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Table of Contents
Chapter: Heredity
Section 1: Genetics
Section 2: Genetics Since Mendel
Section 3: Biotechnology
Genetics
1
Inheriting Traits
• Traits are
inherited
from parents
• Heredity - the
passing of traits
from parent to
offspring.
Genetics
1
What is genetics?
• Alleles - different
forms of a trait
that a gene may
have
• Alleles for each
trait separate
into different
sex cells during
meiosis
Genetics
1
What is genetics?
• Genetics - study of how traits are inherited
Genetics
1
Mendel—The Father of Genetics
• Mendel (1856) –
studied genes of pea
plants
• First to:
• trace one trait
through several
generations
• use probability to
explain heredity
Genetics
1
• Purebred - always produces the same
traits generation after generation
• Hybrids – receive different alleles for a trait
from each parent
Genetics
1
Dominant and Recessive Factors
• Cross-pollination - using pollen from one
flower to pollinate others
Genetics
1
Dominant and Recessive Factors
• Dominant - factor expressed if there is only
one allele for the trait
• Recessive –
factor expressed
only when there
are 2 alleles for
the trait
Click image to view movie.
Genetics
1
Punnett Squares
• Studied > 30,000 pea plants over 8 yrs
• Punnett square tool used to
predict results
Click image to view movie.
Genetics
1
Punnett Squares
• Uppercase dominant allele
• Lowercase recessive allele
Genetics
1
• Genotype - genetic makeup
• Phenotype - way an organism looks and
behaves
Genetics
• Homozygous - two alleles that are the
same
• Heterozygous - two different alleles for a trait
1
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
• Incomplete dominance – results in an
intermediate phenotype
Genetics Since Mendel
2
• Multiple alleles trait that is
controlled by more
than two alleles
• Produce more
than three
phenotypes
Genetics Since Mendel
2
Multiple Alleles
• Alleles for blood
types
• A, B, and O.
Genetics Since Mendel
2
Polygenic Inheritance
• Polygenic inheritance - a group of gene
pairs acts together to produce a trait.
• Produces a wide
variety of
phenotypes.
Click image to view movie.
Genetics Since Mendel
2
Polygenic Inheritance
• Examples:
• Height
• Eye color
• Skin
color
Genetics Since Mendel
2
Impact of the Environment
• Environment
plays a role in
how some
genes are
expressed
Genetics Since Mendel
2
Human Genes and Mutations
• Mutations – errors when DNA copies
• Can be harmful or helpful
Genetics Since Mendel
2
• Chromosome Disorders - error in the
number of chromosomes
Genetics Since Mendel
2
Recessive Genetic Disorders - caused by
recessive genes.
Genetics Since Mendel
2
Sex Determination
• Egg - 1 X
chromosome
• Sperm - 1 X or 1
Y chromosome
• Male XY
• Female XX
Genetics Since Mendel
2
Sex-Linked Disorders
• Sex-linked
gene - allele
inherited on a
sex
chromosome
• Color blindness is
sex-linked
Genetics Since Mendel
2
Pedigrees Trace Traits
• Pedigree visual tool for
following a
trait through
generations
• Males –
squares
• Females –
circles
Genetics Since Mendel
2
Pedigrees Trace Traits
• Filled circle
or square shows trait
• Half-colored carriers
• Empty - do not
have the trait
and are not
carriers.
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 scientists are
experimenting
to change the
arrangement of
DNA that makes
up a gene.
Biotechnology
3
• Recombinant DNA - made by inserting a
useful segment of DNA from one organism
into a bacterium.
• Used to produce
• human
insulin,
• human
growth
hormone
Biotechnology
3
Gene Therapy
• Normal allele is
placed in a virus.
• The virus then
delivers the normal
allele and replaces
the defective one
Biotechnology
3
Genetically Engineered Plants
• Selective breeding - selecting plants with the
most desired traits to breed
Biotechnology
3
Genetically Engineered Plants
• Find genes that
produce desired
traits in one plant
and then insert
them 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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