Transcript chapter 12 powerpoint notes

Chapter 12
Inheritance Patterns &
Human Genetics
Developed By:
R. LeBlanc
Biology Teacher
Mountain Pointe High School
11/’06
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Chapter 12
Inheritance Patterns & Human
Genetics
Francis Collins and his lab group discovered
the gene responsible for cystic fibrosis (CF).
In this chapter, you will learn how diseases,
such as CF, and characteristics, such as eye
color, are inherited and expressed.
Cystic fibrosis (CF) is the most common fatal genetic disease in the US today. It causes the
body to produce a thick, sticky mucus that clogs the lungs, leading to infection, and blocks the
pancreas, stopping digestive enzymes from reaching the intestines where they are required to
digest food.
CF is caused by a defective gene, which codes for a sodium and chloride (salt) transporter
found on the surface of the epithelial cells that line the lungs and other organs. Several
hundred mutations have been found in this gene, all of which result in defective transport of
sodium and chloride by epithelial cells. The severity of the disease symptoms of CF is directly
related to the characteristic effects of the particular mutation(s) that have been inherited by the
sufferer.
CF research has accelerated sharply since the discovery of CFTR in 1989. In 1990, scientists
successfully cloned the normal gene and added it to CF cells in the laboratory, which
corrected the defective sodium chloride transport mechanism. This technique - gene therapy was then tried on a limited number of CF patients. However this treatment may not be as
successful as originally hoped. Further research will be required before gene therapy, and
other experimental treatments, prove useful in combating CF.
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Cystic Fibrosis
• What do you
notice about
the airway of
a normal
person with
one with
cystic
fibrosis?
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Chapter 12
Section 1 Chromosomes
and Inheritance
Chromosomes
•How many chromosomes
does a human cell have?
• Genes reside on
chromosomes.
23 pairs or 46
•How many chromosomes
does a sex cell have?
23
•What are genes?
Genes are short segments
of DNA that contains the
instructions for a single
trait.
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Chapter 12
Section 1 Chromosomes
and Inheritance
Karyotypes: Male and Female
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Chapter 12
Inheritance Patterns
and Human Genetics
Table of Contents
Section 1 Chromosomes and Inheritance
Section 2 Human Genetics
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Chapter 12
Section 1 Chromosomes
and Inheritance
Objectives
• Distinguish between sex chromosomes and autosomes.
• Explain the role of sex chromosomes in sex determination.
• Describe how an X- or Y-linked gene affects the inheritance
of traits.
• Explain the effect of crossing-over on the inheritance of
genes in linkage groups.
• Distinguish between chromosome mutations and gene
mutations.
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Chapter 12
Section 1 Chromosomes
and Inheritance
Chromosomes, continued
• Sex Chromosomes and
Autosomes
– Sex chromosomes
contain genes that
determine an organism’s
sex (gender).
– The remaining
chromosomes that are
not directly involved in
determining the sex of an
individual are called
autosomes.
•
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•What is wrong with the
karyotyping above?
•What should it be?
•This causes birth defects
and is known as Trisomy 13.
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Chapter 12
Section 1 Chromosomes
and Inheritance
Chromosomes, continued
• Sex Determination
– In mammals, an individual carrying two X
chromosomes is female.
– An individual carrying an X and a Y
chromosome is male.
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Chapter 12
Sex Determination; con’t
• In humans there are 22 pairs
of autosome (exact)
chromosomes
• The 23rd pair are the sex
X
chromosomes.
• Indicated by the letters X
Y
and Y.
• Ex. Female = XX
Male = XY
X
X
XX
XX
Female Female
XY
Male
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XY
Male
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Chapter 12
Section 1 Chromosomes
and Inheritance
Effects of Gene Location
• Sex-Linked Genes and Traits
– Genes found on the X chromosome are Xlinked genes.
– A sex-linked trait is a trait whose allele is
located on a sex chromosome.
– Because males have only one X chromosome,
a male who carries a recessive allele on the X
chromosome will exhibit the sex-linked trait.
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Chapter 12
Sex Linked Traits; con’t
• Examples:
– Eye color in fruit flies
– Hemophilia in humans - Unable to clot blood
(recessive trait on the X chromosome)
– Color Blindness in humans - Unable to see red
and green
– PROBLEM: If a man with hemophilia married and
his wife was a carrier of hemophilia, what would
the probability of their children of having this
disease? Just the male child? Female child?
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Chapter 12
Example of Sex-Linked Crosses
H = Normal blood
clotting
XH
Xh
h = hemophiliac
Xh
XHXh
XhXh
Female
Carrier
Female
Hemophiliac
XhY = Male Hemophiliac
XhY
XHY
Y
Male
Normal
Male
Hemophiliac
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Chapter 12
Sex Linked Traits; con’t
• People with red-green color
blindness can not differentiate
between these two colors
• Color blindness is also a X
Linked Trait that is recessive.
• PROBLEM: A mother who
carries the trait for color
blindness wants to know what
the probability would be that
her children would be color
blind if her husband has
normal vision?
R = Normal vision
r = color blindness
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Chapter 12
Sex Linked Traits; con’t
Color blindness solution
•25% chance in all her
children.
