key concept the chromosomes on which genes are located …€¦ · a man and a woman marry. the...

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KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

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Page 1: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

KEY CONCEPT

The chromosomes on which genes are located gcan affect the expression of traits.

Page 2: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Two copies of each autosomal gene affect p gphenotype.

• Mendel studied autosomal• Mendel studied autosomalgene traits (these genes are on autosomes), like hair texture.

• The “either‐or” traits that were seen in your tutorialwere seen in your tutorial.

Page 3: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

• Mendel’s rules of inheritance apply to autosomalti di dgenetic disorders.

– A heterozygous for a recessive disorder is a carrier. – Disorders caused by dominant alleles are uncommon, but y ,

possible.

(dominant)(dominant)

Page 4: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

• What about genes located on sex• What about genes located on sex chromosomes? What are these traits called?

Page 5: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Males and females can differ in sex‐l k dlinked traits.    

• Genes on sex chromosomes are called sex‐linked genes. Y h i l ibl f l– Y chromosome genes in mammals are responsible for male characteristics.

– X chromosome genes in mammals affect many traits.

Page 6: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

• Male mammals have an XY genotype.– All of a male’s sex-

linked genes are expressedexpressed.

– Males have no second copies of sex-linked genes.

– Because of this, males can never bemales can never be “carriers” of sex-linked traits or disorders.

– Ex: Colorblindness, Hemophilia MuscularHemophilia, Muscular dystrophy

Page 7: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Sample Colorblind Tests

4 Sex‐Linked Traits:

1 N l C l Vi i

Tests

1. Normal Color Vision:A: 29, B: 45, C: ‐‐, D: 26

2 R d G C l Bli d2. Red‐Green Color‐Blind:A: 70, B: ‐‐, C: 5, D: ‐‐

3. Red Color‐blind:A: 70, B: ‐‐, C: 5, D: 6

4. Green Color‐Blind:A: 70, B: ‐‐, C: 5, D: 2

Page 8: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Let’s take a look at…Let s take a look at…

Page 9: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Lynda is a healthy carrier of colorblindess and her husband, Jim, has no family historyand her husband, Jim, has no family history 

of colorblindness. Lynda’s genotype:

What is the probability ofXXdJim’s genotype:

XY

What is the probability of

getting:

• A colorblind daughter?

0%

• Carrier child?

25%

• A colorblind child?

25%

T h lth hild ?• Two healthy children?

¾   x  ¾  =  9/16  (56%)

Page 10: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Jen is a healthy carrier of hemophilia and Adam has no history in his family.y y

What is the probability of

getting:getting:

• Daughter with hemophilia?• Daughter with hemophilia?

0%

• Carrier child?• Carrier child?

25%

Child i h h hili ?• Child with hemophilia?

25%

• Two healthy children?

¾   x  ¾  =  9/16  (56%)

Page 11: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Kelly is a healthy carrier of hemophilia, but Joe suffers from the disease.suffers from the disease.

What is the probability of ttigetting a:

• Healthy son?

25%

• Healthy daughter?

25%

• Child with hemophilia?Child with hemophilia?

50%

• Carrier child?• Carrier child?

25%

Page 12: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

We use PEDIGREES to trace:

• Autosomal traitsAutosomal traits

• Sex‐linked traits

• Autosomal disorders orAutosomal disorders or diseases

• Sex‐linked disorders orSex linked disorders or diseases

Page 13: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

A pedigree is a chart for tracing genes in f ila family.    

• Phenotypes are used to infer genotypes on a pedigree.• Autosomal genes show different patterns on a pedigree• Autosomal genes show different patterns on a pedigree than sex‐linked genes. 

Page 14: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

• If the phenotype is more common in males, the gene is likely sex-linked.

Page 15: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Creating a Pedigree

H Hh hKey

H = Healthy

hh H H? ?

H = Healthy

h = PKU

• 1) Manny and Rosa are married and both are healthy.• 2) They have 3 children• 2) They have 3 children.• 3) Their oldest child, Jacob, has a recessive disorder called PKU.

• 4) Their middle child Erica and their youngest Matthew are healthy.

• If healthy is dominant to PKU, fill in the missing genotypes. (start with what you know)

Page 16: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

The Next Generation

Key

HhH hH = Healthy

h = PKU

• 5) Erica meets Moe at college and the two become

hhH?

• 5) Erica meets Moe at college and the two become married.

• 6) Erica and Moe have 2 daughters.6) Erica and Moe have 2 daughters.• 7) Their youngest daughter Jamie shows signs of PKU while Amy does not.

• Fill in the genotypes of the four individuals. (start with what you know)

Page 17: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Fill in the X‐linked Pedigree

Page 18: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Sickle cell anemia (recessive) pedigree

hhHhHint: 3 unknown

hh hh Hh HhHhH?

hh

HhHh H?

H?

Key

H = Healthyy

h = Sickle cell anemia

Page 19: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Let’s try a problem:Aman and a woman marryA man and a woman marry. 

The woman is a carrier of colorblindness, an X‐linked disorder. 

They have 4 children, 3 boys and one girl.  ?Two of the boys are colorblind, and the girl is a carrier.

Th i d ht i h lthThe carrier daughter marries a healthy man. 

a)What is the probability they will ) p y yhave carrier daughters? 

b)What is the probability they will have sons that are colorblind? a) 25%have sons that are colorblind? a) 25%

b) 25%

Page 20: KEY CONCEPT The chromosomes on which genes are located …€¦ · A man and a woman marry. The woman is a carrier of colorblindness, an X‐linked disorder. They have 4 children,

Try this on your own…A man and a woman marry. The man has DMD (a muscular dystrophy disease), which is an X‐linked disease. They have 4 children, 2 carrier daughters and 2 completely healthy boys. One of the carrier daughters marries a healthy man and has 3 children. They have two boys with DMD, and a healthy, non carrier daughter. What is the probability that one of the boys will have sons with disorders if he marries a healthy, non carrier woman?

Now this…Jack and Jill get married. As Jill falls down the hill, she cuts herself and bleeds profusely. She goes to the doctors and realizes that she has hemophilia, an X‐linked blood disorder. They have 5 children, 3 boys and 2 girls, all of which get tested for hemophilia. They discover that 2 boys have hemophilia and one of the daughters is a carrier. One of the affected sons marries a healthy non carrier woman and has twin carrier children. What is the sex of these carriercarrier woman and has twin carrier children. What is the sex of these carrier children? Explain your answer.