Quantitative Genetics (T 211) - Lecture 6
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Questions and Answers

What is the relationship between an individual's breeding value and its expected progeny performance?

  • Breeding value is unrelated to progeny performance
  • Breeding value is half of progeny performance
  • Breeding value is twice the progeny performance (correct)
  • Breeding value equals progeny performance

    • Transmitting ability refers to the complete genetic contribution of an individual to its offspring.

    False

    What is the formula for the breeding value of the genotype 𝐴1𝐴2?

    (q – p) α = α1 + α2

    The expected progeny performance is also known as ______.

    <p>transmitting ability</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Breeding Value = Twice the deviation of progeny from population mean Transmitting Ability = Half of the breeding value Genotype A1A1 = 2 q α = 2 α1 Genotype A2A2 = −2 p α = 2 α2</p> Signup and view all the answers

    When mating is random, how is the breeding value defined?

    <p>Sum of the average effects of the two alleles</p> Signup and view all the answers

    Inbreeding increases genetic diversity within a population.

    <p>False</p> Signup and view all the answers

    The breeding value of an individual is defined as twice the ______ of its progeny from the population mean.

    <p>deviation</p> Signup and view all the answers

    Which of the following statements is true regarding genetic transmission?

    <p>Only additive genetic effects can be passed on to progeny.</p> Signup and view all the answers

    A heterozygote organism can transmit both alleles to its progeny.

    <p>False</p> Signup and view all the answers

    What is the genotypic value?

    <p>The phenotype exhibited by a given genotype averaged across environments.</p> Signup and view all the answers

    The __________ is the portion of the genotypic value that determines the performance of the offspring.

    <p>breeding value</p> Signup and view all the answers

    Match the following genetic concepts with their definitions:

    <p>Genotypic Value = The phenotype of a genotype averaged across environments Breeding Value = The part of genotypic value affecting offspring performance Additive Genetic Effects = Genetic effects that can be inherited by progeny Non-additive Genetic Effects = Genetic effects that cannot be passed on to offspring</p> Signup and view all the answers

    Which of the following is NOT a symptom of inbreeding depression in plants?

    <p>Increased pollen production</p> Signup and view all the answers

    Inbreeding refers to the mating of individuals with a degree of relationship that is:

    <p>Higher than the average relationship within the population</p> Signup and view all the answers

    What is the primary outcome of inbreeding in terms of genetic variation?

    <p>Reduced genetic diversity</p> Signup and view all the answers

    What is the main difference in effect between heterosis and inbreeding?

    <p>Heterosis increases performance while inbreeding decreases performance</p> Signup and view all the answers

    What is the relationship between inbreeding and homozygosity?

    <p>Inbreeding increases homozygosity</p> Signup and view all the answers

    Which of the following is NOT a consequence of inbreeding depression?

    <p>Enhanced fertility</p> Signup and view all the answers

    Which of these is a characteristic of outbreeding?

    <p>Mating of individuals with a lower degree of relationship</p> Signup and view all the answers

    Which statement BEST describes the effect of inbreeding on recessive disease inheritance?

    <p>Inbreeding increases the chance of inheriting recessive diseases</p> Signup and view all the answers

    What components make up phenotype (P)?

    <p>Genotype, environment, and genotype-environment interaction</p> Signup and view all the answers

    Breeding value (BV) is solely based on an individual's environmental factors.

    <p>False</p> Signup and view all the answers

    What is the formula for calculating genetic value?

    <p>G = A + D</p> Signup and view all the answers

    The sum of all genetic effects of genes is known as the __________.

    <p>genotype</p> Signup and view all the answers

    Which of the following statements best describes breeding value?

    <p>It is the sum of average effects of genes transmitted to offspring.</p> Signup and view all the answers

    Genetic value is transmitted to progeny in its entirety.

    <p>False</p> Signup and view all the answers

    Define 'average effect' in the context of genetics.

    <p>The average effect of gene substitution is the mean change due to changing A2 genes chosen at random into A1 genes.</p> Signup and view all the answers

    Which of the following statements is NOT true about inbreeding?

