Podcast
Questions and Answers
What is the definition of alleles in the context of Mendelian inheritance?
What is the definition of alleles in the context of Mendelian inheritance?
In which type of inheritance can co-dominance commonly occur?
In which type of inheritance can co-dominance commonly occur?
What kind of inheritance pattern is affected by both parents carrying the gene for a trait?
What kind of inheritance pattern is affected by both parents carrying the gene for a trait?
Which of the following is a common autosomal dominant disorder?
Which of the following is a common autosomal dominant disorder?
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Which best describes genetic predisposition?
Which best describes genetic predisposition?
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What is the expected probability of an affected individual having a child with haemochromatosis if their partner is normal heterozygous?
What is the expected probability of an affected individual having a child with haemochromatosis if their partner is normal heterozygous?
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Which of the following statements about Mendelian inheritance is incorrect?
Which of the following statements about Mendelian inheritance is incorrect?
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What type of inheritance involves traits located on sex chromosomes?
What type of inheritance involves traits located on sex chromosomes?
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Which statement is true regarding X-linked disorders?
Which statement is true regarding X-linked disorders?
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What is a common symptom of Fragile X syndrome?
What is a common symptom of Fragile X syndrome?
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Which type of point mutation results in a change that does not affect the amino acid sequence?
Which type of point mutation results in a change that does not affect the amino acid sequence?
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How are X-linked recessive disorders transmitted?
How are X-linked recessive disorders transmitted?
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Which of the following is a form of mutation?
Which of the following is a form of mutation?
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What is the primary consequence of frameshift mutations?
What is the primary consequence of frameshift mutations?
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Which condition is NOT classified as an X-linked recessive disorder?
Which condition is NOT classified as an X-linked recessive disorder?
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Which point mutation directly results in the formation of a stop codon?
Which point mutation directly results in the formation of a stop codon?
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Why is it important for the DNA sequence to be preserved?
Why is it important for the DNA sequence to be preserved?
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In which scenario would a deletion mutation be expected to have a severe effect?
In which scenario would a deletion mutation be expected to have a severe effect?
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What differentiates a mutant from a wild type organism?
What differentiates a mutant from a wild type organism?
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What is the result of a missense mutation?
What is the result of a missense mutation?
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Which type of mutation involves the exchange of sections of DNA between chromosomes?
Which type of mutation involves the exchange of sections of DNA between chromosomes?
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Which of the following is a characteristic of gross mutations?
Which of the following is a characteristic of gross mutations?
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Which mutation type can lead to the total loss of a gene?
Which mutation type can lead to the total loss of a gene?
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What is the common outcome of point mutations in general?
What is the common outcome of point mutations in general?
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What type of gross mutation is identified when parts of genes exchange with one another?
What type of gross mutation is identified when parts of genes exchange with one another?
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What is the main consequence of a frameshift mutation caused by an insertion of extra bases?
What is the main consequence of a frameshift mutation caused by an insertion of extra bases?
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Which syndrome is caused by a translocation involving chromosomes 14 and 21?
Which syndrome is caused by a translocation involving chromosomes 14 and 21?
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What type of mutation involves the rotation of a gene leading to its reinserted position in the same chromosome?
What type of mutation involves the rotation of a gene leading to its reinserted position in the same chromosome?
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Which condition is characterized by extremely weak muscle tone due to gene duplication?
Which condition is characterized by extremely weak muscle tone due to gene duplication?
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What type of mutation leads to the inversion of genes involved in blood clotting, causing haemophilia A?
What type of mutation leads to the inversion of genes involved in blood clotting, causing haemophilia A?
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What is the primary mechanism that gene duplication provides during molecular evolution?
What is the primary mechanism that gene duplication provides during molecular evolution?
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What protein modification occurs due to the mutation changing CAG to TAG, specifically swapping valine for isoleucine?
What protein modification occurs due to the mutation changing CAG to TAG, specifically swapping valine for isoleucine?
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What type of DNA damage involves directly harming one of its bases?
What type of DNA damage involves directly harming one of its bases?
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What is one potential consequence of mutations in proto-oncogenes?
What is one potential consequence of mutations in proto-oncogenes?
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Which cellular factor typically promotes cell division and growth?
Which cellular factor typically promotes cell division and growth?
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What is the role of the p53 protein in the cell?
What is the role of the p53 protein in the cell?
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What can result from the backup of DNA repair processes?
