Transcript Genetics Since Mendel A. Incomplete Dominance

Table of Contents
Chapter: Heredity
Section 1: Genetics
Section 2: Genetics Since Mendel
Genetics Since Mendel
2
A. Incomplete Dominance
1. When the offspring of two homozygous
parents show an intermediate phenotype, this
inheritance is called incomplete dominance.
2. Examples of
incomplete dominance
include the flower
color of some plant
breeds and the coat
color of some horse
breeds.
Genetics Since Mendel
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B. Multiple Alleles
1. Many traits are controlled by more than two
alleles.
2. A trait that is controlled by more than two
alleles is said to be controlled by multiple
alleles.
Genetics Since Mendel
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B. Multiple Alleles
3. Traits controlled by multiple alleles produce
more than three phenotypes of that trait.
4. Blood type in humans is an example of
multiple alleles that produce only four
phenotypes.
5. The alleles for blood types are called A, B,
and O.
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B. Multiple Alleles
6. When a person inherits
one A allele and one B
allele for blood type,
both are
expressedphenotype
AB.
7. A person with
phenotype A blood has
the genetic makeup, or
genotypeAA or AO.
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B. Multiple Alleles
8. Someone with
phenotype B blood
has the genotype BB
or BO.
9. Finally, a person with
phenotype O blood has
the genotype OO.
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C. Polygenic Inheritance
1. Polygenic (pah lih JEH nihk) inheritance
occurs when a group of gene pairs acts
together to produce a trait.
2. The effects of
many alleles
produces a wide
variety of
phenotypes.
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C. Polygenic Inheritance
3. Your height and the color of your eyes and
skin are just some of the many human traits
controlled by polygenic inheritance.
4. It is estimated that three to six gene pairs
control your skin color.
5. The environment also
plays an important
role in the expression
of traits controlled by
polygenic inheritance.
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D. Impact of the Environment
1. Your environment plays a role in how some
of your genes are expressed or whether they
are expressed at all.
2. Environmental influences can be internal or
external.
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D. Impact of the Environment
3. Although genes determine many of your
traits, you might be able to influence their
expression by the decisions you make.
4. For instance, if some people at risk for skin
cancer limit their exposure to the Sun and
take care of their skin, they might never
develop cancer.
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E. Human Genes and Mutations
1. Occasionally errors occur in the DNA when
it is copied inside of a cell.
2. Such changes and errors are called
mutations.
3. Not all mutations are harmful. They might
be helpful or have no effect on an organism.
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F. Chromosome Disorders
1. Every organism has a specific number of
chromosomes.
2. However, mistakes in the process of meiosis
can result in a new organism with more or
fewer chromosomes than normal.
Genetics Since Mendel
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F. Chromosome Disorders
3. If three copies of chromosome 21 are
produced in the fertilized human egg,
Down’s syndrome results.
4. Individuals with Down’s syndrome can be
short, exhibit learning disabilities, and have
heart problems.
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G. Recessive Genetic Disorders
1. Many human genetic disorders, such as
cystic fibrosis, are caused by recessive genes.
2. Some recessive genes are the result of a
mutation within the gene.
3. Many of these alleles are rare.
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G. Recessive Genetic Disorders
4. Such genetic disorders occur when both
parents have a recessive allele responsible
for this disorder.
5. Because the parents are heterozygous, they
don’t show any symptoms.
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G. Recessive Genetic Disorders
6. If each parent passes the recessive allele to
the child, the child inherits both recessive
alleles and will have a recessive genetic
disorder.
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G. Recessive Genetic Disorders
7. Cystic fibrosis is the most common genetic
disorder that can lead to death among
Caucasian Americans.
8. In most people, a thin fluid is produced that
lubricates the lungs and intestinal tract.
9. People with cystic fibrosis produce thick
mucus instead of this thin fluid.
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G. Recessive Genetic Disorders
10. The thick mucus builds up in the lungs and
makes it hard to breathe.
11. This buildup often results in repeated
bacterial respiratory infections.
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H. Sex Determination
1. Each egg produced by a female normally
contains one X chromosome.
