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Name: __________________________________________________________ Hour: __________ Teacher: ROZEMA

Biology

Genetics Unit

[Packet-4] What do we know so far?

Video Observations: DNA:

DMD Basic Information: Proteins:

Muscles: Mutations:

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Which Questions Have We Answered?

What causes the disorder?

What role does DNA play in the disorder?

Did the disorder come from their parents?

How could the parents be normal but not the kids?

Did the disorder come from someone else in the family?

What does the disorder do to the muscles?

Why is the disorder more common in males?

Is the disorder affected by weak / strong traits?

How common is the disorder? Can you predict a chance of having a kid with the disorder?

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Lesson 6 Inheritance of Genes Reading: How did the boys in the video get the mutation that

results in DMD?

The Inheritance of Genes

Part 1: Genes and Alleles What is a gene? Genes are segments of DNA that code for the production of specific proteins. The code of DNA is made up of four

nucleotides that are named for the unique base making them up: adenine (A), thymine (T), guanine (G), and cytosine

(C). These four specific building blocks make up the “letters” of the DNA alphabet. The order of DNA nucleotides is

important for the production of a functional protein. How many genes do humans have? A genome is all of the genetic material in an individual cell of an organism. All cells in that organism contain the same

genome. It is estimated that the human genome contains about 20,000 genes. Out of these 20,000 genes, over 100,000

different proteins can be made! This is because the coding regions in genes can be recombined with different segments to

code for different proteins. There are over 6 billion nucleotides in the human genome, yet only 1.5% of those nucleotides

actually code for proteins. The remaining 98% nucleotides of the genome don’t code for proteins. Some of the sequences

in this portion of the genome work to turn genes “on or off.” That is, they control whether certain proteins are made or

not. What are alleles? Each cell actually contains two copies of each gene. The copies could be identical or they could be different versions of

the same gene called alleles. For example, everyone has a pair of genes that code for blood type. A person with Type AB

blood has one allele that codes for A-type blood cell proteins and another allele that codes for B-type blood cell proteins,

while a person with Type O blood has two alleles that don’t code for the proteins at all, so the proteins are missing.

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Part 2: Chromosomes Adapted from "Chromosomes." National Human Genome Research Institute. National Human Genome Research

Institute, 16 June 2015. Web. 12 Aug. 2016. <https://www.genome.gov/26524120/>. What is a chromosome? Chromosomes are structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein

and a single molecule of deoxyribonucleic acid (DNA), which is condensed and folded around the protein.

What do chromosomes do? The unique structure of chromosomes keeps DNA tightly wrapped around spool-like proteins, called histones. Without

such packaging, DNA molecules would be too long to fit inside cells. For example, if all of the DNA molecules in a single

human cell were unwound from their histones and placed end-to-end, they would stretch 6 feet. For an organism to grow and function properly, cells must constantly divide to produce new cells to replace old, worn-out

cells. During cell division, it is essential that DNA remains intact and evenly distributed among cells. Chromosomes are a

key part of the process that ensures DNA is accurately copied and distributed in the vast majority of cell divisions. Still,

mistakes do occur on rare occasions. Changes in the number or structure of chromosomes in new cells may lead to serious

problems. For example, in humans, one type of leukemia and some other cancers are caused by defective chromosomes

made up of joined pieces of broken chromosomes. It is also important that reproductive cells, such as eggs and sperm,

contain the right number of chromosomes and that those chromosomes have the correct structure. If not, the resulting

offspring may fail to develop properly. For example, people with Down syndrome have three copies of chromosome 21,

instead of the two copies found in other people. Do all living things have the same types of chromosomes? Chromosomes vary in number and shape among living things. Most bacteria have one or two circular chromosomes.

Humans, along with other animals and plants, have linear chromosomes that are arranged in pairs within the nucleus of

the cell. The only human cells that do not contain pairs of chromosomes are reproductive cells, or gametes, which carry

just one copy of each chromosome. When two reproductive cells unite (fertilization) they become a single cell that

contains two copies of each chromosome (zygote). This cell then divides and its successors divide numerous times,

eventually producing a mature individual with a full set of paired chromosomes in virtually all of its cells. How many chromosomes do humans have? Humans have 23 pairs of chromosomes, for a total of 46 chromosomes. In fact, each species of plants and animals has a

set number of chromosomes. A fruit fly, for example, has four pairs of chromosomes, while a rice plant has 12 pairs and a