    <p>Inbreeding can result in the elimination of deleterious recessive alleles.</p> Signup and view all the answers

    Which of the following statements is true regarding overdominance?

    <p>The heterozygous genotype exhibits a phenotype that is superior to both homozygous genotypes.</p> Signup and view all the answers

    Which of the following is a characteristic of outbreeding?

    <p>Individuals are heterozygous at many loci.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of species that exhibit severe inbreeding depression?

    <p>They are self-pollinated.</p> Signup and view all the answers

    Inbreeding refers to:

    <p>The process of mating individuals that are more closely related than random individuals from the population.</p> Signup and view all the answers

    Which of the following statements is CORRECT regarding the fitness of individuals?

    <p>Fitness refers to the ability of an individual to survive and reproduce in a given environment.</p> Signup and view all the answers

    What is a primary consequence of inbreeding?

    <p>Increased likelihood of homozygous individuals.</p> Signup and view all the answers

    Which of the following is a key difference between outbreeding and inbreeding?

    <p>Outbreeding promotes heterozygosity, while inbreeding promotes homozygosity.</p> Signup and view all the answers

    What is inbreeding?

    <p>Mating of individuals who are related more than the average in the herd.</p> Signup and view all the answers

    Inbreeding always increases genetic diversity in a population.

    <p>False</p> Signup and view all the answers

    What is inbreeding depression?

    <p>Inbreeding depression is the reduced survival and fertility of offspring from related individuals.</p> Signup and view all the answers

    Inbreeding increases __________ and decreases __________.

    <p>homozygosity; heterozygosity</p> Signup and view all the answers

    Match the symptoms of inbreeding depression with their descriptions:

    <p>Reduced plant vigor = Lowered growth rates Smaller plant size = Decrease in overall size Decline in fertility = Reduced ability to produce offspring Greater susceptibility to damage = Higher risk from pests or diseases</p> Signup and view all the answers

    Which of the following is a symptom of inbreeding depression?

    <p>Decreased pollen production</p> Signup and view all the answers

    Heterosis, or hybrid vigor, improves performance compared to inbreeding.

    <p>True</p> Signup and view all the answers

    List one effect of inbreeding on offspring.

    <p>Reduced survival or fertility</p> Signup and view all the answers

    Which of the following is a reason for practicing inbreeding?

    <p>To create genetic uniformity</p> Signup and view all the answers

    The coefficient of inbreeding (F) is always between 0 and 1.

    <p>True</p> Signup and view all the answers

    What does the term 'inbreeding depression' refer to?

    <p>The decrease in fitness or performance that often accompanies inbreeding.</p> Signup and view all the answers

    The measure of relationship between mating pairs is denoted as the coefficient of ______.

    <p>inbreeding</p> Signup and view all the answers

    Match the following terms related to inbreeding with their definitions:

    <p>F = Coefficient of inbreeding Homozygosity = Presence of identical alleles at a locus Recessive alleles = Alleles that may express less favorably Inbreeding depression = Decrease in the fitness of individuals due to inbreeding</p> Signup and view all the answers

    If F equals 0, what does this indicate about a population?

    <p>The population experiences random mating</p> Signup and view all the answers

    What is meant by 'increasing homozygosity' in the context of inbreeding?

    <p>It refers to the process of bringing together identical alleles at a locus through inbreeding.</p> Signup and view all the answers

    Inbreeding is always beneficial for a population's overall fitness.

    <p>False</p> Signup and view all the answers

    What is the primary factor that determines an offspring's breeding value?

    <p>The random sample of genes inherited from its parents</p> Signup and view all the answers

    Which statement correctly describes the relationship between parental breeding values and offspring?

    <p>The average breeding value of the parents does not guarantee offspring will inherit it</p> Signup and view all the answers

    What distinguishes genetic value from breeding value?

    <p>Genetic value cannot be passed on to progeny</p> Signup and view all the answers

    Why are expected progeny differences (EPDs) significant in animal breeding?

