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Questions and Answers
What is the primary function of deoxyribonucleic acid (DNA) within an organism?
What is the primary function of deoxyribonucleic acid (DNA) within an organism?
How are hereditary disorders primarily transmitted?
How are hereditary disorders primarily transmitted?
Which of the following correctly describes the structure of a gene?
Which of the following correctly describes the structure of a gene?
What term refers to the observable traits of an organism?
What term refers to the observable traits of an organism?
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Which component constitutes the backbone of a DNA strand?
Which component constitutes the backbone of a DNA strand?
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What are exons within a gene?
What are exons within a gene?
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What is the classification for disorders caused by mutations in mitochondrial genes?
What is the classification for disorders caused by mutations in mitochondrial genes?
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What does the term 'locus' refer to in genetics?
What does the term 'locus' refer to in genetics?
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What is the consequence of a deletion in a chromosome?
What is the consequence of a deletion in a chromosome?
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Which type of translocation involves the fusion of two acrocentric chromosomes?
Which type of translocation involves the fusion of two acrocentric chromosomes?
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What is a hallmark symptom of Ring Chromosome 20 syndrome?
What is a hallmark symptom of Ring Chromosome 20 syndrome?
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Which structural abnormality is characterized by the flipping or reversing of a chromosome segment?
Which structural abnormality is characterized by the flipping or reversing of a chromosome segment?
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How can duplications affect genetic material?
How can duplications affect genetic material?
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What is a key characteristic of reciprocal translocation?
What is a key characteristic of reciprocal translocation?
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Which type of chromosomal abnormality is least likely to have severe consequences?
Which type of chromosomal abnormality is least likely to have severe consequences?
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What can result from an interstitial deletion?
What can result from an interstitial deletion?
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What is the term for having an exact multiple of the haploid number of chromosomes?
What is the term for having an exact multiple of the haploid number of chromosomes?
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Which of the following conditions is a specific type of aneuploidy characterized by having an extra copy of a single chromosome?
Which of the following conditions is a specific type of aneuploidy characterized by having an extra copy of a single chromosome?
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What is the main difference between aneuploidy and polyploidy?
What is the main difference between aneuploidy and polyploidy?
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What is a common cause of aneuploidy due to failure of chromosomes to separate during cell division?
What is a common cause of aneuploidy due to failure of chromosomes to separate during cell division?
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In which syndrome do females typically have only one X chromosome?
In which syndrome do females typically have only one X chromosome?
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What is the phenomenon called when an individual has two or more distinct cell populations with different chromosome numbers?
What is the phenomenon called when an individual has two or more distinct cell populations with different chromosome numbers?
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What specific type of aneuploidy involves a loss of one chromosome from a pair?
What specific type of aneuploidy involves a loss of one chromosome from a pair?
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What condition refers to the presence of three complete sets of chromosomes in an organism?
What condition refers to the presence of three complete sets of chromosomes in an organism?
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What is the primary consequence of reciprocal translocations in chromosomes?
What is the primary consequence of reciprocal translocations in chromosomes?
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Which condition may result from an isochromosome of one X chromosome?
Which condition may result from an isochromosome of one X chromosome?
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How is the cytogenetic type of regular Down's syndrome primarily caused?
How is the cytogenetic type of regular Down's syndrome primarily caused?
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What percentage of Down’s syndrome cases results from translocation?
What percentage of Down’s syndrome cases results from translocation?
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Which syndrome involves males with a genetic makeup of 47,XXY?
Which syndrome involves males with a genetic makeup of 47,XXY?
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What is the incidence of regular Down's syndrome linked to maternal age for women over 45?
What is the incidence of regular Down's syndrome linked to maternal age for women over 45?
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What is a characteristic feature of mosaic Down's syndrome?
What is a characteristic feature of mosaic Down's syndrome?
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Which chromosomal abnormality is not inherited and caused by cell division errors?
Which chromosomal abnormality is not inherited and caused by cell division errors?
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Study Notes
Introduction to Genetics
- Genetics is the study of genes and heredity, which are the mechanisms by which traits are passed from parents to offspring.
- The genome is the entire genetic material of an organism, including DNA, RNA, and associated proteins.
- DNA is the molecule that carries genetic information and is composed of two linked strands in a double helix shape.
- Each strand has a backbone of alternating sugar (deoxyribose) and phosphate groups.
- Attached to each sugar is one of four nitrogen bases: adenine (A), cytosine (C), guanine (G), or thymine (T).
- The human genome contains approximately 3.2 billion nucleotides.
- A trinucleotide base is called a codon.
- There are 64 codons, with 61 encoding for amino acid synthesis and 3 acting as stop codons.
- Humans have 20 amino acids.
- A gene is a specific sequence of nucleotides within the genome.
- There are about 20,000 protein-encoding genes in the human genome, making up 1.5% of the genome.
