Genetics: Monogenic Diseases Overview

Questions and Answers

What is the primary cause of monogenic diseases?

Chromosomal abnormalities

Multiple gene mutations

Point mutations in single genes (correct)

Environmental factors

Which of the following publications helped to catalog monogenic diseases?

Principles of Genetics

Mendelian Inheritance (correct)

Genetic Disorders of the World

The Human Genome Project

How many recognized monogenic diseases are attributed to mutations in known genes?

1200

2000

2800 (correct)

1777

What percentage of the genome is known to encode proteins?

1.4% Signup and view all the answers

What does it mean for a gene to be a 'modifier' in monogenic diseases?

It has minor effects on disease phenotype Signup and view all the answers

Approximately how many genes are suspected to have a genetic basis but have unknown causative genes?

2000 Signup and view all the answers

Who was Victor McKusick?

A medical geneticist who cataloged monogenic diseases Signup and view all the answers

What online resource was developed to manage an increasing number of described monogenic diseases?

OMIM Signup and view all the answers

What is indicated by the need to split the collection of monogenic diseases into more than two volumes?

An extensive rise in the number of recognized diseases Signup and view all the answers

What percentage of genes in the human genome is estimated to have a known function?

Majority of genes have known functions Signup and view all the answers

What ratio of phenotypes is expected in the second filial generation from a dihybrid cross according to Mendel's experiments?

9:3:3:1 Signup and view all the answers

In Mendel's law of independent assortment, what is true about the transmission of different gene pairs?

They are transmitted independently if located on different chromosomes. Signup and view all the answers

What characterizes a backcross?

Crossing between heterozygotes and homozygotes. Signup and view all the answers

What term is used for the position of a gene on a chromosome?

Locus Signup and view all the answers

How many alleles can exist for a single gene, as illustrated by the beta globin gene example?

More than two Signup and view all the answers

Which of the following best describes monogenic diseases?

Result from a mutation in a single gene. Signup and view all the answers

What does the genotype 'S' in the beta globin gene represent?

A mutation leading to sickle cell anemia. Signup and view all the answers

What is indicated by phenotypic ratios in Mendel's experiments?

The probability distribution of different phenotypes in progeny. Signup and view all the answers

What type of cross results in a 1:2:1 phenotypic ratio?

Self cross between two heterozygotes Signup and view all the answers

Which of the following describes a dihybrid?

An individual heterozygous for both characters. Signup and view all the answers

What percentage of known hereditary diseases are associated with specific genes according to the provided information?

11% Signup and view all the answers

Which plant species did Mendel choose for his experiments?

Pisum sativum Signup and view all the answers

What was the observed phenotypic ratio in the second filial generation (F2) according to Mendel’s experiments?

3:1 Signup and view all the answers

Which concept states that members of a gene pair separate into different gametes?

Law of segregation Signup and view all the answers

What term did Mendel use to refer to what we now call genes?

Hereditary particles Signup and view all the answers

In Mendel’s experiments, which phenotype dominated the first filial generation (F1)?

The dominant phenotype only Signup and view all the answers

What hypothesis suggests that different shapes of a phenotype correspond to different appearances of hereditary particles?

Genes are in pairs Signup and view all the answers

Which of the following is NOT one of Mendel's five core hypotheses?

Genetic variation occurs through mutations Signup and view all the answers

What method did Mendel use to ensure he knew which parent was male and which was female?

Removing anthers of one plant Signup and view all the answers

How did Mendel ensure his parental lines were pure before beginning experiments?

By using inbred populations Signup and view all the answers

What term describes individuals that carry two identical alleles at the same locus?

Homozygous Signup and view all the answers

Which genotype indicates someone is a carrier for sickle cell anemia?

beta A, beta S Signup and view all the answers

Which of the following describes the phenotype?

The observable feature of an individual Signup and view all the answers

What defines a proband in genetic analysis?

The first affected individual used in the analysis Signup and view all the answers

What character trait is expressed in individuals with at least one copy of a defective gene?

Dominant Signup and view all the answers

In the context of sickle cell anemia, what does the term recessive imply?

Both copies of the defective alleles must be present to express symptoms Signup and view all the answers

What is a compound heterozygote?

An individual with two different mutant alleles Signup and view all the answers

Which blood group is an example of codominance?

AB group Signup and view all the answers

What does the genotype for an individual with sickle cell anemia typically look like?

beta S, beta S Signup and view all the answers

What kind of individual is classified as a healthy carrier?

A heterozygote showing no symptoms of disease Signup and view all the answers

Study Notes

Monogenic Diseases Overview

Monogenic diseases are hereditary conditions caused by mutations in a single gene, generally point mutations.
Pathogenesis in these diseases is primarily attributable to one mutated gene, although modifiers may involve other genes with minor effects.
Only 1.4% of the human genome encodes proteins, approximately 22,000 genes identified.

Classification and Recognition of Monogenic Diseases

Medical geneticist Victor McKusick initiated the collection of monogenic disease descriptions, leading to his publication "Mendelian Inheritance."
Over time, this collection expanded significantly, necessitating online accessibility via OMIM (Online Mendelian Inheritance In Man).
Around 2800 monogenic diseases are linked to mutations in known genes.
An additional 1777 diseases have known gene loci, but unidentified causative genes.
Nearly 2000 diseases have suspected genetic bases without knowledge of loci or genes.

Mendelian Genetics

Gregor Mendel conducted foundational experiments with Pisum sativum (pea plants) in the 19th century identifying basic principles of inheritance.
He established concepts such as inheritance patterns, dominant and recessive traits through systematic crossing of pea plants.
Mendel's law of uniformity states that crossing two homozygotes results in a uniform F1 generation that is heterozygous.
The law of segregation explains how gene pairs separate into gametes, creating predictable ratios in offspring.
The law of independence states that different gene pairs assort independently during gamete formation.

Key Genetic Concepts

Locus: The specific position of a gene on a chromosome.
Alleles: Variants of a gene, such as normal beta globin and mutated versions associated with conditions like sickle cell anemia.
Genotype: The genetic makeup of an individual; e.g., heterozygous (beta A, beta S) or homozygous (beta S, beta S).
Phenotype: Observable traits influenced by genotype.
Carrier: A healthy heterozygote who does not express symptoms but can pass on the recessive trait.
Proband: The first affected individual in a genetic analysis, often denoted in family trees.

Types of Genetic Inheritance

Dominant Inheritance: Expressed with just one faulty allele; causes phenotype in heterozygotes.
Recessive Inheritance: Requires two copies of the defective gene to manifest the disease.
Codominance: A heterozygous state expresses phenotypes distinct from both homozygous states, evident in blood types (e.g., AB blood group).

Summary of Mendel's Hypotheses

Mendel proposed five main concepts on heredity:
- Existence of genes as hereditary particles.
- Genes appear in pairs as alleles.
- Gametes contain one allele from each gene pair.
- Equal proportions of alleles are distributed in gametes.
- Random fertilization occurs during zygote formation.

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Description

Explore the fundamentals of monogenic diseases in this quiz. Learn about the inheritance patterns and the role of point mutations in single-gene disorders. This lesson will provide a clear understanding of how these genetic conditions manifest and how they are categorized.