Transcript 05 Chapter heredity

Table of Contents
Chapter: Heredity
Section 1: Genetics
Section 2: Genetics Since Mendel
Section 3: Biotechnology
Genetics
1
Inheriting Traits
• Eye color, nose shape,
and many other physical
features are some of the
traits that are inherited
from parents.
• An organism is a
collection of traits, all
inherited from its parents.
Genetics
1
Inheriting Traits
• Heredity (huh REH duh
tee) is the passing of
traits from parent to
offspring.
Genetics
1
What is genetics?
• Generally, genes on chromosomes control an
organism’s form and function.
• The different forms of a trait that a gene may
have are called alleles (uh LEELZ).
• When a pair of chromosomes separates
during meiosis (mi OH sus), alleles for each
trait also separate into different sex cells.
Genetics
1
What is genetics?
• Every sex cell has one allele for each trait.
• The study of how traits are inherited through
the interactions of alleles is the science of
genetics (juh NE tihks).
Genetics
1
Mendel—The Father of Genetics
• Gregor Mendel began
experimenting with
garden peas in 1856.
• Mendel made careful
use of scientific
methods, which
resulted in the first
recorded study of how
traits pass from one
generation to the next.
Genetics
1
Mendel——The Father of Genetics
• Mendel was the first to trace one trait through
several generations.
• He was also the first to use the mathematics
of probability to explain heredity.
Genetics
1
Genetics in a Garden
• Each time Mendel studied a trait, he crossed
two plants with different expressions of the
trait and found that the new plants all looked
like one of the two parents.
• He called these new plants hybrids (HI
brudz) because they received different
genetic information, or different alleles, for a
trait from each parent.
Genetics
1
Genetics in a Garden
• An organism that always produces the same
traits generation after generation is called a
purebred.
Genetics
1
Genetics in a Garden
• Tall plants that always produce seeds that
produce tall plants are purebred for the trait
of tall height.
Genetics
1
Dominant and Recessive Factors
• In his experiments, Mendel used pollen from
the flowers of purebred tall plants to pollinate
by hand the flowers of purebred short plants.
• This process is called cross-pollination.
Genetics
1
Dominant and Recessive Factors
• He found that tall plants crossed with short
plants produced seed that produced all tall
plants.
Genetics
1
Dominant and Recessive Factors
• Mendel called the tall form the dominant
(DAH muh nunt) factor because it
dominated, or covered up, the short form.
• He called the
form that seemed
to disappear the
recessive (rih SE
sihv) factor.
Click image to view movie.
Genetics
1
Using Probability to Make Predictions
• Probability is a branch of mathematics that
helps you predict the chance that something
will happen.
Genetics
1
Using Probability to Make Predictions
• Mendel also dealt with probabilities.
• One of the things that made his predictions
accurate was that he worked with large
numbers of plants.
• He studied almost 30,000 pea plants over a
period of eight years.
• By doing so, Mendel increased his chances of
seeing a repeatable pattern.
Genetics
1
Punnett Squares
• How could you predict what the offspring
would look like without making the cross?
• A handy tool used
to predict results
in Mendelian
genetics is the
Punnett (PUH
nut) square.
Click image to view movie.
Genetics
1
Punnett Squares
• In a Punnett
square, letters
represent
dominant and
recessive alleles.
Genetics
1
Punnett Squares
• An uppercase
letter stands for a
dominant allele.
• A lowercase letter
stands for a
recessive allele.
Genetics
1
Punnett Squares
• They show the genotype (JEE nuh tipe), or
genetic makeup, of an organism.
• The way an organism looks and behaves as a
result of its genotype is its phenotype (FEE
nuh tipe).
Genetics
1
Alleles Determine Traits
• Most cells in your body have two alleles for
every trait.
• These alleles are located on chromosomes
within the nucleus of cells.
Genetics
1
Alleles Determine Traits
• An organism with two alleles that are the
same is called homozygous (hoh muh ZI
gus).
• An organism that has two different alleles for
a trait is called heterozygous (he tuh roh ZI
gus).
Genetics
1
Making a Punnett Square
Section Check
1
Question 1
How did Gregor Mendel use his knowledge of
mathematics in his study of heredity in pea
plants?
Section Check
1
Answer
Mendel was the first person to use the
mathematics of probability to explain heredity.
Probability is the branch of mathematics that
helps you predict the chance that something
will happen.
