Mendelian Inheritance Quiz
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Questions and Answers

What is the definition of alleles in the context of Mendelian inheritance?

  • Non-genetic factors affecting traits
  • Genes that are always dominant
  • Different genes for the same trait
  • Different versions of the same gene (correct)

    • In which type of inheritance can co-dominance commonly occur?

  • Mendelian inheritance (correct)
  • Sex-linked inheritance
  • Non-allelic gene interaction
  • Autosomal dominant inheritance

    • What kind of inheritance pattern is affected by both parents carrying the gene for a trait?

  • Autosomal recessive inheritance (correct)
  • Sex-linked dominant inheritance
  • Complete dominance inheritance
  • Autosomal dominant inheritance

    • Which of the following is a common autosomal dominant disorder?

    <p>Huntington’s disease (B)</p> Signup and view all the answers

    Which best describes genetic predisposition?

    <p>An increased likelihood of developing certain diseases (A)</p> Signup and view all the answers

    What is the expected probability of an affected individual having a child with haemochromatosis if their partner is normal heterozygous?

    <p>2/4 (D)</p> Signup and view all the answers

    Which of the following statements about Mendelian inheritance is incorrect?

    <p>The inheritance pattern is always consistent. (B)</p> Signup and view all the answers

    What type of inheritance involves traits located on sex chromosomes?

    <p>Sex-linked inheritance (A)</p> Signup and view all the answers

    Which statement is true regarding X-linked disorders?

    <p>Most X-linked disorders result from alleles on the X chromosome. (B)</p> Signup and view all the answers

    What is a common symptom of Fragile X syndrome?

    <p>Long face and large ears (C)</p> Signup and view all the answers

    Which type of point mutation results in a change that does not affect the amino acid sequence?

    <p>Silent mutations (A)</p> Signup and view all the answers

    How are X-linked recessive disorders transmitted?

    <p>Depending on the carrier status of either parent. (D)</p> Signup and view all the answers

    Which of the following is a form of mutation?

    <p>Point mutation (D)</p> Signup and view all the answers

    What is the primary consequence of frameshift mutations?

    <p>Incomplete protein synthesis (B)</p> Signup and view all the answers

    Which condition is NOT classified as an X-linked recessive disorder?

    <p>Cystic fibrosis (C)</p> Signup and view all the answers

    Which point mutation directly results in the formation of a stop codon?

    <p>Nonsense mutations (B)</p> Signup and view all the answers

    Why is it important for the DNA sequence to be preserved?

    <p>Alterations can impact protein function. (D)</p> Signup and view all the answers

    In which scenario would a deletion mutation be expected to have a severe effect?

    <p>Large chunks of DNA are deleted. (A)</p> Signup and view all the answers

    What differentiates a mutant from a wild type organism?

    <p>A mutant has a usual phenotype altered by mutation. (C)</p> Signup and view all the answers

    What is the result of a missense mutation?

    <p>A single amino acid change in the protein (C)</p> Signup and view all the answers

    Which type of mutation involves the exchange of sections of DNA between chromosomes?

    <p>Translocation (A)</p> Signup and view all the answers

    Which of the following is a characteristic of gross mutations?

    <p>They involve large stretches of DNA. (A)</p> Signup and view all the answers

    Which mutation type can lead to the total loss of a gene?

    <p>Deletion (A)</p> Signup and view all the answers

    What is the common outcome of point mutations in general?

    <p>They may cause variability in the DNA sequence among individuals. (D)</p> Signup and view all the answers

    What type of gross mutation is identified when parts of genes exchange with one another?

    <p>Translocation (D)</p> Signup and view all the answers

    What is the main consequence of a frameshift mutation caused by an insertion of extra bases?

    <p>Generation of a stop codon (C)</p> Signup and view all the answers

    Which syndrome is caused by a translocation involving chromosomes 14 and 21?

    <p>Down syndrome (A)</p> Signup and view all the answers

    What type of mutation involves the rotation of a gene leading to its reinserted position in the same chromosome?

