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 - ____________________________________________________________________________________________________________________________________

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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 - _______________________________________________________________________________________________________________________________________

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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

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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

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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

__________________________________

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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 ____________________

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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

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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

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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

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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 - __________________________________________________________

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________________________________________________________________________

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)

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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

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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

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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

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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

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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 _____

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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

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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.

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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.

 

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