Biology Chapter 5: Variation Among Individuals
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Questions and Answers

What is the purpose of gel electrophoresis in determining genotypes?

  • To measure the quantity of DNA in a sample
  • To separate DNA and proteins based on charge and size (correct)
  • To enhance the visibility of DNA sequences
  • To replicate DNA for cloning purposes

    • Which genotype will not allow a person to be infected with HIV-1 due to the CCR5 receptor?

  • +/D32 and D32/D32
  • D32/D32 (correct)
  • +/+
  • +/D32

    • If 43 Ashkenazi individuals have a total of 86 allelic copies, how many copies correspond to heterozygous individuals?

  • 18
  • 32
  • 16 (correct)
  • 52

    • What is the frequency of the D32 allele calculated from the Ashkenazi individuals in the example provided?

    <p>0.209 (D)</p> Signup and view all the answers

    Which statement about allele frequencies in general is true?

    <p>Allele frequencies should always add up to 1. (B)</p> Signup and view all the answers

    What is NOT a source of variation among individuals?

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

    Which gene is associated with the ability to detect bitter flavors, including toxins?

    <p>TAS2R38 (A)</p> Signup and view all the answers

    What term describes traits that are not genetically controlled and are not heritable?

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

    What is the reaction norm?

    <p>Phenotypic expression of a single genotype across different environments (C)</p> Signup and view all the answers

    Which statement is true about aversion to cilantro?

    <p>Only partially genetic and influenced by interactions with the environment (A)</p> Signup and view all the answers

    What does a steep slope on a reaction norm graph indicate?

    <p>High phenotypic plasticity of that genotype (C)</p> Signup and view all the answers

    What does phenotypic plasticity refer to?

    <p>The capacity of a genotype to produce different phenotypes in response to environmental conditions (C)</p> Signup and view all the answers

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

    <p>It helps in the formation of point mutations. (B)</p> Signup and view all the answers

    Which of the following describes a transition mutation?

    <p>Change from purine to purine. (B)</p> Signup and view all the answers

    What type of mutation does NOT change the amino acid sequence?

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

    Which type of mutation results from the addition or deletion of nucleotides?

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

    Which of the following correctly describes a nonsense mutation?

    <p>It replaces a codon with a stop codon. (A)</p> Signup and view all the answers

    What role do mutations play in evolution?

    <p>They provide new alleles for natural selection. (A)</p> Signup and view all the answers

    In which case are transitions more likely to occur compared to transversions?

    <p>Within coding regions of DNA. (B)</p> Signup and view all the answers

    Which components make up the structure of DNA?

    <p>Deoxyribose sugar, phosphate group, and nitrogenous bases. (D)</p> Signup and view all the answers

    What characteristic of the genetic code contributes to the redundancy observed?

    <p>Every amino acid is coded by multiple codons. (D)</p> Signup and view all the answers

    Which chromosomal alteration results from meiosis errors creating diploid gametes?

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

    What is the result of a diploid gamete fusing with a haploid gamete?

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

    What reproductive mode do unisexual triploid salamanders use to maintain triploidy?

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

    Which of the following statements about triploids is true?

    <p>They maintain low fertility unless parthenogenetic. (D)</p> Signup and view all the answers

    What is the most common fitness effect of mutations?

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

    What is typically the result of a loss-of-function mutation?

    <p>Deactivation of a gene (B)</p> Signup and view all the answers

    Which type of mutation is known to cause sickle cell anemia?

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

    In which species is polyploid creation as common as point mutation rate?

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

    How can polyploids affect their genome in a way that aids adaptation?

    <p>They increase gene dosage and redundancy. (A)</p> Signup and view all the answers

    What biological characteristic is common in hermaphroditic species that can self-fertilize?

    <p>Presence of both male and female gametes (C)</p> Signup and view all the answers

    What is the primary outcome of gene duplications?

    <p>The accumulation of mutations in the extra copy (D)</p> Signup and view all the answers

    What distinguishes paralogous genes from orthologous genes?

    <p>Paralogous genes arise from gene duplications within a species (D)</p> Signup and view all the answers

    How do gene duplications contribute to the evolution of the globin gene family?

    <p>They allow different globin chains to be produced across developmental stages (A)</p> Signup and view all the answers

    What is a possible consequence of chromosomal inversions?

    <p>Disruption of gene linkage and production of dysfunctional gametes (A)</p> Signup and view all the answers

    What is the definition of retroposition in genetic evolution?

    <p>Insertion of processed mRNA into the genome (B)</p> Signup and view all the answers

    Which of the following describes polyploidy?

    <p>Addition of completely extra sets of chromosomes (D)</p> Signup and view all the answers

    In the context of Drosophila, what is suggested by inversion frequencies varying along a cline?

    <p>They indicate a link to temperature and body size (B)</p> Signup and view all the answers

    During which stages are different chains of globin produced in humans?