Female Carrier
XR
Xr
•50% chance that a male
will be color blind..
•0% chance female will
XR XR XR XR Xr
be, but 50% chance they
will be a carrier.
Y
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XR Y Xr Y
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Chapter 12
Section 1 Chromosomes
and Inheritance
Effects of Gene Location, continued
• Linked Genes
– Pairs of genes that tend to be inherited
together are called linked genes.
– Why are these genes inherited together?
• They are inherited together because they
are found on the same chromosome.
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Chapter 12
Section 1 Chromosomes
and Inheritance
Effects of Gene Location, continued
• Chromosome Mapping
– The farther apart two genes are located on a
chromosome, the more likely a cross-over will
occur.
• Example: If 2 genes are 2 times further apart
than 2 other genes, what is the chances a
cross-over will occur?
• TWICE AS LIKELY
– Researchers use recombinant percentages to
construct chromosome maps showing relative
gene positions.
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Chapter 12
Section 1 Chromosomes
and Inheritance
Mutations
• Germ-cell mutations occur in gametes and can be
passed on to offspring.
– Example: Colorblindness.
• Somatic-cell mutations occur in body
that affect only the individual organism.
– Example: skin cancer; cause by ??????
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Chapter 12
Section 1 Chromosomes
and Inheritance
Mutations, continued
• Chromosome Mutations
– Chromosome mutations are changes in the
structure of a chromosome or the loss or gain
of an entire chromosome.
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Chapter 12
Section 1 Chromosomes
and Inheritance
Chromosomal Mutations
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Chapter 12
Section 1 Chromosomes
and Inheritance
Mutations, continued
• Gene Mutations
– Gene mutations are changes in one or more of the
nucleotides in a gene.
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Chapter 12
Section 1 Chromosomes
and Inheritance
Gene Mutations
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Chapter 12
Section 2 Human Genetics
Inheritance of Traits
• Pedigrees
– Geneticists use pedigrees to trace diseases or
traits through families.
– Pedigrees are diagrams that reveal inheritance
patterns of genes.
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Chapter 12
Section 2 Human Genetics
Pedigree for Cystic Fibrosis
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Chapter 12
Section 2 Human Genetics
Some Important
Genetic
Disorders
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Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders
• Polygenic Inheritance
– Polygenic characters, such as skin color, are
controlled by two or more genes.
• Melanin: a protein that determines how
much skin color is going to be deposited in
a skin cell. More melanin produced, more
color is deposited.
• Other polygenic characteristics: eye color,
height, and hair color.
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Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders, continued
• Complex Characters
– Many human conditions are complex
characters, such as polygenic traits, are
influenced by both genes and environment.
– How can your skin color be influence by the
environment? Height?
– In diseases: breast cancer, diabetes, heart
disease, stroke, etc.
– Are there ways you can control disease factors
to control your ability to contract a disease?
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Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders, continued
• Multiple Alleles
– Multiple-allele characters, such as ABO blood
groups, are controlled by three or more alleles
of a gene.
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Chapter 12
Section 2 Human Genetics
Comparing Single Allele, Multiple Allele,
and Polygenic Traits
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Chapter 12
Section 2 Human Genetics
Comparing Complete, Incomplete,
and Co-Dominance
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INCOMPLETE
DOMINANCE
• A cross where one allele
does not completely hide or
mask the other producing a
blended appearance in the
phenotype.
• Example: In snapdragons,
pure red crossed with pure
white produce pink!
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CODOMINANCE
• Two non-identical
alleles of a pair
specify two different
phenotypes yet one
cannot mask the
other and both are
expressed .
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Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders, continued
• X-Linked Traits
– The gene for colorblindness, an X-linked recessive
gene, is found on the X chromosome.
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Chapter 12
Section 2 Human Genetics
Genetic Traits and Disorders, continued
• Sex-influenced Trait
– A sex-influenced trait, such as pattern baldness, is
expressed differently in men than in women even
if it is on an autosome and both sexes have the
same genotype.
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Chapter 12
Section 2 Human Genetics
Comparing X-Linked and Sex-Influenced Traits
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Chapter 12
Section 2 Human Genetics
Detecting Genetic Disease
• Genetic screening examines a person’s genetic
makeup and potential risks of passing disorders to
offspring.
• Amniocentesis and chorionic villi sampling help
physicians test a fetus for the presence of genetic
disorders.
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Chapter 12
Section 2 Human Genetics
Detecting Genetic Disease, continued
• Genetic Counseling
– Genetic counseling informs screened individuals
about problems that might affect their offspring.
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Chapter 12
Section 2 Human Genetics
Treating Genetic Disease
• Genetic disorders are treated in various ways.
• Among the treatments are symptom-relieving
treatments and symptom-prevention measures, such
as insulin injections for diabetes.
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Chapter 12
Section 2 Human Genetics
Genetic Disorder
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Chapter 12
Section 2 Human Genetics
Treating Genetic Disease, continued
• Gene Therapy
– In gene therapy, a defective gene is replaced with
a copy of a healthy gene.
– Somatic cell gene therapy alters only body cells.
