Lecture 23: It's in the genes

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Questions and Answers

What happens to the effect of recessive alleles in the presence of dominant alleles?

They are destroyed

They are amplified

They are enhanced

They are masked (correct)

What is a characteristic of recessive alleles?

They are never found in proteins

They can be more common in some populations (correct)

They are always rare in populations

They always cause genetic diseases

What is the result of co-dominance?

The effect of one allele is masked

Two different alleles and phenotypes are expressed equally (correct)

One allele is dominant over the other

The alleles cancel each other out

How many alleles are there for the ABO gene?

3 alleles Signup and view all the answers

What is an example of an autosomal recessive trait?

Dry earwax Signup and view all the answers

What is the relationship between the IA and IB alleles?

IA and IB are codominant Signup and view all the answers

What type of inheritance is associated with the AB blood type?

Co-dominant Signup and view all the answers

What is the genotype of an individual with an A blood type?

IAIA or IAi Signup and view all the answers

What is the function of the protein encoded by the gene ABCC11?

It is a protein transporter Signup and view all the answers

What is the effect of the recessive allele of the gene ABCC11?

It codes for a non-functioning protein Signup and view all the answers

What is the phenotype of an individual with the ii genotype?

O blood type Signup and view all the answers

What is the phenotype associated with the recessive allele of the gene ABCC11?

Dry earwax Signup and view all the answers

What is the difference between dominant and recessive alleles?

Dominant alleles mask the effect of recessive alleles Signup and view all the answers

What is the definition of a genotype?

The combination of alleles for a particular gene Signup and view all the answers

What is the relationship between genotype and phenotype?

Genotype determines phenotype, but not vice versa Signup and view all the answers

What is an example of a dominant phenotype?

A blood type Signup and view all the answers

What is the major symptom of sickle cell disease?

Severe pain from obstruction of blood flow Signup and view all the answers

What is the advantage of being heterozygous for the sickle cell trait?

Greater resistance to malaria Signup and view all the answers

What is the purpose of a pedigree?

To show the presence or absence of a trait in a family Signup and view all the answers

What can be inferred about Anne's genotype?

She is heterozygous Signup and view all the answers

Why are malaria-infected red blood cells removed by macrophages?

Because they tend to sickle Signup and view all the answers

What is the relationship between sickle cell disease and malaria?

Heterozygous individuals have greater resistance to malaria Signup and view all the answers

What is the allele for dry earwax?

e Signup and view all the answers

What is the genotype of the mother in the dihybrid cross?

EeBb Signup and view all the answers

What is the effect of being a heterozygote for the sickle cell allele?

The person will be a carrier of the sickle cell allele. Signup and view all the answers

What is the difference between a normal red blood cell and a sickle cell red blood cell?

The shape of the cell. Signup and view all the answers

Why does the sickle cell allele persist in human populations?

The question is not answered in the passage. Signup and view all the answers

What is the genotype of the father in the dihybrid cross?

EeBb is not provided in the passage. Signup and view all the answers

What is the result of the mutation in the HBB gene?

An abnormal haemoglobin beta subunit. Signup and view all the answers

What is the likelihood that the child would have dry earwax and perceive PTC to be bitter?

1/8 Signup and view all the answers

What is the characteristic of the normal HTT protein?

It has a normal number of trinucleotide repeats Signup and view all the answers

Why does the abnormal HTT allele persist in human populations?

Because patients may have children before diagnosis Signup and view all the answers

What is the worldwide prevalence of Huntington's disease in Western countries?

5-7 people per 100,000 Signup and view all the answers

What is the genotype of a parent if their child has a 50% chance of inheriting Huntington's disease?

Hh Signup and view all the answers

What is the age range at which symptoms of Huntington's disease typically manifest?

30-45 years Signup and view all the answers

What is unique about the incidence of Huntington's disease in the Lake Maracaibo region, Venezuela?

It is one of the highest in the world Signup and view all the answers

What is the difference between the normal and mutant alleles of the HTT gene?

The mutant allele has additional CAG repeats Signup and view all the answers

Why do affected individuals typically pass away 20 years after the onset of symptoms?

Because the disease progresses rapidly Signup and view all the answers

Study Notes

Alleles and Genotypes

Not all alleles are normal; some may be recessive or have a reduced function
Heterozygous genotypes have two different alleles, e.g., IAi
Recessive alleles can be expressed if an individual is homozygous recessive, e.g., ii

Dominant and Recessive Alleles

Dominant alleles mask the effect of recessive alleles
Recessive alleles can retain some normal function, but at a reduced capacity or be completely dysfunctional
Recessive alleles are not necessarily rare in a population
Recessive alleles don't necessarily cause genetic diseases

Co-dominance

Co-dominance occurs when two different alleles and phenotypes are expressed equally
Examples: AB blood type, Sickle cell anemia

Inheritance Patterns

Autosomal recessive: dry earwax, Hemochromatosis, Sickle cell disease
Autosomal dominant: bitter taste perception, wet earwax, Huntington's disease
Co-dominant: AB blood type, Sickle cell anemia
Incomplete dominance: Sickle cell anemia
X-linked recessive: g6pd deficiency, Red-green color blindness, Haemophilia A
X-linked dominant: Rett's syndrome
Y-linked: "Webbed toes"

Earwax Type

Controlled by the gene ABCC11 on chromosome 16
Encodes for a protein transporter
Two alleles: dominant allele codes for a functioning protein, recessive allele codes for a non-functioning protein
Recessive phenotype: dry earwax, dominant phenotype: wet earwax

ABO Blood Group

Three alleles: IA, IB, and i
IA and IB are co-dominant
i allele encodes for an inactive enzyme
Heterozygous genotype: IAi or IBi
Homozygous recessive genotype: ii

Genotype vs Phenotype

Genotype: combination of alleles for a particular gene
Phenotype: observable or measurable characteristic arising from the genotype and its interaction with environmental factors

Dihybrid Cross

Determining the phenotype and genotype for two traits
Example: earwax type and bitter taste perception

Sickle Cell Disease

Mutation in HBB gene resulting in abnormal haemoglobin beta subunit
Heterozygotes exhibit the sickle cell trait and are carriers of the abnormal allele
Co-dominant phenotype: mixture of normal and sickle red blood cells
Incomplete phenotype: lower blood oxygen levels

Why Sickle Cell Allele Persists

Heterozygous individuals have greater resistance to malaria
Malaria infected red blood cells tend to sickle and are removed by macrophages

Pedigrees

A family tree indicating the presence or absence of a trait for each member
Conventions: unaffected male, unaffected female, affected male, affected female

Huntington's Disease

Autosomal dominant disorder
Mutant alleles characterized by additional CAG repeats
Normal alleles encode for a normal HTT protein
Abnormal HTT allele prone to misfolding

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Description

This quiz covers the basics of genetics, including heterozygous genotypes, recessive alleles, and their effects on phenotypes.