Chapter 02: Genes and Genetic Diseases

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Questions and Answers

What is the primary function of DNA polymerase during DNA replication?

It catalyzes the formation of ribonucleic acid.

It transports amino acids to ribosomes.

It assists in splicing mRNA before it leaves the nucleus.

It adds bases to the new DNA strand and performs proofreading functions. (correct)

Which statement accurately describes the structure of RNA compared to DNA?

RNA has thymine as one of its bases.

RNA is single-stranded and contains uracil. (correct)

RNA is composed of a double helix structure.

RNA contains deoxyribose sugar.

What term describes a sequence of nucleotides that codes for proteins without being excised?

Introns

Mutagens

Exons (correct)

Codons

How many pairs of chromosomes do humans possess?

23 pairs Signup and view all the answers

Which term refers to a mutation-causing substance?

Mutagen Signup and view all the answers

What is the approximate mutation rate per gene per generation in humans?

$1.1 imes 10^{-8}$ Signup and view all the answers

In which cellular structures does translation take place?

Ribosomes Signup and view all the answers

What kind of cells are haploid in humans?

Gametes Signup and view all the answers

Which of the following is directly involved in the process of transcription?

DNA Signup and view all the answers

Which base is found in RNA but not in DNA?

Uracil Signup and view all the answers

Which of the following correctly describes aneuploidy?

Somatic cells having a variation from multiples of 23 chromosomes Signup and view all the answers

What is the recurrence risk for autosomal dominant diseases?

50% Signup and view all the answers

Which chromosome abnormality is known to cause Down syndrome?

Trisomy of chromosome 21 Signup and view all the answers

In classic autosomal dominant pedigrees, which observation is typically not seen?

Skipped generations Signup and view all the answers

Which of the following is a characteristic of X-linked recessive diseases?

Skipped generations are common Signup and view all the answers

What defines a sex-influenced trait?

Occurs more often in one gender than the other Signup and view all the answers

What is the primary consequence of aneuploidy compared to polyploidy?

Aneuploidy is more common in humans Signup and view all the answers

What role does genomic imprinting play in genetic expression?

It affects expression depending on the parent of origin Signup and view all the answers

Which statement about X inactivation is accurate?

One X chromosome in females is inactivated Signup and view all the answers

What is indicated by incomplete penetrance of a gene?

The gene is expressed variably among individuals Signup and view all the answers

What occurs during meiosis I that can lead to genetic diversity?

Crossover Signup and view all the answers

What does the frequency of recombinations between loci on the same chromosome indicate?

The map distance between the loci Signup and view all the answers

Which type of traits are influenced by multiple loci and environmental factors?

Polygenic traits Signup and view all the answers

What term is used to describe the genetic condition that may develop after crossing a specific threshold of liability?

Threshold disease Signup and view all the answers

What was one major goal of the Human Genome Project?

To find the locations of all human genes Signup and view all the answers

How are recurrence risks for multifactorial diseases influenced by family history?

They increase with the severity of the disease in the proband. Signup and view all the answers

What defines a marker locus in relation to disease prediction?

It is closely linked to a disease-gene locus. Signup and view all the answers

What is the outcome of empirical risk estimation in multifactorial diseases?

It estimates recurrence risks based on family observation. Signup and view all the answers

What happens to recurrence risks for multifactorial diseases as the relationship to affected relatives becomes more distant?

They decrease rapidly. Signup and view all the answers

Which of the following best describes multifactorial inheritance?

It includes both genetic and environmental influences. Signup and view all the answers

Study Notes

Genes and Genetic Diseases

Genes are the fundamental units of inheritance comprised of DNA, located on chromosomes.
DNA consists of deoxyribose, phosphate, and four nitrogenous bases, forming a double helix structure.
The sequence of DNA bases encodes amino acids, which are the building blocks of proteins, specified by triplet codons.
DNA replication occurs through complementary base pairing, where a single DNA strand serves as a template.
DNA polymerase plays a crucial role in replication, adding new bases and proofreading for errors.
Mutations are inherited alterations in the genetic material, induced by mutagens.
The human mutation rate is approximately 1.1 x 10^-8 per gene per generation, variable across different loci.
RNA, involved in transcription and translation, is similar to DNA but has a ribose sugar and uracil instead of thymine.
Transcription produces messenger RNA (mRNA) from DNA, while translation synthesizes polypeptides in ribosomes, utilizing mRNA and transfer RNA (tRNA).

