skin
10.4 Meiosis Explains Mendel’s
principles
I. Chromosome Theory of
Inheritance
A. Biologists worked out the
processes of mitosis and meiosis in
the late 1800s and observed the
parallels between the behavior of
chromosomes and the behavior of
Mendel’s heritable factors
Chromosome Theory
B. The chromosome theory of
inheritance states that genes are
located on chromosomes, and the
behavior of chromosomes during
meiosis and fertilization accounts for
inheritance patterns
C. The alleles for a gene reside at the
same location or gene locus
Pea
Plant
II. Genetic Linkage and Crossing
Over
A. Mendel’s principles only work when
for genes that are located on separate
chromosomes
B. The tendency for the alleles on one
chromosome to be inherited together
is called genetic linkage
C. The closer the two genes are on a
chromosome, the greater the genetic
linkage
Linkage
10.5 Sex-linked traits have
unique inheritance patterns
I. Sex-linked Genes
A. Many species have sex
chromosomes, designated X and Y
that are associated with
determining an individual’s sex
XX= Female, while XY= Male
Sex-linked genes
B. Any gene located on a sex
chromosome is called a sex-linked
gene
C. Sex-linked genes were
discovered by Thomas Hunt
Morgan while studying fruit flies
Sex-linked eye color
II. Sex-Linked Disorders
A. A number of human conditions,
including red-green color blindness
and hemophilia are inherited as sex
linked recessive traits
B. It takes two copies of the allele to
be present in females for them to show
signs of the disorder while it only takes
one in males
Problem: Sex-linked
7. A color blind father and a mother
who carries the color blind trait (b)
have a boy and a girl. What are the
percent chances of the children
being color blind? A carrier for
color blindness?
Color blindness: Sex-linked
50% color blind
children
25% carrier
Xb
Y
XB
XB Xb XBY
Xb
Xb Xb
XbY
12.2 Accidents Affecting
Chromosomes can Cause
Disorders
I. Down Syndrome
A. Trisomy 21 results in having three
number 21 chromosomes
B. In most cases, a human embryo
with an abnormal number of
chromosomes results in a miscarriage
C. People with trisomy 21 have Down
syndrome, named after John Langdon
Down
II. Nonseparation of
Chromosomes
A. Nondisjunction is when
homologous fail to separate
B. A woman’s age will have an effect
on the possibility of nondisjunction
occurring
C. This is due to the time line of egg
cell development
Nondisjunction
III. Damaged Chromosomes
A. Duplication is when part of a
chromosome is repeated
B. Deletion is when a fragment of a
chromosome is lost
C. Inversion involves reversing a
fragment of the original chromosome
D. Translocation occurs when a
fragment of one chromosome attaches
to a non-homologous chromosome
Damaged Chromosomes
Problem 8
1. ABCDEFGDEF
G  HIJK
2. PQRSTUV
 HIJK
3. ABCGFED  HIJK
4. PQRST  W Y Z
Problem 8: Damaged
Chromosomes
1. ABCDEFGDEF
G  HIJK
1. D upli cat ion
2. PQRSTUV
 HIJK
2. Tra nslocat ion
3. ABCGFED
 HIJK
3. I nvers ion
4. PQRST  W Y Z
4. De let ion
IV. Jumping Genes
A. Single genes may move from one
location to another in a chromosome or
to a different chromosome
B. This was discovered by Barbara
McClintock in the 1940’s
C. These genes can land in the middle
of other genes and disrupt them
D. These genes are called transposons
Transposons
12.3 Mendel’s Principles Apply to
Humans
I. Working With Human
Pedigrees
• A. Human geneticists cannot
control matings, but must analyze
the patterns of existing families
• B. A pedigree is a family tree that
records and traces traits
Pedigree Symbols
II. Disorders Inherited as
Recessive Traits
A. There are over one thousand genetic
disorders that are inherited as a
dominant or recessive trait controlled
by a single gene
B. Most human genetic disorders are
recessive
C. A carrier is an individual who has
a copy of the recessive disorder but
does not show symptoms
Attached Earlobes
Pedigree #9
a. Is the attached ear lobe trait a
dominant or recessive trait? How do
you know?
Recesssive, only those ff colored.
b. What two terms could be used to
describe the Ff genotype?
Heterozygous, or carrier
Problem 9: Pedigree
What are the percent
chances?
25% FF 50% Ff
25% ff
75% Unattached
25% attached
F
f
F
FF Ff
f
Ff
ff
III. Disorders inherited as
Dominant Traits
A. Dominant alleles that are lethal
are more common than lethal
recessives
B. Usually, the person with the
dominant disorder dies before the
allele can be passed on
Huntington’s Disease
IV. Sex-Linked Disorders
A. Sex-Linked alleles are usually
located on the X Chromosome in
humans
B. A male only needs to inherit one
copy of the allele to exhibit the trait
C. A female must inherit two copies of
the allele to exhibit the trait
Colorblindness
Deaf Pedigree
Draw a pedigree
for the punnett
square.
Children: 2
older boys are
deaf. 2 younger
girls are
carriers.
Deaf Pedigree
V. Predicting and Treating
Genetic Disorders
A. A genetic counselor is trained to
collect and analyze data about
inheritance patterns
B. This information is used by couples
to determine the risks of passing on
genetic disorders to their children
C. Genetic tests are done before and
after the baby is born