View
116
Download
0
Category
Preview:
DESCRIPTION
Citation preview
Chapter
14
Human Heredity
14-1 Human Heredity
Scientists once knew much less about humans then about other “model” organisms such as fruit flies and mice
With the completion of the Human Genome Project scientists are on verge of understanding human genetics at least as well as they understand that of some other organisms
Human Chromosomes
To analyze chromosomes, cell biologists photograph cells in mitosis Chromosomes are fully condensed and easiest to see during ____________________
Karyotype - ____________________________________________________________________________________________________________________________________
2
We all began life when a haploid sperm fertilized a haploid egg carrying just ________ chromosomes each.
The _________________________ zygote or fertilized egg contained the full complement of __________ chromosomes
Sex chromosomes - ______________________________________________________________________________________________________________________________
Females: ___________
Males: _____________
The regular 44 chromosomes are known as __________________________________
Q: Why are males + females born in a roughly 50:50 ratio?A: All egg cells carry a single _______ chromosome. However, half of all sperm carry an _______ chromosome, the other half carry a ________ chromosome
Human Traits
In order to apply Mendelian genetics to humans, biologists must identify an inherited trait controlled by a single gene
Then, they have to study how the trait is passed from one generation to the next
Pedigree - _______________________________________________________________________________________________________________________________________
3
Most human traits are not coded for by single genes Also, many traits are strongly influenced by environmental factors
o Ex.) average height has increased 10cm in the United States and Europe since 1800’s
Polygenic traits - _________________________________________________________
Human Genes
The human genome - ______________________________________________________ Includes tens of thousands of genes Until recently the identification of a human gene took years of work
Humans aren’t easy test subjectsooo
Blood Group Genes
4
A number of genes are responsible for human blood groups, but the best known are the ABO and Rh blood groups
Rh blood group Single gene with two alleles
Rh + (dominant)Rh - (recessive)
Recessive alleles
Many human genes have become known through the study of genetic disorders
Q: How do scientists identify recessive alleles that cause these disorders?A:
PKU – phenylketonuria Lack enzyme needed to break down phenylalanine Found in milk and other foods If newborn has PKU, phenylalanine may build up in the tissues during severe mental
retardation If newborns are tested early, they can be placed on a low phenylalanine diet which
prevents most of the affects PKU is caused by a recessive allele carried on chromosome 12
Tay Sachs Autosomal recessive Found mostly in Jewish families of central and eastern European ancestry Results in nervous system breakdown and death in the first few years of life There is no treatment, but there is a test prospective parents can take
Dominant Alleles
Not all genetic disorders are caused by recessive alleles
Achondropasia – dwarfism Never reach 4 feet 4 inches Cartilage forms in such a way that the arms and legs end up being disproportionately
short 1 in every 10,000 is affected
Huntingtons Progressive loss of muscle control and mental function until death occurs People with disease show no symptoms until they are in their 30’s and 40’s
5
Rh is an antigen found in the blood of about 85% of all people; these people are said to be Rh positive. The rest of the population is Rh negative
Codominant Alleles
Sickle cell disease Affects 1 in 500 African Americans
From Gene to Molecule
Cystic Fibrosis (CF) Most common among people whose ancestors come from northern europe Caused by a recessive allele on chromosome 7 Produce a thick heavy mucus that clogs their lungs and breathing passageways Serious digestive problems Only half survive into their 20’s
Sickle Cell Disease
Characterized by the bent and twisted shape of the red blood cell Sickle shaped red blood cell tend to get stuck in the capillaries Produce physical weakness and damage to the brain, heart and spleen Sometimes fatal Change in _______________________ DNA base This change inserts amino acid ______________________ in place of
__________________________________
6
Hemoglobin molecules stick together and form long chains that produce the characteristic shape of sickled cells
Q: Why do so many African Americans carry the sickle cell alleleA: Many African Americans have ____________________________________________ancestry where _________________________ is a serious problem
People who are heterozygous for the sickle cell allele don’t get sickle cell and they don’t get malaria
Dominant or Recessive
It all depends on the nature of a genes protein product and its role in the cell
Ex.) In CF, one copy of the normal allele can supply cells with enough chloride channel proteins to function therefore the normal CF allele is considered ____________________
7
Malaria and the Sickle Cell Allele
The map on the left shows where malaria is common. The map on the right shows regions where people have the sickle cell allele.