- Exons are coding sequences of the gene.
- Introns are non-coding sequences in the gene.
- A locus is the location of a gene on a chromosome.
- Genotype refers to the genetic makeup passed between generations.
- Phenotype refers to the observable characteristics or traits of an organism.
- Hereditary disorders are passed from parents to offspring through gametes, making them familial.
- Congenital means present at birth, but not all genetic disorders are congenital.
Classification of Genetic Disorders
- Genetic disorders are categorized as classical or non-classical.
- Classical genetic diseases include chromosomal disorders, single gene disorders (Mendelian Disorders), and multifactorial disorders.
- Non-classical genetic diseases or single gene disorders with atypical inheritance patterns include mitochondrial gene mutations, triplet repeat mutations, uniparental disomy, genomic imprinting, and gonadal mosaicism.
Chromosomal Disorders
- Approximately 1 in 200 newborn infants is affected by a chromosomal abnormality, with a higher incidence in fetuses that do not survive to term.
- Cytogenetic disorders involve alterations in the number or structure of chromosomes and can affect autosomes or sex chromosomes.
- These abnormalities can be either numerical or structural.
Numerical Abnormalities in Chromosomes
- Euploidy is a normal chromosome count that is an exact multiple of the haploid number (n).
- Aneuploidy is a gain or loss of one or more individual chromosomes.
- Polyploidy involves a gain of entire sets of chromosomes, such as triploidy (3n) and tetraploidy (4n).
- Trisomy refers to an extra copy of a specific autosome, such as in Down syndrome (trisomy 21).
- Monosomy refers to having only one copy of a specific chromosome, like in Turner Syndrome (45,X).
- Non-disjunction, the failure of homologous chromosomes to separate during cell division (meiosis), results in gametes with an extra chromosome (n+1) or one less chromosome (n-1).
- Anaphase lag occurs when a chromosome or chromatid lags behind during division, leading to one normal cell and one with monosomy.
Mosaicism
- Mosaicism refers to the presence of two or more distinct cell populations with different chromosome numbers within an individual's body.
- It can arise from post-zygotic mitotic chromosome errors or pre-existing paternal aneuploidy of meiotic origin.
Structural Abnormalities in Chromosomes
- Structural abnormalities result from chromosomal breakage followed by loss or rearrangement of material.
- These abnormalities include deletions, duplications, inversions, translocations, and isochromosomes.
Deletions
- Deletion involves the loss of a chromosome segment.
- Terminal deletions occur when one break results in the loss of the distal portion.
- Interstitial deletions involve the loss of a segment between two breaks.
Duplications
- Duplication involves the presence of an extra copy of a chromosome segment.
- It can result in an overabundance of certain genes, leading to genetic disorders or variations.
Inversions
- An inversion occurs when a chromosome segment is flipped or reversed in orientation.
- Pericentric inversions involve the centromere, while paracentric inversions do not.
Translocations
- Translocation occurs when two non-homologous chromosomes exchange segments of genetic material.
- Reciprocal translocations involve the exchange of segments between two non-homologous chromosomes.
- Robertsonian translocations involve the fusion of two acrocentric chromosomes, resulting in a single larger chromosome and a smaller fragment.
Isochromosomes
- Isochromosomes are abnormal chromosomes with two identical arms, typically formed due to an error in chromosome division.
Clinical Examples of Chromosomal Abnormalities
Disorders of Autosomal Chromosomes
- Trisomy (21, 18, 13) are responsible for Down syndrome, Edwards syndrome, and Patau syndrome, respectively.
- Deletion, as seen in Cri du chat syndrome, involves chromosome 5.
Trisomy 21 (Down's Syndrome)
- The most common chromosomal disorder, with different cytogenetic types.
- 95% of cases are due to regular trisomy 21, caused by non-disjunction.
- The extra chromosome typically originates from the mother.
- Incidence significantly increases with maternal age.
- Translocation Down's Syndrome represents 4% of cases, with extra chromosomal material attached to chromosome 22 or 14, 15, often familial.
- Isochromosome '21' is rare but can result in Down's syndrome, involving duplication of the long arm of chromosome 21.
- Mosaic Down's Syndrome, accounting for 1% of cases, involves a mix of 47 and 46 chromosomes, with varying symptom severity.
Abnormalities of Sex Chromosomes
- Klinefelter syndrome (47,XXY) affects males with two or more X chromosomes, typically XXY.
- It is not inherited and is caused by a cell division error during fetal development.
- Turner syndrome (45,X0) affects females with a missing or partially missing second X chromosome.
- It occurs in one out of 2,000 female births and is linked to 10% of miscarriages.
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Description
Explore the fundamental concepts of genetics, including the structure of DNA, the human genome, and the role of genes and codons in heredity. This quiz will test your understanding of how traits are passed from parents to offspring and the basic building blocks of genetic information.