    <p>They allow for comparisons of individuals within the same breed</p> Signup and view all the answers

    What is the implication of an EPD indicating a high value for an individual?

    <p>It is not necessarily the most desirable animal</p> Signup and view all the answers

    How does dominance deviation contribute to breeding value?

    <p>It distinguishes between additive and non-additive effects</p> Signup and view all the answers

    Which factor is considered when estimating breeding values?

    <p>The additive gene effects of the parental genes</p> Signup and view all the answers

    In what scenario can the breeding value be considered more significant than genetic value?

    <p>When looking to predict performance traits in offspring</p> Signup and view all the answers

    What is the primary effect of inbreeding on the genetic composition of a population?

    <p>No change in allele frequency</p> Signup and view all the answers

    What is the main reason why heterosis often leads to superior F1 hybrids?

    <p>F1 hybrids display a higher frequency of dominant alleles, suppressing undesirable recessive traits.</p> Signup and view all the answers

    Which of these scenarios demonstrates the most extreme form of inbreeding?

    <p>Self-pollination</p> Signup and view all the answers

    What is the primary benefit of heterosis in agricultural practices?

    <p>Improved yield and performance of the offspring.</p> Signup and view all the answers

    What is a potential consequence of inbreeding in a population?

    <p>Increased susceptibility to deleterious recessive traits.</p> Signup and view all the answers

    What is the relationship between inbreeding and the frequency of deleterious recessive alleles?

    <p>Inbreeding has no effect on the frequency of deleterious recessive alleles.</p> Signup and view all the answers

    How can the potential negative effects of inbreeding be minimized in breeding programs?

    <p>By introducing new individuals from unrelated populations.</p> Signup and view all the answers

    What is the primary difference between heterosis and inbreeding?

    <p>Heterosis increases heterozygosity, while inbreeding increases homozygosity.</p> Signup and view all the answers

    What does the coefficient of inbreeding (F) measure in a population?

    <p>The probability that two genes at the same locus are identical by descent</p> Signup and view all the answers

    Inbreeding can lead to the expression of which type of alleles?

    <p>Recessive alleles that were previously hidden</p> Signup and view all the answers

    What is the range of the coefficient of inbreeding (F)?

    <p>0 to 1</p> Signup and view all the answers

    What is a potential outcome of inbreeding depression?

    <p>Reduced fitness due to a surge in lethal recessive traits</p> Signup and view all the answers

    Why might inbreeding be practiced in breeding research?

    <p>To create uniform genotypes for inbred cultivars</p> Signup and view all the answers

    What is indicated by an inbreeding coefficient (F) of 0?

    <p>There is no inbreeding occurring</p> Signup and view all the answers

    What is a consequence of increasing homozygosity in a population via inbreeding?

    <p>Increased chances of expressing harmful recessive alleles</p> Signup and view all the answers

    How does inbreeding generally affect the overall performance of individuals in a population?

    <p>It typically decreases performance due to inbreeding depression</p> Signup and view all the answers

    What is one advantage of inbreeding in genetic selection?

    <p>Identifies undesirable recessive genes</p> Signup and view all the answers

    Which of the following is a disadvantage of inbreeding?

    <p>Reduction in hybrid vigor</p> Signup and view all the answers

    In the case of full inbreeding, what is the value of F?

    <p>F = 1</p> Signup and view all the answers

    What effect does inbreeding have on homozygosity?

    <p>Increases homozygosity</p> Signup and view all the answers

    What is the formula for calculating the population mean in the case of partial inbreeding?

    <p>MF = a(p - q) + 2dpq(1 - F)</p> Signup and view all the answers

    Which of the following is an effect of increased homozygosity due to inbreeding?

    <p>Greater chance of lethal alleles</p> Signup and view all the answers

    What is a potential consequence of inbreeding on reproductive ability?

    <p>Decreased reproductive ability</p> Signup and view all the answers

    What does the term 'population mean' refer to in the context of random mating?