What can result from the backup of DNA repair processes?
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How can environmental factors contribute to cancer development?
How can environmental factors contribute to cancer development?
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What is an example of a genetic mutation that can affect proto-oncogene function?
What is an example of a genetic mutation that can affect proto-oncogene function?
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Which of the following describes the effect of telomerase activation?
Which of the following describes the effect of telomerase activation?
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What is the primary function of the p53 gene?
What is the primary function of the p53 gene?
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Which cancer types are associated with damage to the p53 gene?
Which cancer types are associated with damage to the p53 gene?
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What is the role of telomerase in cancer cells?
What is the role of telomerase in cancer cells?
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What is the estimated lifetime risk of developing breast cancer for women?
What is the estimated lifetime risk of developing breast cancer for women?
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Which genes are primarily responsible for familial breast cancer?
Which genes are primarily responsible for familial breast cancer?
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What genetic condition increases the risk of colorectal cancer?
What genetic condition increases the risk of colorectal cancer?
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What effect does prophylactic mastectomy have on breast cancer risk?
What effect does prophylactic mastectomy have on breast cancer risk?
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Familial adenomatous polyposis is inherited in what pattern?
Familial adenomatous polyposis is inherited in what pattern?
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Study Notes
Nutritional Biochemistry
- Subject: DIET413/BHCS1019
- Lecturer: Dr Nathaniel Clark FHEA RNutr MRSB
- Email: [email protected]
Previously
- DNA structure: The smallest unit of DNA is a nucleotide. It consists of a nitrogenous base, a pentose sugar, and a phosphate group. Polynucleotide chains are formed through phosphodiester bonds linking the phosphate group and sugar between nucleotides.
- DNA packaging: DNA wraps around histone proteins to condense into chromatin.
- Gene expression: The DNA code undergoes transcription and translation to form functional proteins (phenotype). These processes are highly controlled through enzyme action.
- Mitochondrial DNA: DNA is also found in the mitochondria; it largely produces proteins for respiration.
- DNA mutations and disease; Various disease states are caused by mutations to this part of the genome.
Learning Outcomes
- Genetic inheritance (autosomal and sex-linked inheritance)
- Different types of mutations
- DNA damage repair mechanisms
- Types of cancers
Genotype and Phenotype
- Genotype: The unique DNA sequence of an organism.
- Phenotype: The observable effect of a mutation on an organism.
- Influence: Changes to the genotype can affect the phenotype.
- Inheritance: Inheritable phenotypes are based on the genotype.
Mendelian Inheritance
- Gregor Mendel: His work was foundational to modern genetics.
- Factors: Traits are controlled by factors existing in pairs (genes), one from each parent.
- Dominance/Recessiveness: Each factor can be dominant (heterozygous) or recessive (homozygous).
Mendelian Inheritance - Experiments
- First experiment: Homozygous tall plants (TT) crossed with homozygous short plants (tt) produced all tall plants (F1).
- Second experiment: Hybrid heterozygous tall plants (Tt) crossed, produced 3 tall plants and 1 short plant, demonstrating recessive inheritance.
Mendelian Inheritance - Punnett's Square
- Expression: The inheritance pattern can be visualized using a Punnett Square
- Alleles: Genes responsible for carrying traits are called alleles. (e.g., tall or short)
Mendelian Inheritance - Limitations
- Dominance: Dominance does not apply in every case of contrasting characteristics.
- Blending inheritance: Blending can occur in many crosses.
- Co-dominance: Sometimes two dominant alleles together for blood types result in co-dominance
- Non-allelic gene interaction (epistasis): The presence or absence of other genes can affect gene expression.
Patterns of Inheritance
- Autosomal inheritance: Inheritance via the 22 pairs of autosomes (non-sex chromosomes).
- Sex-linked inheritance: Inheritance via the X and Y sex chromosomes.
- Further classifications of inheritance: autosomal dominant, autosomal recessive, sex-linked dominant, sex-linked recessive.
Autosomal Dominant Inheritance
- Inheritance: A trait or disorder present on the dominant gene.
- Transmission: Easily seen using Punnett's Square.
- Examples: Familial hypercholesterolaemia, Polycystic kidney disease, Huntington's disease.
Autosomal Recessive Inheritance
- Transmission: Depends on whether one or both parents carry the recessive allele.
