11.3 Study Guide

Question 1

What is an autosomal trait?

Answer 1

A characteristic determined by a gene located on one of the 22 numbered chromosomes (autosomes), rather than on the sex chromosomes (X and Y)

Question 2

What is a sex-linked trait?

Answer 2

A characteristic determined by genes located on the sex chromosomes (X and Y in humans).

Question 3

If a trait is on an X-Chromosome, how many alleles to biological men and biological women have?

Answer 3

Men - 1
Women - 2

Question 4

Individuals have how many of every autosomal allele?

Answer 4

Two

Question 5

Whether a trait is dominant or recessive often depends on how the mutation in an allele affects this?

Answer 5

Protein(s)

Question 6

Recessive alleles often code for these two kinds of proteins?

Answer 6

1. Malfunctioning Protein
2. No Protein At All

Both result in a loss of function

Question 7

Why are Heterozygotes called “carriers”?

Answer 7

The contain both the dominant and recessive allele but are phenotypically dominant because enough of the properly functioning protein is made.

Question 8

Define and give some examples of human genetic diseases that follow “Dominant autosomal inheritance”.

Answer 8

The mutated allele will code for a protein that does something it is not supposed to and will dominate the normal gene.

Only one affected allele will be enough to develop the disease.

Example: Marfan syndrome

Question 9

Define and give some examples of human genetic diseases that follow “Recessive autosomal inheritance”.

Answer 9

A trait or disorder requires two copies of a mutated allele, one from each parent, to be expressed.

These alleles are located on non-sex chromosomes (autosomes) numbered 1 through 22.

If a person has only one mutated allele, they are a carrier and don’t typically show symptoms but can pass the gene on to their children.

Example: Cystic Fibrosis

Question 10

Define and give some examples of human genetic diseases that follow “X-linked recessive inheritance”

Answer 10

A mutated allele on the X chromosome causes a disorder

Males are more likely to be affected because they only have one X chromosome.

Females, having two X chromosomes, are often carriers and can transmit the gene to their offspring.

Examples include hemophilia A, Duchenne muscular dystrophy, and red-green color blindness.

Question 11

What is Semi-dominant Inheritance?

Answer 11

An inheritance pattern somewhere between dominant and recessive.

Two non-functional copies of the gene causes the full disorder.

One non-functional copy of the gene causes a less severe form of the disorder.

Question 12

Can some genetic disorders have more the one inheritance pattern?

Answer 12

Yes, the type of inheritance pattern depends on the differences and the gene and protein product but can result in the same disorder.

Question 13

What genes are on the Y-Chromosome?

Answer 13

Mainly SRY genes which are sex determining and turn on the production of male hormones.

Question 14

What genes are on the X-Chromosome?

Answer 14

Sex determining genes and MANY other genes and traits.

Results in more disorders being linked to the X-Chromosome

Question 15

What are three X-Chromosome linked disorders?

Answer 15

Hemophilia A
Duchenne muscular dystrophy
Red-green color blindness.

Question 16

Who discovered that sex linked traits were on sex chromosomes as opposed to autosomal chromosomes?

In what years?

At what University?

What did species he use to study sex linked traits? What made this species good studying sex linked traits?

Answer 16

T.H. Morgan

1910-1933

Columbia University

Drosophilia (Fruit Flies)
-prolific
-two week generation
-4 pairs of chromosomes
-XX Female and XY male

Question 17

If a trait is sex-linked recessive (X*)…

1) A female who has the trait would have what genotype?

2) Who did she inherit the disease allele(s) from?

3) A male who has the trait would have what genotype?

4) Who did he inherit the disease allele(s) from?

Answer 17

1) XX

2) Both Mom and Dad

3)X*Y

4) Mom

Question 18

Describe X-Inactivation

Answer 18

A process where one of the two X chromosomes is randomly and permanently inactivated (becomes a Barr body) in each cell.

Happens because female mammals inactivate 2x chromosomes

Question 19

Pedigree Chart Symbols

Answer 19

Reminder to Study Diagram with Symbols and examples on slides 40 - 48

Question 20

Male Pattern Baldness is a “Sex Influenced Trait”. What does that mean?

Answer 20

Comes from an Autosomal Trait but affected by sex hormones

Additionally at least one gene for MPB is X-linked

Age has an affect as well

Question 21

Retinitis Pigmentosa is a progressive disease that results in vision loss. What chromosome is the cause of this disease linked to?

Answer 21

Y Chromosome

Question 22

Does Hemophilia skip generations?

Answer 22

It can because it is a recessive trait.

Question 23

Who do males inherit hemophilia from?

Answer 23

Mom

Question 24

In order for a female to have hemophilia, who would she have to inherit it from?