Chromosomes

Human cells are categorized as diploid somatic cells and haploid gametes, having 23 chromosome pairs.
Among the 23 pairs, 22 are autosomes and one pair is sex chromosomes: females possess two X chromosomes, and males have one X and one Y chromosome.
A karyotype displays chromosomes in an ordered arrangement based on size and centromere position.
Chromosome abnormalities occur in about 1 in 150 live births and are a primary cause of intellectual disabilities and miscarriages.
Polyploidy in humans may involve triploidy or tetraploidy, both conditions are generally lethal.
Aneuploidy occurs due to nondisjunction, where cells have an abnormal number of chromosomes, leading to trisomy or monosomy.
Down syndrome results from trisomy of chromosome 21 and affects 1 in 800 live births, with increased likelihood in older mothers.
Most sex chromosome aneuploidies cause milder effects compared to autosomal aneuploidies, including Turner’s syndrome and Klinefelter's syndrome.
Chromosome structural abnormalities can include deletions, duplications, inversions, and translocations.

Elements of Formal Genetics

Mendelian traits are influenced by single genes located at specific loci on chromosomes.
Alleles are different gene forms at the same locus; individuals may be homozygous or heterozygous.
An individual’s genotype defines their genetic composition, while the phenotype results from genotype-environment interactions.
In heterozygotes, dominant alleles mask recessive ones; recessivity requires two copies for expression.

Transmission of Genetic Diseases

Genetic diseases are typically classified into autosomal dominant, autosomal recessive, or X-linked recessive inheritance patterns.
Pedigree charts assist in understanding inheritance patterns; autosomal dominant traits do not skip generations.
Recurrence risks indicate the probability of having an affected child, consistent across offspring for single-gene diseases.
Autosomal dominant conditions have a recurrence risk of about 50%.
Germline mosaicism can raise recurrence risks as unaffected parents may still produce affected offspring due to mutations in germline cells.
Both males and females are equally likely to manifest and pass on autosomal dominant diseases.
Many genetic conditions have a delayed onset and may demonstrate incomplete penetrance and variable expressivity.
Genomic imprinting, influenced by methylation, leads to expression differences based on parental transmission.
Epigenetics involves heritable changes that affect gene expression without altering DNA sequences.
Most autosomal recessive diseases occur in offspring whose parents are both carriers, with a 25% recurrence risk.
Consanguinity is common in families with autosomal recessive diseases and increases when diseases are rare.
Carrier detection tests are available for numerous autosomal recessive conditions.

Linkage Analysis and Gene Mapping

Crossover during meiosis I can lead to allele recombination, allowing for the calculation of map distances between loci.
Marker loci closely linked to disease-gene loci can predict genetic disease susceptibility.
The Human Genome Project aimed to map human genes and sequence human DNA, achieving the identification of over 4,000 Mendelian disorders.

Multifactorial Inheritance

Polygenic traits arise from multiple loci' combined effects, influenced further by environmental factors, termed multifactorial inheritance.
Many multifactorial traits have a liability threshold; crossing this threshold can trigger disease expression.
Empirical risks for multifactorial diseases are based on family studies, higher when multiple family members are affected or when the condition is severe.
Recurrence risks diminish rapidly with increasing familial distance of affected individuals.

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Description

Test your understanding of genetics and genetic diseases with this quiz based on Chapter 02 of Huether's 'Understanding Pathophysiology'. Explore the role of DNA, RNA, and how genetic information is inherited at the molecular level. Perfect for students diving into the complexities of genes!