– Germ cell gene therapy attempts to alter eggs or
sperm.
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Chapter 12
Standardized Test Prep
Multiple Choice
1. Which can a chromosomal map show?
A. the sex of the individual
B. the presence of mutant alleles
C. the positions of genes on a chromosome
D. whether a gene is autosomal or recessive
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
1. Which can a chromosomal map show?
A. the sex of the individual
B. the presence of mutant alleles
C. the positions of genes on a chromosome
D. whether a gene is autosomal or recessive
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
2. Which can result from the deletion of a single
nucleotide?
F. trisomy
G. a translocation
H. nondisjunction
J. a frameshift mutation
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
2. Which can result from the deletion of a single
nucleotide?
F. trisomy
G. a translocation
H. nondisjunction
J. a frameshift mutation
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
3. At the present time amniocentesis cannot reveal
which of the following?
A. eye color
B. genetic disease
C. sex of the fetus
D. chromosomal abnormalities
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
3. At the present time amniocentesis cannot reveal
which of the following?
A. eye color
B. genetic disease
C. sex of the fetus
D. chromosomal abnormalities
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
4. A geneticist working with the fruit fly Drosophila
melanogaster discovers a mutant phenotype that
appears only in males who are offspring of males of
the same phenotype. What does this information
suggest about the mutant phenotype?
F. The trait is X-linked.
G. The trait is Y-linked.
H. The trait is autosomal dominant.
J. The trait is autosomal recessive.
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
4. A geneticist working with the fruit fly Drosophila
melanogaster discovers a mutant phenotype that
appears only in males who are offspring of males of
the same phenotype. What does this information
suggest about the mutant phenotype?
F. The trait is X-linked.
G. The trait is Y-linked.
H. The trait is autosomal dominant.
J. The trait is autosomal recessive.
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
The table below shows
5. Which statement best
the genotypes and phenotypes of
explains why men and
pattern baldness.
women express the Bb
Use the table to answer the
genotype differently?
question that follows.
A. The trait is polygenic.
B. The trait has multiple
alleles.
C. Pattern baldness is a
sex-linked trait.
D. Pattern baldness is a
sex-influenced trait.
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
The table below shows
5. Which statement best
the genotypes and phenotypes of
explains why men and
pattern baldness.
women express the Bb
Use the table to answer the
genotype differently?
question that follows.
A. The trait is polygenic.
B. The trait has multiple
alleles.
C. Pattern baldness is a
sex-linked trait.
D. Pattern baldness is a
sex-influenced trait.
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Standardized Test Prep
Multiple Choice, continued
6. translocation : chromosome mutation :: substitution
F. gene mutation
G. point mutation
H. germ-cell mutation
J. somatic-cell mutation
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
6. translocation : chromosome mutation :: substitution
F. gene mutation
G. point mutation
H. germ-cell mutation
J. somatic-cell mutation
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
The image below is a
7. Which type of inheritance
pedigree showing the
pattern is associated with
inheritance of hemophilia in a
hemophilia?
family. Use the pedigree to
answer the question that
A. autosomal recessive
follows.
B. sex-linked dominant
C. sex-linked recessive
D. autosomal dominant
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Chapter 12
Standardized Test Prep
Multiple Choice, continued
The image below is a
7. Which type of inheritance
pedigree showing the
pattern is associated with
inheritance of hemophilia in a
hemophilia?
family. Use the pedigree to
answer the question that
A. autosomal recessive
follows.
B. sex-linked dominant
C. sex-linked recessive
D. autosomal dominant
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Chapter 12
Standardized Test Prep
Short Response
Consider a couple about to get married. The woman
has cystic fibrosis, but the man does not.
What benefit would they gain by seeing a genetic
counselor?
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Chapter 12
Standardized Test Prep
Short Response, continued
Consider a couple about to get married. The woman
has cystic fibrosis, but the man does not.
What benefit would they gain by seeing a genetic
counselor?
Answer:
Genetic counseling will tell them the likelihood of
each of their children having cystic fibrosis or carrying
the cystic fibrosis gene.
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Chapter 12
Standardized Test Prep
Extended Response
Colorblindness is a recessive, sex-linked trait. A
woman and a man, both with normal vision, have
three daughters with normal vision. One of the
daughters marries a man with normal vision, and
they have a son who is colorblind.
Part A Which parent of the son is the carrier of the
trait? Explain your answer.
Part B What is the likelihood that the children of a
woman heterozygous for colorblindness and
colorblind man will express the trait? Explain
your answer.
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Chapter 12
Standardized Test Prep
Extended Response, continued
Answer:
Part A The son’s mother carries the trait. The gene for
colorblindness is carried on the X chromosome.
Part B Given: X-linked recessive: heterozygous female = XB
(normal)Xb (colorblind); colorblind male = Xb (colorblind)Y.
This Punnett square predicts that 50 percent of the
children will be male and 50 percent of the children will be
female. 50 percent will be colorblind and 50 percent will
have normal vision. 25 percent will be males with normal
vision and will not be carriers. 25 percent will be female
carriers with normal vision. 25 percent will be colorblind
females. 25 percent will be colorblind males.
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