Answer 24

Mom and Dad

Question 25

Does Hemophilia affect a higher ratio of males or females?

Answer 25

Males (X-linked Recessive Trait)

Question 26

Cystic Fibrosis is Autosomal Recessive. 1. Does the trait skip generations? 2. Should it affect a high ratio of males or females?

Answer 26

1. Yes, unaffected parents can have an affected child. (Heterozygous) 2. Equal between males and females since it is an autosomal trait

Question 27

Marfan Syndrome is Autosomal Dominant. 1. What is the likelihood of an offspring having the disease? 2. What is the likelihood of an offspring being a carrier? 3. Can the trait skip generations? 4. Should the trait affect a higher ratio of males to females?

Answer 27

1. 2/4 2. 0 - can't be a carrier if the trait is dominant 3. No 4. No, autosomal means equal opportunity

Question 28

Genetic Disorders are complicated, aside from allele (gene) mutations what other factors can affect symptoms (3 answers) and treatment (1 answer)?

Answer 28

1. Other genes/ traits an individual has affect symptoms 2. Environmental Factors affect symptoms 3. Different Alleles with different resulting proteins affect symptoms 4. Different alleles with different resulting proteins will respond to treatment differently

Question 29

Individuals who share a recent common ancestor are more likely to have what? This is why ________ is culturally taboo.

Answer 29

Recessive Alleles Incest

Question 30

Heterozygotes are carries or ________alleles?

Answer 30

recessive

Question 31

Cystic Fibrosis is a ________ trait the occurs in primarily __________. 1 in 25 _______ are a carrier (Aa). The allele codes for a membrane protein that transports Cl across the cell membrane. Results in thick mucus around cells that builds up in the lungs, pancreas and digestive tract causing bacterial infections. Without treatment children die before age 5 and with treatment the life expectancy is past the late 20s.

Answer 31

recessive whites of European descent

Question 32

Tay Sacs is a ________trait that occurs mainly in Ashkenazi Jews and Cajuns (Louisiana) with a non-functional enzyme failing to break down lipids in brain cells. Fat collects in cells destroying their function. Symptoms include seizures, blindness, muscular degeneration. 1 in 3600 births are affected and child normally dies before age 5.

Answer 32

Recessive

Question 33

Phenylketonuria (PKU) is an autosomal recessive inherited disease. Describe what is affected biologically and the symptoms.

Answer 33

Phenylketonuria (PKU) is a rare, inherited metabolic disorder where the body can't process the amino acid phenylalanine, which is a building block of protein found in most foods. If untreated, high levels of phenylalanine can damage the brain and lead to intellectual disability. Symptoms can include developmental delays, light skin and hair, and a musty odor.

Question 34

What do recessive alleles stick around in a popultion?

Answer 34

The dominant phenotype masks their presence in heterozygotes, meaning individuals with one dominant and one recessive allele will express the dominant trait. Carrying one copy of a recessive allele provides a selective advantage Mutation, the process by which new alleles arise, can continually introduce recessive alleles into the population, counteracting any selection against them.

Question 35

In tropical Africa where malaria is common, there is a Heterozygote Advantage. What are the results of a malaria infection for the following Sickle Cell Trait carriers. 1. Homozygous Dominant Individuals 2. Homozygous Recessive Individuals 3. Heterozygote Carriers

Answer 35

1. Die of Malaria 2. Die of Sickle Cell Anemia 3. Relatively Free of Both Issues

Question 36

Huntington's Chorea is an Autosomal Dominant Trait. What are the symptoms?

Answer 36

Build up of Huntingtin protein in the brain causing cell death. Memory less, muscle tremors, jerk movement (chorea), starts at age 30-50 with death 10-20 years following.

Question 37

Sickle Cell Anemia is an autosomal recessive inherited disorder. Primarily affecting individuals of African descent with 1 in 400 African Americans affected. What is the mutation?

Answer 37

A substitution of a single amino acid in hemoglobin. Deforms red blood cells into sickle shapes when oxygen levels are low.

Question 38

What are the chances that two carriers of an autosomal recessive disease will pass on one allele to their offspring? That a child will be affected by the disease?

Answer 38

3/4 1/4

Question 39

Two parents without hemophilia, a sex-linked trait, have a son with hemophilia. What can you determine about their phenotypes?

Answer 39

Hemophilia is an X linked recessive trait. So, Mom would have to be Heterozygous and dad would have a normal/dominant X chromosome since he does not have hemophilia.

Question 40

What are potential benefits of genetic testing?

Answer 40

Diagnosing or confirming genetic conditions Understanding and managing disease risks Guiding treatment decisions Informing family planning

Question 41

What are potential risks of genetic testing?