    <p>The average value of a trait in a population</p> Signup and view all the answers

    Which of the following outcomes does inbreeding NOT typically produce?

    <p>Increase in hybrid vigor</p> Signup and view all the answers

    In the context of inbreeding, which statement is true?

    <p>Inbreeding enhances the expression of recessive traits</p> Signup and view all the answers

    Study Notes

    Quantitative Genetics (T 211) - Lecture 6

    • Breeding values and population mean at inbreeding are discussed
    • Phenotype (P): observed and measured trait, determined by genotype, environment, and genotype-environment interaction
      • P = G + E + GE
    • Genotype (G): sum of all genetic effects of genes
    • Genotype vs Phenotype:
      • Genotype: organism's genetic information
      • Phenotype: observable physical traits
      • BB: homozygous dominant, purple
      • Bb: heterozygous, purple
      • bb: homozygous recessive, white
    • Genetic value
      • Breeding value + dominance deviation
      • Additive genetic effect (A) = breeding value
      • G = A + D
      • Value of an individual's genes to itself
      • Not transmitted to progeny
    • Average Effect
      • Average change due to gene substitution
    • Genotypic effects-one locus model
      • No dominance (d = 0)
      • Partial dominance (d < a)
      • Complete dominance (d = a)
      • Over dominance (d > a)
    • Breeding value (BV)
      • Value of an animal in a breeding program for a particular trait
      • Associated with genes carried by the individual and transmitted to offspring
      • Sum of average effects of genes
      • Value of an individual as a genetic parent
      • Part of genotypic value due to additive gene effects transmitted from parent to offspring
    • Breeding Value (BV)
      • Impossible to control/predict offspring's breeding value
      • Offspring's breeding value is the average of its parents' breeding values
    • Breeding value (BV)
      • Average of parental breeding values does not determine offspring's performance
      • Estimated breeding values (EBV) give an estimate of the average transmitting ability of a parent
      • Genetic value includes non-additive effects (dominance, etc) that aren't transmitted
    • Expected Breeding value (EPD)
      • Useful to compare/rank individuals within a breed, predict future offspring performance
      • Highest/lowest EPD not necessarily the most desirable; balanced EPDs are ideal
      • Only used to compare animals within the same breed
    • EBV (estimated breeding value)
      • Statistical method to predict genetic merit of an animal
      • Estimate of genetic potential for a quantitative trait
    • Quantitative Traits
      • Controlled by many genes and influenced by environment
      • Impossible to know actual genetic potential
      • Genetic potential estimated via statistical methods
      • Expressed relatively to the population mean; EBV has positive/negative symbol
    • Example: lamb A, EBV = +0.5kg, Mean= 3.5kg
      • Genetic potential of Lamb A = 4kg
      • Transmitting ability of Lamb A = 2kg
    • Example: lamb B, EBV = -0.5kg
      • Genetic potential of Lamb B = 3kg
      • Transmitting ability of Lamb B = 1.5kg
    • Breeding Value
      • Difference between genetic and breeding value largely dominance deviation
      • Individual can express dominance deviation (e.g. A₁A₂ heterozygote)
      • Individual cannot transmit dominance deviation, only one allele (e.g. A1A2 produces A₁ and A₂ gamete)
    • Genotypic and Breeding Values
      • Populations characterized by genetic variability
      • Genetic improvement based on selection of individuals differing in genotype
      • Variation in genotypic values represents the genotypic variance
    • Genotypic and Breeding Values
      • Genotypic value is the phenotype exhibited by a given genotype, averaged across environments.
      • Breeding value is the portion of genotypic value determining offspring performance
      • Only additive genetic effects are transmitted.
    • Breeding Value
      • Table showing different genotypes and associated breeding values (2q α₁; (q-p) α₁+ α₂ ; 2pα₂)
    • Breeding Value (BV)
      • An animal's breeding value is estimated to be twice the expected performance of its progeny.
      • The reason is only half the genes are transmitted to the offspring.
    • Transmitting ability is half the breeding value
    • Is the genetic advantage an individual transmits to its offspring