dog, 39 pairs. How are chromosomes inherited? In humans and most other complex organisms, one copy of each chromosome is inherited from the female parent and the

other from the male parent. This explains why children inherit some of their traits from their mother and others from their

father. Do males have different chromosomes than females? Yes, they differ in a pair of chromosomes known as the sex chromosomes. Females have two X chromosomes in their

cells, while males have one X and one Y chromosome. Inheriting too many or not enough copies of sex chromosomes can

lead to serious problems. For example, females who have extra copies of the X chromosome are usually taller than

average and some have mental retardation. Males with more than one X chromosome have Klinefelter syndrome, which is

a condition characterized by tall stature and, often, impaired fertility. Another syndrome caused by imbalance in the

number of sex chromosomes is Turner syndrome. Women with Turner have one X chromosome only. They are very short,

usually do not undergo puberty and some may have kidney or heart problems.

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Part 3: Meiosis What is meiosis? Meiosis is a process that happens in certain cells that will divide to produce sex cells, also known as gametes. The cells

that will go through meiosis are located in the ovaries for women and in the testes for men. Recall that there are 23 pairs

of chromosomes in all human body cells, also known as somatic cells, making a total of 46 chromosomes in each

cell. The goal of meiosis is to separate each pair of chromosomes into two new cells, each cell having one of

chromosome instead of two. How does meiosis begin? The first thing that takes place prior to meiosis of the special ovary or testes cells is DNA replication. Each DNA

molecule making up a chromosome is split between the base pairs, forming two parent DNA strands. Free nucleotides

with complementary bases are matched to each parent strand. By the end of DNA replication, every chromosome has

made its own copy which is then attached to itself. Anytime DNA is replicated, there is a chance that mutations can

occur. The wrong base could substitute for the correct base, or a base could be deleted or inserted. After replication, the

DNA molecule gets packaged very tightly into a condensed chromosome with an X-like shape. How are the chromosome pairs separated in order to create two new cells?

An amazing thing happens once the DNA is packaged into chromosomes--each chromosome matches up with its partner

chromosome carrying the same genes. Each pair of chromosomes then embraces, and segments of one chromosome

switch places with the similar segments of its partner. This exchange of genetic material is called crossing

over. Crossing over creates chromosomes with a different combination of alleles than originally inherited from one’s

parents. After crossing over, the paired chromosomes (homologous chromosomes) all line up in the middle of the

cell. The random lining-up of homologous pairs at the cell’s middle is called independent assortment. From there, each

chromosome of the pair is pulled by special fibers to the opposite sides of the cell. The cell then divides into two. At this

point, the two cells that have been created, called daughter cells, each contain just one of each chromosome--one set

instead of two, however each chromosome is still duplicated because DNA replication happened at the beginning. The

next part of meiosis is to separate the chromosome copies. In each daughter cell, the X-shaped chromosomes line up at

the middle of the cell. The two sides of the X’s are then pulled by fibers to the opposite sides of the cell. Each daughter

cell divides once more so that the end result of meiosis is four daughter cells, each with one set of single

chromosomes. We call the daughter cells with just one set of (23) chromosomes gametes.

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What happens to the gametes after meiosis? Sperm and egg are both gametes with one set of chromosomes each. When the two join, their chromosome sets combine,

and the chromosome number is now the same as the original cell that started meiosis in the first place! The new cell that

is formed is called a zygote. It will divide again and again until it becomes a new offspring. When the zygote divides, does it do meiosis or something different? Almost all of the cells that descend from the zygote are called somatic cells, from the Greek word “soma” meaning

body. Somatic cells are cells that make up all of the body except for the gametes. Gametes are known as germline cells.

Germline cells transfer genetic information from one generation to the next. Both somatic cells and germline cells

replicate their DNA prior to cell division. As you read earlier, the cells that create gametes go through meiosis, a special

type of cell division that reduces the chromosome number in half. We wouldn’t want that to happen to all body cells, so

somatic cells go through a cell division process called mitosis. How does mitosis work? Mitosis is like meiosis but simpler. The homologous chromosomes don’t pair up, there is no crossing over, and there

aren’t two rounds of cell division. In mitosis, each chromosome replicates and then condenses into the compact X-shaped

form. The chromosomes line up in the middle of the cell. Each copy of the chromosome is then separated from the other

and pulled to opposite sides of the cell. After this, the parent cell splits in the middle to form two daughter cells each with

the same number of chromosomes as the parent cell had at the start of mitosis.