- Punnett's Square: Both parents carrying the recessive allele can be visually demonstrated using a Punnett Square
- Common disorders; Haemochromatosis, Cystic fibrosis.
Activity
- Haemochromatosis: Calculating the chance of an affected individual having a child with the same condition given different partner genotypes.
Sex-Linked Disorders
- Relevant allele location: Disorders arise from alleles located on the X chromosome. (X-linked).
- X Chromosome size: X chromosomes are greater in size than Y chromosomes.
- X-linked recessive: Transmission depends on whether the mother or father is carrying the allele in this case of this disorder.
X - Linked Recessive Disorders
- Transmission: Transmission depends on whether is the mother or father who carries the allele in this case of this disorder.
- Examples: Fragile X syndrome, Haemophilia, Duchenne muscular dystrophy.
X-linked Dominant Disorders
- Rare: Few common conditions inherited this way.
- Offspring risk: The risk of inheritance for the daughters is different than from sons.
Mutations
- DNA Preservation: DNA sequence is vital for protein function; mutations in the sequence may alter protein function.
- Genome size: The human genome consists of approximately 3 billion base pairs of DNA (distributed across 23 chromosomes)
- Target size: Several mutation-causing sites exist within the genome.
- Types of mutations; chemical and physical agents including ionizing radiation and certain substances from the environment/lifestyle trigger mutations.
Mutants versus Wild Types
- Wild type: The organism with the usual/normal phenotype for the organism
- Mutant: An organism whose usual/normal characteristic has changed due to a mutation.
- Types: Point mutation and gross mutations
Point Mutations
- Basis: Understanding of triplet coding.
- Types: Silent, Frameshift, Missense, Nonsense
Point Mutations – Silent Mutations
- Effect: The wrong nucleotide occurs but doesn't change the amino acid sequence.
- Redundancy: Redundancy in the DNA sequence-codon code.
- Significance: Creates polymorphisms within the same species.
Point Mutations – Frameshift Mutations
- Effect: Deletion or addition of a base changes the triplet code, leading to a disrupted protein amino acid sequence.
- Serious effect: These mutations usually have a serious effect on the encoded protein and are associated with mutant phenotypes.
Point Mutations – Missense Mutations
- Effect: Replacement of a single base, which alters the coding for only one amino acid affecting protein structure minimally.
Point Mutations - Nonsense Mutations
- Effect: A misplaced base causes the triplet code to become a stop codon, leading to the complete truncation of the protein; it is incomplete.
Gross Mutations
- DNA alteration: Substantial alterations to DNA, often extensive stretches of the DNA molecule.
- Types: Deletions, Insertions, Translocation, Inversion, Duplication.
Gross Mutations - Deletions
- Gene loss: Result in a loss of a complete gene or a segment of a gene, or some of the promoter or enhancer elements.
- Consequences: Totally or partially lost proteins or the inability to trigger transcription; examples include Duchenne muscular dystrophy (X - linked recessive disorder).
Gross Mutations - Insertions
- Base insertion: Addition of extra bases from another chromosome segment.
- Consequences; Often cause large frameshift mutations, leading to truncated proteins; example is fragile X syndrome (X-linked recessive disorder).
Gross Mutations - Translocation
- Gene exchange: Involves sections of genes exchanging between one chromosome to another.
- Consequences: Results in hybrid protein formation, leading to Down syndrome and chronic myelogenous leukemia.
Gross Mutations - Inversion
- Gene rotation: Involves rotation and reinsertion of a gene within the same chromosome.
- Types: Paracentric (not involving the centromere) and Pericentric (involving the centromere).
- Consequences: Changes the codon order, making the protein non-functional, sometimes involving blood clotting genes causing haemophilia A.
Gross Mutations - Duplication
- Extra copies: Occurs when a chromosome segment is duplicated.
- Consequences: Can lead to abnormal development. Example; Pallister-Killian syndrome.
Activity - Mutations
- Mutation type and consequences given a DNA sequence.
DNA Damage and Response
- Constant DNA attacks: DNA in cells constantly comes under attack by various agents.
- Types of damage: Direct, point damage or significant backbone disruptions (gross).
- Repair mechanisms: Elaborate processes evolved to address this consistent threat of damage to maintain genome integrity.
Base Pair Excision Repair
- Repair mechanism: A way to repair DNA by recognizing and removing damaged bases like uracil, which cannot form proper pairs with guanine; restoring the correct sequence and proper pairings.
