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Questions and Answers
What is the risk of offspring with male genitalia being affected if the mother is a carrier of an X-linked recessive disorder?
What is the risk of offspring with male genitalia being affected if the mother is a carrier of an X-linked recessive disorder?
Which trait is an example of a sex-limited trait?
Which trait is an example of a sex-limited trait?
What is a key characteristic of sex-influenced traits?
What is a key characteristic of sex-influenced traits?
What does the frequency of recombinations during crossover help determine?
What does the frequency of recombinations during crossover help determine?
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Recurrence risks of multifactorial diseases are affected by which of the following?
Recurrence risks of multifactorial diseases are affected by which of the following?
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Which of the following best describes a frameshift mutation?
Which of the following best describes a frameshift mutation?
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What is the role of RNA polymerase during transcription?
What is the role of RNA polymerase during transcription?
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Which nitrogenous bases are classified as purines?
Which nitrogenous bases are classified as purines?
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What is the complementary base to adenine in a DNA strand?
What is the complementary base to adenine in a DNA strand?
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What does gene splicing involve?
What does gene splicing involve?
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Which of the following is classified as a mutagen?
Which of the following is classified as a mutagen?
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What occurs during the process of DNA replication?
What occurs during the process of DNA replication?
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What does a spontaneous mutation refer to?
What does a spontaneous mutation refer to?
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What is a characteristic of chromosome breakage?
What is a characteristic of chromosome breakage?
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Which of the following describes a deletion?
Which of the following describes a deletion?
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What does the term 'duplication' in chromosome structure refer to?
What does the term 'duplication' in chromosome structure refer to?
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What occurs during an inversion of chromosome segments?
What occurs during an inversion of chromosome segments?
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What is the outcome of a reciprocal translocation?
What is the outcome of a reciprocal translocation?
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In the context of chromosome abnormalities, which of the following describes fragile X syndrome?
In the context of chromosome abnormalities, which of the following describes fragile X syndrome?
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What does the term 'allele' refer to?
What does the term 'allele' refer to?
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What differentiates a homozygous genotype from a heterozygous genotype?
What differentiates a homozygous genotype from a heterozygous genotype?
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What is the phenotype of an individual?
What is the phenotype of an individual?
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Which of the following conditions is caused by a deletion on chromosome 5?
Which of the following conditions is caused by a deletion on chromosome 5?
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Study Notes
Genes and Genetic Diseases
- Genes are the basic units of heredity
- Genes are made of DNA
- DNA is a double helix, made of deoxyribose, phosphate molecules, and four nitrogenous bases: adenine, guanine, cytosine, thymine
- Nucleotides are the building blocks of DNA
- Proteins are made of one or more polypeptides, and amino acids
- Amino acids are coded for by DNA bases (codons)
- DNA replication involves unwinding and unzipping the DNA strand, creating a template strand and complementary base pairing (adenine-thymine; cytosine-guanine)
- DNA contains codes for amino acids.
- Translation utilizes tRNA and ribosomes to synthesize polypeptides
- mRNA moves out of the nucleus and into the cytoplasm
- Genes are spliced (introns removed, exons joined) before migration to the cytoplasm.
Mutations
- Mutations are inherited alterations of genetic material
- Mutations can involve chromosome aberrations, base pair substitutions, and frameshift mutations (insertions or deletions of base pairs).
- Spontaneous mutations occur without exposure to mutagens.
- Mutational hot spots are areas of chromosomes with high mutation rates.
- Mutagens are agents that increase mutation frequency, including radiation and chemicals (nitrogen mustard, vinyl chloride, alkylating agents, formaldehyde, sodium nitrite).
Transcription
- RNA is synthesized from the DNA template using RNA polymerase
- RNA polymerase binds to a promoter site in DNA
- Transcription results in messenger RNA (mRNA)
- RNA polymerase detaches after mRNA is formed
- mRNA moves out of the nucleus into the cytoplasm
- Transcription terminates at a termination sequence.
Gene Splicing
- Introns, non-protein-coding segments in RNA sequences, are removed
- Exons, protein-coding segments in RNA sequences, are joined together
- Splicing occurs before mRNA migrates to the cytoplasm.
Translation
- RNA directs the synthesis of a polypeptide at the ribosome
- tRNA contains an anticodon complementary to the mRNA codon
- Ribosomes move along the mRNA to create an amino acid sequence
- The polypeptide is released into the cytoplasm when a termination sequence is reached.
Chromosomes
- Somatic cells have 46 chromosomes (23 pairs) - diploid cells.
- Gametes have 23 chromosomes - haploid cells.