Section Check
1
Question 2
According to this diagram, if meiosis proceeds
correctly, how many alleles of a particular gene
can a female pass on to her offspring?
Section Check
1
Answer
Although she has two alleles of each gene, a
mother can pass only one allele to her
offspring. Meiosis separates alleles so that eggs
have only one allele for each gene. The new
individual then gets one allele from the mother
and the other from the father.
Section Check
1
Question 3
Mendel crossed pea plants that were pure-bred
for yellow seeds with plants that were purebred for green seeds. All the offspring of this
cross had yellow seeds. Based on these results,
which form of color was recessive and which
was dominant?
Section Check
1
Answer
Green seed color was recessive and yellow
seed color was dominant. Mendel called the
form that seemed to disappear (green in this
case) recessive and the form that covered up
(yellow in this case) dominant.
Genetics Since Mendel
2
Incomplete Dominance
• When the offspring of two homozygous
parents show an intermediate phenotype, this
inheritance is called incomplete dominance.
• Examples of
incomplete dominance
include the flower
color of some plant
breeds and the coat
color of some horse
breeds.
Genetics Since Mendel
2
Multiple Alleles
• Many traits are controlled by more than two
alleles.
• A trait that is controlled by more than two
alleles is said to be controlled by multiple
alleles.
Genetics Since Mendel
2
Multiple Alleles
• Traits controlled by multiple alleles produce
more than three phenotypes of that trait.
• Blood type in humans is an example of
multiple alleles that produce only four
phenotypes.
• The alleles for blood types are called A, B,
and O.
Genetics Since Mendel
2
Multiple Alleles
• When a person inherits
one A allele and one B
allele for blood type,
both are
expressedphenotype
AB.
• A person with
phenotype A blood has
the genetic makeup, or
genotypeAA or AO.
Genetics Since Mendel
2
Multiple Alleles
• Someone with
phenotype B blood
has the genotype BB
or BO.
• Finally, a person with
phenotype O blood has
the genotype OO.
Genetics Since Mendel
2
Polygenic Inheritance
• Polygenic (pah lih JEH nihk) inheritance
occurs when a group of gene pairs acts
together to produce a trait.
• The effects of
many alleles
produces a wide
variety of
phenotypes.
Click image to view movie.
Genetics Since Mendel
2
Polygenic Inheritance
• Your height and the color of your eyes and
skin are just some of the many human traits
controlled by polygenic inheritance.
• It is estimated that three to six gene pairs
control your skin color.
• The environment also
plays an important
role in the expression
of traits controlled by
polygenic inheritance.
Genetics Since Mendel
2
Impact of the Environment
• Your environment plays a role in how some
of your genes are expressed or whether they
are expressed at all.
• Environmental influences can be internal or
external.
Genetics Since Mendel
2
Impact of the Environment
• Although genes determine many of your
traits, you might be able to influence their
expression by the decisions you make.
• 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.
Genetics Since Mendel
2
Human Genes and Mutations
• Occasionally errors occur in the DNA when it
is copied inside of a cell.
• Such changes and errors are called mutations.
• Not all mutations are harmful. They might
be helpful or have no effect on an organism.
Genetics Since Mendel
2
Chromosome Disorders
• Every organism has a specific number of
chromosomes.
• However, mistakes in the process of meiosis
can result in a new organism with more or
fewer chromosomes than normal.
Genetics Since Mendel
2
Chromosome Disorders
• If three copies of chromosome 21 are
produced in the fertilized human egg,
Down’s syndrome results.
• Individuals with Down’s syndrome can be
short, exhibit learning disabilities, and have
heart problems.
Genetics Since Mendel
2
Recessive Genetic Disorders
• Many human genetic disorders, such as cystic
fibrosis, are caused by recessive genes.
• Some recessive genes are the result of a
mutation within the gene.
• Many of these alleles are rare.
Genetics Since Mendel
2
Recessive Genetic Disorders
• Such genetic disorders occur when both
parents have a recessive allele responsible
for this disorder.
• Because the parents are heterozygous, they
don’t show any symptoms.
Genetics Since Mendel
2
Recessive Genetic Disorders
• If each parent passes the recessive allele to
the child, the child inherits both recessive
alleles and will have a recessive genetic
disorder.
Genetics Since Mendel
2
Recessive Genetic Disorders
• Cystic fibrosis is the most common genetic
disorder that can lead to death among
Caucasian Americans.
• In most people, a thin fluid is produced that
lubricates the lungs and intestinal tract.