2. Males produce sperm that normally have
either an X or a Y chromosome.
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H. Sex Determination
3. When a sperm with an X chromosome
fertilizes an egg, the offspring is a female,
XX.
4. A male offspring, XY is the result of a Ycontaining sperm fertilizing an egg.
Genetics Since Mendel
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I. Sex-Linked Disorders
1. An allele inherited on a sex chromosome is
called a sex-linked gene.
2. Color blindness is a
sex-linked disorder
in which people
cannot distinguish
between certain
colors, particularly
red and green.
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I. Sex-Linked Disorders
3. This trait is a recessive allele on the X
chromosome.
4. Because males have only one X
chromosome, a male with this allele on
his X chromosome is color-blind.
5. A color-blind female occurs only when
both of her X chromosomes have the allele
for this trait.
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J. Pedigrees Trace Traits
• A pedigree is a visual tool for following a
trait through generations of a family.
• Males are
represented
by squares
and females
by circles.
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J. Pedigrees Trace Traits
• A completely filled circle or square shows
that the trait is seen in that person.
• Half-colored circles or squares indicate
carriers.
• People
represented by
empty circles or
squares do not
have the trait and
are not carriers.
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K. Using Pedigrees
1. A pedigree is a useful tool for a geneticist.
2. When geneticists understand how a trait is
inherited, they can predict the probability that
a baby will be born with a specific trait.
Genetics Since Mendel
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K. Using Pedigrees
3. Pedigrees also are important in breeding
animals or plants.
4. These organisms are bred to increase their
yield and
nutritional
content.
Biotechnology
3
L. Genetic Engineering
1. Genetic engineering, is the use of
biological and chemical methods to change
the arrangement of DNA that makes up a
gene.
2. Genetic engineering already is used to help
produce large volumes of medicine.
3. Genetic engineering researchers are also
looking for new ways improve crop
production and quality.
Biotechnology
3
M. Recombinant DNA
1. Recombinant DNA is made by inserting a
useful segment of DNA from one organism
into a bacterium.
2.This method is
used to produce
human insulin,
human growth
hormone, and
other chemicals
by bacteria.
Biotechnology
3
N. Gene Therapy
1. Gene therapy is another kind of genetic
engineering.
2. In gene therapy, a
normal allele is placed in
a virus. The virus then
delivers the normal allele
when it infects the target
cell. The normal allele
replaces the abnormal
one.
Biotechnology
3
N. Gene Therapy
3. Scientists are conducting experiments that
use this method to test ways of controlling
cystic fibrosis and some kinds of cancer.
4. Gene therapy might be a method of curing
several other genetic disorders in the future.
Biotechnology
3
O. Genetically Engineered Plants
1. Selecting plants with the most desired traits
to breed for the next generation is called
selective breeding.
2. Genetic engineering can produce
improvements in crop plants, such as corn,
wheat, and rice.
Biotechnology
3
O. Genetically Engineered Plants
3. One type of genetic
engineering involves
finding the genes that
produce desired traits
in one plant and then
inserting those genes
into a different plant.
Section Check
2
Question 1
Why is color blindness a sex-linked trait?
A.Because the alleles for this trait are carried
on the X-chromosome, one of the sex
chromosomes.
B.Because it pass through mother side only.
C.Because males are more likely to be colorblind than females.
Section Check
2
Question 2
In Himalayan rabbits, dark-colored fur is only
found on cooler parts of the rabbits’ bodies.
This is an example of _______.
A. how sex-linked conditions change coat color
B. the risk of cancer in rabbits with light fur
C. the impact of internal environment on gene
expression
D. what hybrid rabbits look like
Section Check
2
Question 3
If an individual has three copies of
chromosome 21, what condition will result?
A. color blindness
B. cystic fibrosis
C. Down’s syndrome
D. Hemophilia
Section Check
3
Question 4
What is it called when scientists use
biological and chemical methods to change
the arrangement of DNA in a gene?
Section Check
3
Question 5
Using genetic engineering to replace defective
alleles in people with genetic diseases is called
_______.
A. gene therapy
B. Mendelian genetics
C. pedigree analysis
D. recombinant DNA
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