    <p>Inversion (B)</p> Signup and view all the answers

    Which condition is characterized by extremely weak muscle tone due to gene duplication?

    <p>Pallister Killian syndrome (B)</p> Signup and view all the answers

    What type of mutation leads to the inversion of genes involved in blood clotting, causing haemophilia A?

    <p>Inversion (D)</p> Signup and view all the answers

    What is the primary mechanism that gene duplication provides during molecular evolution?

    <p>Produces new genetic material (B)</p> Signup and view all the answers

    What protein modification occurs due to the mutation changing CAG to TAG, specifically swapping valine for isoleucine?

    <p>Missense mutation (D)</p> Signup and view all the answers

    What type of DNA damage involves directly harming one of its bases?

    <p>Point damage (B)</p> Signup and view all the answers

    What is one potential consequence of mutations in proto-oncogenes?

    <p>Uncontrolled cell growth (A)</p> Signup and view all the answers

    Which cellular factor typically promotes cell division and growth?

    <p>Proto-oncogenes (C)</p> Signup and view all the answers

    What is the role of the p53 protein in the cell?

    <p>Regulating cell division and apoptosis (D)</p> Signup and view all the answers

    What can result from the backup of DNA repair processes?

    <p>Higher mutation rates (A)</p> Signup and view all the answers

    How can environmental factors contribute to cancer development?

    <p>By causing genome damage that is not repaired (C)</p> Signup and view all the answers

    What is an example of a genetic mutation that can affect proto-oncogene function?

    <p>Point mutation (C)</p> Signup and view all the answers

    Which of the following describes the effect of telomerase activation?

    <p>Prolonged cell division (B)</p> Signup and view all the answers

    What is the primary function of the p53 gene?

    <p>To trigger the apoptosis program (D)</p> Signup and view all the answers

    Which cancer types are associated with damage to the p53 gene?

    <p>Sarcomas and leukaemias (D)</p> Signup and view all the answers

    What is the role of telomerase in cancer cells?

    <p>It maintains telomere length (C)</p> Signup and view all the answers

    What is the estimated lifetime risk of developing breast cancer for women?

    <p>1 in 8 (C)</p> Signup and view all the answers

    Which genes are primarily responsible for familial breast cancer?

    <p>BRCA1 and BRCA2 (C)</p> Signup and view all the answers

    What genetic condition increases the risk of colorectal cancer?

    <p>Lynch syndrome (B)</p> Signup and view all the answers

    What effect does prophylactic mastectomy have on breast cancer risk?

    <p>It reduces the risk by 90% (A)</p> Signup and view all the answers

    Familial adenomatous polyposis is inherited in what pattern?

    <p>Autosomal dominant (A)</p> Signup and view all the answers

    Flashcards

    Mendelian Inheritance

    A type of inheritance pattern where a single gene trait or disorder is passed down from parent to offspring.

    Punnett Square

    A visual tool used to predict the possible genotypes and phenotypes of offspring from a cross.

    Alleles

    Different versions of the same gene. They determine specific traits.

    Dominant Inheritance

    A type of inheritance where one allele masks the expression of another allele.

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    Co-dominance

    A type of inheritance where two dominant alleles are expressed simultaneously.

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    Epistasis

    A type of inheritance where the expression of one gene is influenced by one or more other genes.

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    Autosomal Inheritance

    A type of inheritance involving genes located on autosomes, which are non-sex chromosomes.

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    Sex-linked Inheritance

    A type of inheritance involving genes located on the sex chromosomes, X and Y.

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    What are sex-linked disorders?

    Sex-linked disorders are caused by genes located on the sex chromosomes (X and Y). Most are X-linked because the X chromosome is larger.

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    How are X-linked recessive disorders inherited?

    X-linked recessive disorders are passed down through families; they are more common in males because they only have one X chromosome. Females have two X chromosomes, so they can be carriers but not always show symptoms.

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    What is Fragile X syndrome?