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OBTAINING AND COMMUNICATING INFORMATION: As you read the informational text about the inheritance of genes, answer the following questions. 1. What is a gene?

2. What is an allele?

3. What is a chromosome?

4. Why is it important for DNA to condense into chromosomes?

5. Can a person have more than 46 chromosomes? What would be the result if this happened?

6. How many chromosomes do humans have?

7. Are there differences between the chromosomes of males and females?

8. What is a gamete?

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9. What is crossing over?

10. What are homologous chromosomes?

11. What is independent assortment?

12. What is meiosis?

13. Why is meiosis important?

14. What is a zygote?

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15. What are somatic cells?

16. What are germline cells?

17. How is mitosis different from meiosis?

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18. Vocabulary Practice- After you read the informational text about the inheritance of genes, match the following

definitions to their vocabulary term. Word Bank

Genome Allele Chromosomes sex chromosomes Meiosis Gametes somatic cells crossing over homologous chromosomes zygote germline cells independent assortment Mitosis

Vocabulary Term Definition

The chromosomes that determine your biological sex - X and Y

The set of alleles an organism inherits

Versions of a gene that arise through mutation

Cell division that occurs in sex cells

Egg and sperm cells

The complete set of genes in an organism

Cell division that occurs in all body cells

The matching chromosomes a person inherits from their mother and father

A process that increases genetic diversity during meiosis

Cells that divide to produce gametes

The cell formed when an egg and sperm meet

Body cells (hair, skin, brain, bone, etc)

The random lining-up of homologous pairs at the cell’s middle

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-Diagram Summary of Lesson 6 Content-

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Lesson 7 Student Activity Sheet: Why is DMD affecting mostly boys?

PRIOR KNOWLEDGE: 1. What do you already know about the difference between dominant and recessive traits? Or sex-linked and autosomal

traits?

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Case Study 1: Cystic Fibrosis (adapted from: https://www.cff.org/What-is-CF/About-Cystic-Fibrosis/ Images from:

http://archive.industry.gov.au/Biotechnologyonline.gov.au/popups/img_cffamilytree.html)

Cystic fibrosis is a progressive, genetic disease that causes persistent lung infections and limits the ability to breathe over

time. In people with CF, a defective gene causes a thick, sticky buildup of mucus in the lungs, pancreas, and other organs.

In the lungs, the mucus clogs the airways and traps bacteria leading to infections, extensive lung damage, and eventually,

respiratory failure. In the pancreas, the mucus prevents the release of digestive enzymes that allow the body to break down

food and absorb vital nutrients. Cystic fibrosis is a genetic disease. People with CF have inherited two copies of the

defective CF gene -- one copy from each parent. Both parents must have at least one copy of the defective gene, making

the gene for CF autosomal recessive. People with only one copy of the defective CF gene are called carriers, but they do

not have the disease. Carriers are not affected by cystic fibrosis because the normal gene compensates for the faulty one.

The diagram below is called a pedigree and it illustrates how genes for diseases like Cystic Fibrosis can be passed from

parents to their children.

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2. Using the letters A and a, what is the genotype for each of the following people?

Person 1: _______

The father of person 2: _______

Both parents of person 3: ________

3. Is Cystic Fibrosis dominant or recessive? Use evidence from the reading and pedigree to support your answer.

4. Person 4 has a child with someone who is a carrier of CF. Complete a Punnett Square to determine the chance their

offspring will have Cystic Fibrosis.

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Case Study 2: Huntington’s Disease (adapted from: http://hdsa.org/what-is-hd/ Image from: http://torresbioclan.pbworks.com/w/page/22377142/Huntingtons-Disease)

Huntington's Disease, or Huntington's Chorea, is a rare autosomal dominant disease that results in the slow deterioration

of the physical and mental abilities of the affected person. Experts estimate that one in every 10,000 people (about 30,000

Americans) suffer from Huntington disease and another 150,000 are at risk for developing it. Many describe the

symptoms of HD as having ALS, Parkinson’s and Alzheimer’s – simultaneously.

Symptoms usually appear between the ages of 30 to 50, and worsen over a 10 to 25 year period. Ultimately, the weakened

individual succumbs to pneumonia, heart failure or other complications. Every person who inherits the HD gene will

eventually develop the disease. Over time, HD affects the individual’s ability to reason, walk and speak. Since the disease

does not manifest until a late age, an affected person will often have children already. You can take genetic tests to see if

you are at risk for the disease.

Use this pedigree to answer the questions about Huntington’s.