Nucleotide Excision Repair
- Repair mechanism: Repairs DNA damaged by UV-radiation or other carcinogenic substances. This removes the damage inducing segment, and then DNA polymerase rebuilds the gap, followed by sealing using DNA ligase enzyme
Mismatch Repair
- Repair mechanism: Enzymes identify and repair mismatched nucleotides during DNA replication
- Detection/removal: The enzymes recognize the faulty base pairs and remove the incorrect nucleotides, then using the original matching stranded sequence for repair template; DNA polymerase fills the gap, then DNA ligase seals the gap.
Cancer
- Cell regulation: Cell growth and differentiation are usually well regulated by factors such as hormones and growth factors.
- Genome damage: Damage to the genome in specific areas (introns or exons) causes unregulated cell growth leading to the creation of non-functional cells
- Lifestyle Factors: Smoking, diet, obesity, radiation, and viral infections.
- Tumour suppressor genes/oncogenes: Damaged tumor suppressor gene and/or oncogenes cause uncontrolled cell growth and/or loss of regulation that contribute to cancer development
Proto-oncogenes
- Normal role: Involved in normal cell growth and facilitate cell division.
- Conversion to oncogenes: Proto-oncogenes can mutate and convert becoming oncogenes which accelerate cell growth and division.
- Oncogene insertion: Insertion into the genome - retroviruses.
- Tumour suppressor gene deactivation; Deactivation of tumor suppressor genes normally slows cell division and death.
- Telomerase activation: Activation leads to cell growth.
Genetic Mutations in Proto-oncogenes
- Point mutations: These point mutations within regulatory sequences and genes that alter gene function.
- Translocation: Translocation causing rearrangements among genes, alter expression, or create hybrid proteins.
- Amplification: Gene amplification leads to excessive expression of the gene product, which can promote uncontrollable cell division.
p53
- Major regulator: A key regulator involved in cell division and death.
- Apoptosis: Turns on an apoptosis program when cellular stress or damage occurs.
- Tumour suppressor: Encoding gene for p53 functioning as major tumor suppressor gene.
Telomeres
- Protecting chromosome ends: Telomeres protect chromosome ends from degradation and fusion.
- Telomere shortening: Telomeres shorten after each cell division, influencing the lifespan.
- Telomerase's role; this enzyme maintains telomere length; not usually active in normal cells.
- Immortality in cancer cells; cancer cells often acquire the ability to express telomerase, maintaining telomere length and achieving immortality.
Cancer from the Environment
- Environmental factors: Several studies have consistently shown that environmental factors are a major contributor to varied cancer risk.
Breast Cancer (BRCA Genes)
- Most cases are sporadic, only a small fraction are inherited.
- Inherited risk: Some inherited mutations (in BRCA1 or BRCA2 genes) lead to a higher lifetime risk of breast and ovarian cancer.
Colorectal Cancer
- Most cases: Sporadic in nature in the majority of cases
- Genetic predisposition; Accounts for 5-10% of all colorectal cancer; includes Lynch syndrome and Familial Adenomatous Polyposis.
- Inherited risk: Increased risk of cancer in certain locations.
Familial Adenomatous Polyposis (FAP)
- Autosomal dominant: An inherited dominant disorder
- Multiple polyps: Colon cancer development frequently with multiple polyps appearing in early childhood..
- Cancer risk: High risk of colorectal cancer if untreated by age 40.
Summary
- Mendelian inheritance: Describes how traits are inherited and expressed. Mechanisms such as autosomal and sex-linked inheritance and expression.
- DNA alteration: Several DNA modification mechanisms exist, including point mutations and gross mutations.
- Role of DNA repair: Specific DNA repair mechanisms act to maintain the quality of genetic materials and to prevent issues. Various mechanisms exist to combat the effects of damage and assaults.
- Compromised repair; Diseases like cancer result if these repair mechanisms function improperly or fail. Telomerase enzyme, and regulatory genes in the cell cycle can cause cancer if compromised.
Revision Session
- Schedule: This revision session will be split into two parts, one for Dietitians on 9th December and the other for NEH.
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Description
Test your knowledge on Mendelian inheritance concepts, including alleles, genetic disorders, and mutations. This quiz covers various aspects of inheritance patterns and their implications, including examples like Fragile X syndrome. Challenge yourself to see how well you understand the core principles of genetics!