    These disorders cause intellectual disability, a long face, large ears, and testes. They occur due to an expansion of CGG triplets on the X chromosome.

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    What is Duchenne muscular dystrophy?

    These disorders cause muscle weakness, early onset, and progression to wheelchair confinement and early death.

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    What are X-linked dominant disorders?

    X-linked dominant disorders are very rare because they affect both males and females equally, making it more likely they will be eliminated from the gene pool.

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    What are mutations?

    Mutations are changes to the DNA sequence of the genome.

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    What are wild-type and mutant organisms?

    Wild-type organisms have the usual phenotype for their species, while mutants display a change caused by a mutation.

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    What types of mutations exist?

    Point mutations involve changes at a specific base in the DNA sequence. Gross mutations affect larger stretches of DNA.

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    Silent Mutation

    A type of point mutation where a single nucleotide is changed, but the resulting amino acid sequence remains the same.

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    Frameshift Mutation

    A mutation that shifts the reading frame of a gene due to the insertion or deletion of a nucleotide, leading to a drastically different protein.

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    Missense Mutation

    A point mutation where a single nucleotide change leads to a different amino acid being incorporated into the protein.

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    Nonsense Mutation

    A point mutation that introduces a premature stop codon, resulting in a truncated and non-functional protein.

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    Gross Mutation

    A type of mutation that involves a large alteration to a DNA molecule, often affecting a substantial portion of the DNA sequence.

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    Deletion Mutation

    A gross mutation where a segment of DNA is removed from a chromosome. This can lead to the loss of a gene or part of a gene.

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    Insertion Mutation

    A gross mutation where a segment of DNA is inserted into a chromosome at a different location, potentially disrupting gene function.

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    Translocation Mutation

    A gross mutation where a segment of DNA is moved from one chromosome to another, potentially altering gene expression.

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    Duplication Mutation

    A type of mutation where an extra copy of a gene is produced.

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    Point Mutation

    A mutation where a single nucleotide is changed, resulting in the substitution of one amino acid for another.

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    Base pair excision repair

    The process of removing and replacing a damaged or incorrect base within the DNA molecule.

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    Nucleotide excision repair

    A type of DNA repair mechanism where a damaged DNA segment, often containing several bases, is excised and replaced with a new segment.

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    Mismatch repair

    A system that corrects mismatched base pairs that were not identified and corrected during DNA replication.

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    Proto-oncogenes

    Genes that regulate normal cell growth and division, and can become oncogenes when mutated.

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    p53

    A key regulator of cell cycle progression and a critical tumor suppressor gene.

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    Amplification mutation

    A type of mutation that involves the creation of multiple copies of a proto-oncogene, resulting in increased gene expression.

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    Tumor suppressor gene

    A gene that, when mutated, can lead to an increased risk of developing cancer. These genes normally function to suppress tumor growth by promoting cell death or halting the cell cycle.

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    p53 protein

    A protein that plays a critical role in regulating the cell cycle and preventing uncontrolled growth. It can induce cell death (apoptosis) if DNA damage is detected.

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    Telomeres

    Protective caps at the ends of chromosomes that prevent degradation and fusion. They shorten with each cell division.

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    Telomerase

    An enzyme that adds DNA sequences to telomeres, essentially lengthening them. This helps maintain chromosome integrity and potentially contributes to cellular immortality.

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    Lynch syndrome

    A type of inherited disorder that increases the risk of developing cancers, particularly in the colon and rectum. It is associated with mutations in genes involved in DNA repair.

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    Familial adenomatous polyposis

    A hereditary condition characterized by the development of numerous polyps in the colon, significantly increasing the risk of colorectal cancer.

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    BRCA1 gene

    A gene involved in DNA repair and cell cycle regulation. Mutations in this gene can significantly increase the risk of breast and ovarian cancers.

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    BRCA2 gene

    A gene involved in DNA repair and cell cycle regulation. Mutations in this gene can significantly increase the risk of breast and ovarian cancers.

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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!

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