    • Breeding value of genotype is the sum of average effects of alleles
    • Useful concept: progeny phenotypic value is the mean of breeding values of two parents
    • Breeding values of an individual is twice the deviation of its progeny from the population average when mates are selected randomly.
    • Outbreeding: mating of individuals with a smaller degree of relationship than average
    • Inbreeding: mating of individuals with a greater than average degree of relationship
    • Inbreeding increases homozygosity, decreases heterozygosity, and increases chance of recessive disease inheritance
    • Inbreeding Depression
      • Reduced survival and fertility of offspring of related individuals
      • Occurrence varies between species
      • Average reduction in fitness or a character due to inbreeding
    • Symptoms of inbreeding depression
      • Reduced plant vigor, smaller plant size, decline in fertility, suppressed seed/pollen production, inferior seed quality, greater susceptibility to damage
    • Heterosis (Hybrid Vigor)
      • Superiority of F₁ hybrid over both parents in terms of yield or other traits
    • Benefits of heterosis
      • Increased yield, reproductive ability, size, quality, and adaptability
    • Estimate of heterosis = (F₁ - MP) / MP * 100
      • F₁ = Mean for the hybrid
    • MP = Mid parental value (P₁+P₂)/2
    • Important points about inbreeding
      • Inbreeding is a mating type that's important for plant breeders
      • Defined as mating of related individuals
      • Self-pollination is the most extreme inbreeding form
      • Inbreeding increases homozygosity, reduces heterozygosity
      • Allele frequencies remain stable while genotype frequencies change
    • Important points about inbreeding
    • Can occur unintentionally through natural selection or intentional maintenance of small populations
    • Deliberately used to create genetic uniformity in populations
    • Breeding research for retaining genotypes
    • Reliable production of inbred lines for hybrid cultivar development
    • Measurement of Inbreeding
      • Inbreeding coefficient (F): probability two genes are identical by descent.
      • F=0 for random mating
      • At the population level, F describes average homozygosity
      • F is always relative to the base population (F=0)
      • Ranges from 0 to 1
    • Increasing Inbreeding
      • Fitness (relative ability to survive/reproduce) declines with increased inbreeding in plants
      • Plant stature, vigor, yield, etc.
      • Strong differences between species (e.g., self-pollinated vs. polyploid) degree of inbreeding depression
    • Outbreeding vs Inbreeding: comparisons on mating mechanism, homozygosity, variability distribution, presence/absence of deleterious recessives, tolerance to inbreeding, heterozygote advantage/disadvantage
    • Inbreeding: closely related animals within a similar breed for 4-6 generations
      • Improves homozygosity, preserves race purity
      • Offspring are not superior to parents
      • Repeated inbreeding lowers productivity
    • Outbreeding: unrelated animals for 4–6 generations
      • Creates hybrids
      • Offspring superior to parents due to heterosis
      • Repeated outbreeding maintains superiority
    • Overdominance Hypothesis (The heterozygous progeny phenotypic value is greater than either parent)
    • Advantages of Inbreeding
      • Uniformity in families
      • Identification of undesirable recessive genes
      • Divergent lines for hybridization
    • Disadvantages of Inbreeding
      • Increase homozygosity
      • Lethal alleles
      • Reduced hybrid vigour
      • Decreased reproductive ability
      • Population segregation
      • Reduced yield
    • Population mean at inbreeding
      • Random mating (F=0): M₀ = a(p-q) + 2dpq
      • Partial inbreeding (0 < F < 1): M = a(p-q) + 2dpq(1-F)
      • Full inbreeding (F=1): M = a(p-q)

    References

    • List of URLs provided in the original document.

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    Lecture 6 Quantitative Genetics PDF

    Description

    This quiz covers key concepts from Lecture 6 of the Quantitative Genetics course, including breeding values, population mean at inbreeding, and the distinctions between genotype and phenotype. It delves into the genetic effects on traits and the methods of calculating genetic value, offering a comprehensive understanding of genetic interactions.

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