- Autosomes are the first 22 of the 23 pairs of chromosomes, virtually identical.
- Sex chromosomes are the remaining pair: (XX) for female and (XY) for males.
- Karyotype is a visual representation of chromosomes.
- Meiosis forms haploid cells from diploid cells
- Mitosis forms somatic cells
Chromosome Aberrations
- Euploid cells have a multiple of the normal chromosome number
- Haploid and diploid cells are euploid forms
- Polyploid cells have more than the normal chromosome number
- Triploidy (69 chromosomes); tetraploidy (92 chromosomes) are lethal
- Aneuploidy is a condition in which a somatic cell does not have a multiple of 23 chromosomes.
- Trisomy is having three copies of a chromosome
- Monosomy is having one copy of a chromosome
- Nondisjunction results in an unequal division of chromosomes during mitosis or meiosis, leading to aneuploidy.
- Partial trisomy involves having an extra portion of a chromosome in each cell.
- Chromosomal mosaics have trisomies appearing in some cells, but not others of the body.
Autosomal Aneuploidy (e.g., Down Syndrome)
- Down syndrome is a type of autosomal aneuploidy (trisomy 21)
- Intellectual disability, low nasal bridge, epicanthal folds, protruding tongue, low-set ears, and poor muscle tone
- Risk increases with maternal age above 35 years.
Sex Chromosome Aneuploidy: Turner's Syndrome, Klinefelter's Syndrome
- Turner's syndrome (XO): females with only one X chromosome
- Characteristics include underdeveloped ovaries (sterile), short stature, webbing of the neck, edema, undeveloped breasts.
- Klinefelter's syndrome (XXY): males with at least two X chromosomes, and one Y chromosome.
- Characteristics include male appearance but with develop female-like breasts, small testes (usually sterile), sparse body hair, and long limbs.
Abnormalities in Chromosome Structure
- Chromosome breakage can lead to a variety of structural changes.
- Deletions: loss of DNA (e.g., Cri du chat syndrome – deletion of the short arm of chromosome 5).
- Duplications: repetition of a gene or gene sequence (often less severe than deletions).
- Inversions: reversal of a segment of DNA within a chromosome.
- Translocations: interchange of chromosomal material between nonhomologous chromosomes (can be reciprocal or Robertsonian).
- Fragile sites: areas on chromosomes susceptible to breaks during replication (e.g., fragile X syndrome which contains a site on the long arm of the X chromosome).
Genetics
- Locus: position of a gene along a chromosome
- Allele: different form of a gene at a given locus
- Polymorphism: locus with two or more alleles that occur with appreciable frequency
- Homozygous: identical genes at corresponding loci on a pair of chromosomes
- Heterozygous: different genes at corresponding loci on a pair of chromosomes
- Genotype: genes that an individual possesses
- Phenotype: observable characteristics of an individual Dominant allele: expressed even if only one copy is present
- Recessive allele: expressed only if two copies are present
- Alleles can be codominant
- Mode of inheritance: how genes are passed from parent to offspring
- Principle of Segregation: in a diploid organism, pairs of alleles are separated during gamete production
- Principle of independent assortment: alleles for different traits are distributed independently to gametes
- Pedigree: family tree used to study inheritance patterns
- Recurrence risk: probability that an individual will develop a genetic disease.
- Penetrance: percentage of individuals with a specific genotype who express the expected phenotype.
- Incomplete Penetrance: individual has the gene but doesn't express the disease
- Expressivity: extent of variation in phenotype associated with a given genotype. Can be impacted by modifiers, environment, mutations
- Epigenetics: chemical modifications to DNA or associated proteins can alter gene expression without changing the DNA sequence.
- Genomic imprinting: one parent's imprint of a specific gene is inactive, while the other parent's imprint is active.
- Consanguinity: mating of two related individuals
- Sex-limited traits: only occur in one gender Sex-influenced traits: occur more frequently in one sex over another.
Linkage Analysis and Gene Mapping
- Crossovers during meiosis can create recombinations of linked alleles, used to map their distance on a chromosome
- Marker loci can be used to predict the development of genetic diseases.
Multifactorial Inheritance
- Polygenic traits: affected by several loci
- Multifactorial traits: affected by genetic and environmental factors, threshold of liability
- Recurrence risks change with populations and increase if multiple family members are affected
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Description
Test your knowledge on the fundamentals of genes, DNA structure, and genetic diseases. This quiz covers concepts such as mutations, protein synthesis, and DNA replication processes. Understand the integral relationship between genes and heredity, and explore how mutations can affect genetic information.