Name ____________________________________ Date __________________ Per ____
14-1 Section Review
8
1. What are sex chromosomes? What determines whether a person is male or female?
2. Using an example, explain how a small change in a person’s DNA can cause a genetic disorder.
3. How does studying genetic disorders such as PKU help biologists understand normal alleles?
4. What are some problems biologists face in studying human inheritance?
5. Critical Thinking Predicting If a woman with type O blood and a man with type AB blood have children, what are the children’s possible genotypes?
14-2 Human Chromosomes
A human diploid cell contains more than ____________________________ nucleiotide pairs of DNA
Despite its size, all of this information is neatly packed into the 46 chromosomes present in every diploid cell
9
Each chromosome is like a library containing hundreds or even thousands of books Biologists are many decades away from mastering the contents of these books, but
they are learning just how many books there are and what they deal with
Sex Linked Genes Genes located on the sex chromosomes Most found on the ________ chromosome
Colorblindness Gene associated with color vision are located on the X
chromosome Affects 1 in 10 males Affects 1 in 100 females
Q: Why the difference between the sexes?A: Males have ____________________________ X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive In order for a woman to be affected, there must be
__________________________ of the allele
Ex.) What is the probability of a normal vision male and a female who is a carrier for the color blind trait having a child that is color blind?
Hemophilia A protein necessary for normal
________________________________ is missing 1 in 10,000 males
10
People with hemophilia can bleed to death from minor cuts and may suffer from internal bleeding
Treated with normal clotting factors
Duchenne Muscular Dystrophy Results in progressive weaking and loss of skeletal muscle Rarely live past early adulthood In the U.S. 1 in 3000 males is born with Duchenne muscular dystrophy Caused by a defective version of the gene that codes for a muscle protein
X-Chromosome Inactivation
Q: If all you need is one X chromosome, what happens to the extra X chromosome in females?
A:
Same in cats, that’s why you can have cats with 3 different colorso Fur color is on the X chromosome. Some areas have one color switched on,
and others its switched off
Calico Cat: This cat’s fur color is controlled by a gene on the X chromosome.
Chromosomal Disorders
Nondisjunction - __________________________________________________________
11
________________________________________________________________________
If nondisjunction occurs, ________________________________________________________________________________________________________________________________________________________________________________________________
Disorders of Chromosome Numbers
Down Syndrome When nondisjunction happens and a baby is born with _________________________
of __________________________________________ Trisomy 21 1 in 800 in U.S. Mild to severe retardation Susceptible to many diseases Increased frequency of birth defects
Sex Chromosome Disorders
Turners Syndrome (female)
12
Only inherit one ___________________________________ Genotype = ___________ Women with Turner syndrome are sterile, their sex organs don’t properly develop at
puberty
Klinefelters Syndrome (males) Inherit ___________________________________________ Genotype = ________________ The extra X interferes with meiosis and usually prevents them from reproducing Some cases _______________________________________
These abnormalities show us the role of Y in sex determinationo Even in combination with several X’s, the Y makes them male
But if this Y is absent, the embryo develops into a female
13
Name __________________________________ Date __________________ Per ______
14-2 Section Review
1. Why are sex-linked disorders more common in males than in females?
2. How does nondisjunction cause chromosome number disorders?
3. List at least two examples of human sex-linked disorders.
4. Describe two sex chromosome disorders.
5. Critical Thinking Comparing and Contrasting Distinguish between sex-linked disorders and sex chromosome disorders.
Extra Credit
Animating Nondisjunction Make a flip book to animate nondisjunction during meiosis. First, make a series of 6 to 10 drawings that gradually show the process of nondisjunction. Then, put the process in motion by flipping the pages with your thumb.