    <p>Embryonic, fetal, and adult stages (C)</p> Signup and view all the answers

    What is one potential fate of gene copies resulting from duplication events?

    <p>They can become pseudogenes (C)</p> Signup and view all the answers

    What is formed from two globin clusters in humans?

    <p>Hemoglobin molecules requiring subunits from both clusters (C)</p> Signup and view all the answers

    Flashcards

    Three sources of variation

    The categories through which variation among individuals is derived: genetic, environmental, and genotype-by-environment interaction.

    Genetic Variation

    Differences in individuals’ genes leading to variations in traits, such as the ability to taste PTC.

    TAS2R38 gene

    A gene on chromosome 7 linked to detecting bitter flavors, associated with PTC tasting, with two alleles (PAV and AVI).

    Environmental Variation

    Differences in traits not caused by genetics, influenced by external factors, leading to phenotypic plasticity.

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    Genotype-by-Environment Interaction

    The phenomenon where the effect of an organism's genotype is influenced by the environment, impacting phenotypic expression.

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    Phenotypic Plasticity

    The ability of an organism to change its phenotype in response to environmental conditions, measured by reaction norms.

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    Reaction Norm

    The range of phenotypic expressions of a single genotype across different environments.

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    Gel electrophoresis

    A technique used to separate DNA or proteins based on size and charge.

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    CCR5 gene

    A gene that encodes a receptor on helper T cells, crucial for immune response.

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    Homozygous dominant (+/+)

    Genotype where both alleles are dominant, can be infected by HIV-1.

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    Heterozygous (+/D32)

    Genotype with one dominant and one recessive allele; infection possible, but slower progression to AIDS.

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    Calculating allele frequency

    Method for determining how common a specific allele is in a population.

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    Polyploidy

    A condition in which an organism has more than two complete sets of chromosomes.

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    Triploid

    An organism with three sets of chromosomes, often resulting from the fusion of a diploid and haploid gamete.

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    Tetraploid

    An organism with four sets of chromosomes, typically formed by the fusion of diploid gametes.

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    Gene duplication

    A process where a segment of DNA is copied, leading to extra gene copies.

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    Kleptogenesis

    A reproductive mode where one species uses sperm from another species to activate eggs, then discards the sperm nucleus.

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    Fitness effects of mutations

    Mutations can be neutral, beneficial, or deleterious to organisms.

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    Pseudogenes

    Gene copies that have lost their function and no longer code for proteins.

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    Sickle cell anemia

    A genetic disorder caused by a mutation in the hemoglobin gene, resulting in sickle-shaped red blood cells.

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    Paralogous genes

    Genes that have duplicated within a species and may have different functions.

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    Loss-of-function mutations

    Mutations that deactivate a gene, resulting in the absence of the corresponding protein.

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    Orthologous genes

    Genes in different species that evolved from a common ancestor.

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    Haploid gamete

    A reproductive cell that contains one set of chromosomes (half the diploid number).

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    Retroposition

    The insertion of processed mRNA into the genome.

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    Inversions

    DNA segments that are flipped and reinserted, altering gene order.

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    Diploid gametes

    Germ cells that contain two sets of chromosomes, typically produced through meiosis.

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    Linkage disruption

    When genes that are normally inherited together are separated.

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    Mutations rates

    The frequency at which mutations occur in a given genome over time.

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    Drosophila inversion polymorphism

    The variability of chromosomal inversions in Drosophila, linked to environmental factors.

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    Hemoglobin subunits

    Different globin chains produced at various stages of development.

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    Gene-by-Environment Interaction

    Variation in plasticity among genotypes across different environments.

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    Mutation

    A change in DNA sequence that generates new alleles, crucial for evolution.

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    DNA Composition

    DNA consists of deoxyribose sugar, phosphate group, and four nitrogenous bases.

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    Point Mutation

    A change in a single nucleotide in the DNA sequence.

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    Transitions vs. Transversions

    Transitions: purine to purine, or pyrimidine to pyrimidine. Transversions: purine to pyrimidine or vice versa.

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    Synonymous Mutation

    A mutation that does not change the amino acid sequence of a protein.

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    Nonsynonymous Mutation

    A mutation that alters the amino acid sequence of a protein.

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    Frameshift Mutation

    Mutations where nucleotides are added or deleted, altering the reading frame.

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    Nonsense Mutation

    A point mutation that creates a premature stop codon in the protein sequence.

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    Study Notes

    Variation Among Individuals

    • Chapter 5 focuses on mutation and variation.
    • Variation stems from three sources: genetic factors, environmental factors, and genotype-by-environment interactions.

    Genetic Variation

    • Phenylthiocarbamide (PTC) taste perception is linked to the TAS2R38 gene on chromosome 7.
    • Two alleles, PAV and AVI, influence PTC taste sensitivity.
    • PAV allele association with the ability to detect toxins.
    • Charts display the percentage of subjects with different PTC genotypes (PAV/PAV, AVI/PAV, AVI/AVI) and their corresponding taste intensity.