5. Using the letters H and h, what is the genotype for each of the following people?

Person 1: _______

Person 2: _______

Person 3: ________

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6. Is Huntington’s dominant or recessive? Use evidence from the reading and pedigree to support your answer.

7. Person 3 has a child with someone who does not have Huntington’s. Complete a Punnett Square to determine the

chance their offspring will have Huntington’s.

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Case Study 3: Hemophilia (adapted from: https://www.hemophilia.org/Bleeding-Disorders/Types-of-Bleeding-Disorders/Hemophilia-A image from:

https://www.genomicseducation.hee.nhs.uk/modes-of-inheritance/x-linked-conditions/)

Hemophilia A, is a genetic disorder caused by a missing blood clotting protein. People with hemophilia A often, bleed

longer than other people. Bleeds can occur internally, into joints and muscles, or externally, from minor cuts, dental

procedures or trauma. According to the US Centers for Disease Control and Prevention, hemophilia occurs in

approximately 1 in 5,000 live births. There are about 20,000 people with hemophilia in the US. All races and ethnic

groups are affected.

The X and Y chromosomes are called sex chromosomes. The gene for hemophilia is carried on the X chromosome.

Hemophilia is inherited in an X-linked recessive manner. Females inherit two X chromosomes, one from their mother and

one from their father (XX). Males inherit an X chromosome from their mother and a Y chromosome from their father

(XY). That means if a son inherits an X chromosome carrying hemophilia from his mother, he will have hemophilia. It

also means that fathers cannot pass hemophilia on to their sons.

But because daughters have two X chromosomes, even if they inherit the hemophilia gene from their mother, most likely

they will inherit a healthy X chromosome from their father and not have hemophilia. A daughter who inherits an X

chromosome that contains the gene for hemophilia is called a carrier. She can pass the gene on to her children.

Hemophilia can occur in daughters, but is rare.

8. Sex linked traits are typically carried on the X chromosome. To denote the genotypes, a superscript is used. A female

carrier of hemophilia will have the genotype XHXh .Using the letters X and Y, what is the genotype for each of the

following people?

Person 1: _______

Person 2: _______

Person 3: ________

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9. If you have the gene for hemophilia, will you always have hemophilia? Under what circumstances could you not have

hemophilia? Use evidence from the reading and pedigree to support your answer.

10. Person 3 has a second child, a daughter. Complete a Punnett Square to determine the chance this child will have

hemophilia.

CONCLUSION: 11. Why does DMD affect mostly boys? What type of inheritance pattern does DMD follow? Use evidence from the

video and the case studies in your answer.

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Lesson 8 Student Activity Sheet: What is our model to explain what is happening in people

with DMD?

Use the space provided to answer the questions and draw a model to explain how the boys in the video (and anyone with

DMD) acquired it and how this relates to their physical symptoms. 1. How does someone acquire (get) Duchenne Muscular Dystrophy? Is DMD inherited from a person’s parents or do

they get it from the environment? Explain & Draw a Labeled Diagram (to help support your explanation)

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2. Who is more likely to acquire DMD, boys or girls? Why is that? Could a person have a mutated gene for

dystrophin but not have DMD? How? Explain & Draw a Labeled Diagram (to help support your explanation)

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3. It’s very rare for someone with two X chromosomes to have DMD. Explain how a person with two X

chromosomes could have the symptoms of DMD using what you know about inheritance and random mutation.

Explain & Draw a Labeled Diagram (to help support your explanation)

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4. People who have muscular dystrophy have something called a “mutation.” How does that mutation arise? Be

sure to show what is happening to DNA and mRNA. Explain & Draw a Labeled Diagram (to help support your

explanation)

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5. Genes include information used to make something in cells. What is supposed to happen with the information on

the gene for dystrophin and what happens when a person has a mutation of the gene? Explain & Draw a Labeled

Diagram (to help support your explanation)

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6. What is the function of dystrophin in muscles? How does a mutation affect the function of dystrophin? Be sure

to explain how different types of mutations cause different types of muscular dystrophy. Explain & Draw a Labeled

Diagram (to help support your explanation)

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7. If we found a way to repair a single cell with the DMD gene in a 2-year old child, could we cure DMD by

repairing that single cell? Explain & Draw a Labeled Diagram (to help support your explanation)

8. Over time, what happens to the muscles of people with DMD? Why is there controversy about whether DMD

patients should engage in normal exercise, such as running? Why do some doctors recommend it, even though

others think it is risky? Explain & Draw a Labeled Diagram (to help support your explanation)