14-3 Human Molecular Genetics
14
Human DNA Analysis
Way too much DNA to search through Biologists search the volumes of the human genome using DNA sequences
Testing for Alleles
If two prospective parents suspect they might be carrying recessive alleles for a genetic disorder they can now get a test to determine the risk of passing that trait on to their children
o Use labeled DNA probes to detect specific sequences found in disease causing alleles
o Looking at changes in restrictive enzyme cutting siteso Looking at differences in lengths of alleles
DNA Fingerprinting
Because the human genome is so complex, no individual is exactly like any other
DNA fingerprinting - ______________________________________________________________________________________________________________________________________________________________________________________________________ Used to settle paternity disputes Convict criminals and overturn convictions
The Human Genome Project
Advances in DNA sequencing technologies at the close of the twentieth century made it possible to begin sequencing entire genomes
At first, biologists worked on small genomes of viruses and bacteria
In 1990, scientists in the United States and other countries began the Human Genome Project
o An attempt to sequence all human DNA In 2000 scientists announced that the DNA sequence of the human genome was
essentially complete We estimate as little as 31,000 genes
o Fruit fly – 14,000o C. elegans worm 20,000
Now the task is to figure out how so few genes make an organism as complex as us
Searching for genes
15
Promoter – ______________________________________________________ Researchers are looking for genes that provide useful clues to some of the basic
properties of life Also looking for genetic information that may be useful in developing new drugs and
treatment of disease
A Breakthrough for Everyone Data from the human genome project is posted on the internet on a daily basis www.genome.gov
Gene Therapy The most obvious use of info about the human genome would be to cure genetic
disorders by gene therapy
Gene therapy - ___________________________________________________________________________________________________________________________________
Ethical Issues in Human Genetics
16
Not always been successful, no lasting cure yet
There are many questions which science will rapidly force society to come to grips with
If it’s just as easy to manipulate genes for personal preference then it is to cure a disease should we do it?
Our society will have to develop a thoughtful and ethical conscious of what should and shouldn’t be done with the human genome
Name ____________________________________ Date _________________ Per _____
17
14-3 Section Review
1. What is the Human Genome Project?
2. Describe how gene therapy works.
3. Name two common uses for DNA testing.
4. Describe how molecular biologists identify genes in sequences of DNA.
5. Critical Thinking Making Judgments Do you think it should be legal for people to use genetic engineering to affect their children’s characteristics? Give reasons for your answer.
Chapter 14 The Human Genome
18
Reviewing ContentChoose the best answer. 1. A normal human diploid zygote contains a full set of
23 chromosomes.
46 chromosomes.
44 chromosomes.
XXY chromosomes.
2. A chart that traces the inheritance of a trait in a family is called a(an)
pedigree.
karyotype.
genome.
autosome.
3. Traits that are caused by the interaction of many genes are said to be
polyploid.
linked.
polygenic.
autosomal.
4. An example of a trait that is determined by multiple alleles is
Huntington’s disease.
ABO blood groups.
Down syndrome.
hemophilia.
5. Most sex-linked genes are found on the
Y chromosome.
O chromosome.
YY chromosomes.
X chromosome.
6. Hemophilia is a genetic disorder that is
sex-linked.
sex-influenced.
fairly common.
19
more common in women than men.
7. Which parental pair could produce females with colorblindness?
homozygous normal-vision mother, father with colorblindness
mother with colorblindness, normal-vision father
heterozygous normal-vision mother, normal-vision father
heterozygous normal-vision mother, father with colorblindness
8. A common genetic disorder characterized by bent and twisted red blood cells is
cystic fibrosis.
hemophilia.
sickle cell disease.
muscular dystrophy.
9. Which of the following techniques takes advantage of repeated DNA sequences that do not code for proteins?
DNA fingerprinting
DNA sequencing
genetic engineering
rapid sequencing
10. The process of attempting to cure genetic disorders by placing copies of healthy genes into cells that lack them is known as
gene therapy.
DNA fingerprinting.
rapid sequencing.
the Human Genome Project.
20
Recommended