• People with cystic fibrosis produce thick
mucus instead of this thin fluid.
Genetics Since Mendel
2
Recessive Genetic Disorders
• The thick mucus builds up in the lungs and
makes it hard to breathe.
• This buildup often results in repeated
bacterial respiratory infections.
Genetics Since Mendel
2
Sex Determination
• Each egg produced by a female normally
contains one X chromosome.
• Males produce sperm that normally have
either an X or a Y chromosome.
Genetics Since Mendel
2
Sex Determination
• When a sperm with an X chromosome
fertilizes an egg, the offspring is a female,
XX.
• A male offspring, XY is the result of a Ycontaining sperm fertilizing an egg.
Genetics Since Mendel
2
Sex-Linked Disorders
• An allele inherited on a sex chromosome is
called a sex-linked gene.
• Color blindness is a
sex-linked disorder
in which people
cannot distinguish
between certain
colors, particularly
red and green.
Genetics Since Mendel
2
Sex-Linked Disorders
• This trait is a recessive allele on the X
chromosome.
• Because males have only one X
chromosome, a male with this allele on
his X chromosome is color-blind.
• A color-blind female occurs only when
both of her X chromosomes have the allele
for this trait.
Genetics Since Mendel
2
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.
Genetics Since Mendel
2
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.
Genetics Since Mendel
2
Using Pedigrees
• A pedigree is a useful tool for a geneticist.
• 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
2
Using Pedigrees
• Pedigrees also are important in breeding
animals or plants.
• These organisms are bred to increase their
yield and
nutritional
content.
Section Check
2
Question 1
Why is color blindness a sex-linked trait?
Section Check
2
Answer
This trait is sex-linked because the alleles for
this trait are carried on the X-chromosome, one
of the sex chromosomes. Color-blindness is
caused by a recessive allele and because males
get only one X-chromosome, they are more
likely to be color-blind 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
Answer
The correct answer is C. The alleles for dark
fur color are controlled by the internal
temperature of the rabbits. These alleles are
expressed only at lower temperatures.
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
2
Answer
The correct answer is C. Down’s syndrome
occurs when there are three copies of
chromosome 21 instead of the usual two.
Biotechnology
3
Genetic Engineering
• Through genetic engineering, scientists are
experimenting with biological and chemical
methods to change the arrangement of DNA
that makes up a gene.
• Genetic engineering already is used to help
produce large volumes of medicine.
Biotechnology
3
Recombinant DNA
• Recombinant DNA is made by inserting a
useful segment of DNA from one organism
into a bacterium.
• This method is
used to produce
human insulin,
human growth
hormone, and
other chemicals
by bacteria.
Biotechnology
3
Gene Therapy
• In gene therapy, a normal allele is placed in a
virus.
• The virus then
delivers the normal
allele when it infects
its target cell.
• The normal allele
replaces the
defective one.
Biotechnology
3
Gene Therapy
• Scientists are conducting experiments that
use this method to test ways of controlling
cystic fibrosis and some kinds of cancer.
• Gene therapy might be a method of curing
several other genetic disorders in the future.
Biotechnology
3
Genetically Engineered Plants
• Selecting plants with the most desired traits
to breed for the next generation is called
selective breeding.
• Recent advances in genetics have not
replaced selective breeding.
Biotechnology
3
Genetically Engineered Plants
• Genetic engineering can produce
improvements in crop plants, such as
corn, wheat, and rice.
• 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
3
Question 1
What is it called when scientists use
biological and chemical methods to change
the arrangement of DNA in a gene?
Section Check
3
Answer
This is called genetic engineering. This
process has been used to make large volumes
of medicines and research is being conducted
to find many other ways to use these
techniques.
Section Check
3
Question 2
What does this diagram illustrate?
Section Check
3
A. Bacteria cells can produce human insulin.
B. Bacteria genes are put in human cells.
Section Check
3
C. People with diabetes are given the gene for
insulin.
D. The insulin gene is inserted in people with
diabetes.
Section Check
3
Answer
The correct answer is A. Genetic engineering
can be used to insert the human gene for insulin
into bacterial cells. The bacterial cells then
produce human insulin. This insulin can be
used to treat people who have diabetes.
Section Check
3
Question 3
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
Section Check
3
Answer
The correct answer is A. Often; a virus is used
to deliver the normal allele to the patient.
Scientists have been conducting experiments to
cure many different genetic diseases, including
cystic fibrosis, in this way.
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