    Environmental Variation

    • Environmental variation includes traits not genetically controlled; these traits are not heritable.
    • Phenotypic plasticity: adaptability, including inducible defenses (e.g., in Daphnia).
    • Hesse et al. (2012) research explores how organisms deal with multiple threats.

    Genotype-by-Environment Interaction

    • Aversion to cilantro is linked to multiple genes.
    • Only a small percentage increase in cilantro aversion is tied to multiple copies of specific genes.
    • Therefore, cilantro aversion is partially genetic but also potentially influenced by environment and genotype-environment interactions.
    • An individual's response to various environments can be genetically controlled.
    • Genotype-environment interactions mean the phenotype may vary depending on the environment.
    • Reaction norm: A single genotype's expression across different environments.

    Mutation

    • The raw material for evolution is mutation.

    • Without mutation, there are no new alleles, genes, or evolution.

    • Studying mutations helps understand their role in evolution.

    • DNA is made up of deoxyribose sugar, a phosphate group, and nitrogenous bases.

    • The four bases are purines (adenine, guanine) and pyrimidines (thymine, cytosine).

    • DNA replicates with the aid of DNA polymerase through complementary base pairing.

    • Sometimes wrong bases pair, which aren't always corrected, resulting in point mutations.

    • This process involves the unwinding of the DNA helix and the synthesis of new strands of DNA.

    • DNA mutations in coding regions (exons) can be synonymous or nonsynonymous.

    • Synonymous mutations don't change the amino acid sequence; they are also known as silent mutations.

    • Nonsynonymous mutations cause changes in the amino acid sequence.

    • Frameshift mutations occur when nucleotides are added or deleted, altering the reading frame.

    • Nonsense mutations are caused by point mutations leading to stop codons.

    • Various types of point mutations, like insertions and deletions, directly affect amino acid sequences.

    Where New Genes Come From

    • Gene duplication, often from unequal crossing over in meiosis, is a source of new genes.
    • The extra gene copy can accumulate mutations without being immediately selected against.
    • The globin gene family exemplifies this; the family includes a-like and B-like gene clusters, evolving to produce different chain forms during embryonic, fetal, and adult stages.
    • Retroposition is another mechanism where processed mRNA is re-inserted into the genome.
    • Chondrodysplasia in dogs illustrates retroposition and its effects.

    Chromosomal Alterations

    • Inversions: DNA segments are cleaved, reversed, and re-annealed.
    • This can disrupt gene linkages and lead to dysfunctional gametes.
    • Chromosomal inversions, a characteristic of Drosophil, are also found in several populations and are tied to temperature and body size.
    • Polyploidy: Organisms may have extra sets of chromosomes, resulting in tetraploids, octoploids, hexaploids, and triploids.
    • Polyploidy commonly arises in plants and sometimes appears in hermaphroditic animals that self-fertilize.
    • Meiosis error can lead to diploid gametes.
    • In species where diploid gametes fuse with other diploid gametes, polyploidy can lead to offspring.

    Mutation Rate

    • Data for mutation rates are predominantly from loss-of-function mutations.
    • Loss-of-function mutations occur when a gene is inactivated, thus preventing the production of the associated protein.
    • A loss-of-function mutation typically doesn't lead to evolution quickly but is typically studied to determine the rate of mutation.
    • The mutation rates of genes vary across species and within species.
    • Factors like DNA polymerase error rate, mismatch repair system efficiency, and environmental conditions influence the rates.

    Measuring Genetic Variation

    • Historically, genetic variation was perceived as low within populations, but current techniques have revealed incredibly high levels.
    • Advancements in measuring genetic diversity rely on methods for directly measuring genomic and genetic variation.
    • Determining genotypes: Phenotypes are used to determine some genotypes (e.g., achondroplasia). Protein and DNA sequences are required to identify other genotypes.

    Calculating Allele Frequencies

    • Estimating the frequency of alleles involves examining genotypes. Example data (Ashkenazi populations) demonstrates different alleles and their variation.
    • The frequencies of alleles add up to one; this provides a useful check in calculating allele frequencies.

    How Much Genetic Diversity Is Typical

    • For the vast majority of organisms, between 15% and 33% of enzyme loci are polymorphic.
    • Average individuals are typically heterozygous for 4% to 15% of loci; this is an average across different taxa.
    • Heterozygosity, or mean heterozygosity, represents the average frequency of heterozygotes (individuals with two different alleles) based across loci and considers the fraction of loci in a population that have multiple alleles.
    • Charts display heterozygosity frequency distributions for Vertebrates, Plants and Invertebrates across various species' genetic diversity.

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    Mutation and Variation Among Individuals PDF

    Description

    This quiz covers Chapter 5's key concepts of variation among individuals, focusing on genetic variation, environmental influences, and genotype-by-environment interactions. Explore how mutations and different factors contribute to the diversity observed in traits, including taste sensitivity and phenotypic plasticity.

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