Incomplete Dominance and Overdominance Biology
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Questions and Answers

What is true about blood type O in relation to blood types A and B?

  • Blood type O is expressed when both A and B genes are present.
  • Blood type O is a result of co-dominance.
  • Blood type O is dominant over A and B.
  • Blood type O does not get expressed if A and B genes are expressed. (correct)

    • Which of the following describes co-dominance?

  • The offspring display a mix of both parental traits.
  • Both traits are expressed independently in the offspring. (correct)
  • One trait is dominant over the other in the offspring.
  • Only one trait from the parents is expressed in the offspring.

    • What distinguishes sex-influenced traits from sex-limited traits?

  • Sex-influenced traits appear only in one sex.
  • Sex-limited traits are influenced by environmental factors.
  • Sex-influenced traits are always sex-linked.
  • Sex-influenced traits vary based on the sex of the individual. (correct)

    • Which of the following is an example of a sex-influenced trait?

    <p>Scurs in cattle.</p> Signup and view all the answers

    How does scurs express differently in males compared to females?

    <p>Scurs are dominant in males but recessive in females.</p> Signup and view all the answers

    Which allele combination results in type O blood?

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

    What genetic phenomenon is demonstrated when both A and B proteins are present in type AB blood?

    <p>Co-dominance</p> Signup and view all the answers

    What type of enzyme does the i allele encode?

    <p>An inactive enzyme</p> Signup and view all the answers

    Which of the following accurately describes the inheritance pattern of ABO blood types?

    <p>Different from a typical dominance/recessive relationship</p> Signup and view all the answers

    What sugar is added to the carbohydrate tree to produce the A antigen?

    <p>N-acetyl-galactosamine</p> Signup and view all the answers

    Which of the following combinations represents a person with type B blood?

    <p>I B I B</p> Signup and view all the answers

    Which blood type can arise from the genetics of co-dominance?

    <p>AB only</p> Signup and view all the answers

    How many alleles are involved in determining a person's ABO blood type?

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

    What phenotype do CRCW flowers exhibit in terms of color?

    <p>Pink color</p> Signup and view all the answers

    What is the expected phenotypic ratio in the F2 generation for traits exhibiting incomplete dominance?

    <p>1:2:1</p> Signup and view all the answers

    Which of the following traits in humans is an example of incomplete dominance?

    <p>Wavy hair</p> Signup and view all the answers

    How does incomplete dominance differ from complete dominance?

    <p>Incomplete dominance results in a mix of phenotypes.</p> Signup and view all the answers

    In the pea plant example, what does a microscopic examination reveal about the genotypes?

    <p>R and r show incomplete dominance in starch biosynthesis.</p> Signup and view all the answers

    What is the dominant trait in humans regarding hair texture?

    <p>Curly hair</p> Signup and view all the answers

    What alleles correspond to red and white flower colors in the four-o'clock plant?

    <p>CR and CW</p> Signup and view all the answers

    What does the term 'overdominance' refer to in genetics?

    <p>When heterozygotes show greater fitness than either homozygote.</p> Signup and view all the answers

    What characteristic defines simple Mendelian inheritance?

    <p>Strict dominant/recessive relationship</p> Signup and view all the answers

    How do males and females differ in X-linked inheritance?

    <p>Males have a single copy of X-linked genes.</p> Signup and view all the answers

    What does incomplete penetrance indicate about a dominant allele?

    <p>The presence of the dominant allele does not guarantee expression.</p> Signup and view all the answers

    Which scenario describes incomplete dominance?

    <p>A cross yields offspring with a mixed phenotype.</p> Signup and view all the answers

    What is the molecular basis for the dominant trait in simple Mendelian inheritance?

    <p>50% of functional protein is sufficient.</p> Signup and view all the answers

    Which of the following best describes incomplete penetrance?

    <p>Expression of the dominant allele is inconsistent among individuals.</p> Signup and view all the answers

    What does overdominance in inheritance refer to?

    <p>Heterozygotes have a reproductive advantage over both homozygotes.</p> Signup and view all the answers

    In inheritance patterns, which option represents X-linked traits?

    <p>Trait can be expressed in males even with a single allele.</p> Signup and view all the answers

    In codominance, which statement is true?

    <p>Both alleles are expressed simultaneously.</p> Signup and view all the answers

    In incomplete dominance, how does the phenotype of heterozygotes compare to homozygotes?

    <p>Heterozygotes display a phenotype intermediating the two homozygotes.</p> Signup and view all the answers

    What characterizes sex-influenced inheritance?

    <p>Some alleles are recessive in one sex and dominant in the other.</p> Signup and view all the answers

    Which statement describes sex-limited inheritance accurately?

    <p>Sex hormones determine whether a trait is expressed in one sex only.</p> Signup and view all the answers

    What does a lethal allele typically cause?

    <p>Potential death of an organism.</p> Signup and view all the answers

    How can heterozygotes gain benefits through overdominance?

    <p>They may have increased resistance to infections.</p> Signup and view all the answers

    What is NOT true about codominance?

    <p>The resulting phenotype is a mix of both alleles.</p> Signup and view all the answers

    Which feature is common among lethal alleles?

    <p>They encode non-functional proteins necessary for survival.</p> Signup and view all the answers

    What type of genetic trait is typically expressed only in one sex and contributes to sexual dimorphism?

    <p>Sex-limited traits</p> Signup and view all the answers

    Which of the following statements about lethal alleles is correct?

    <p>Lethal alleles are generally inherited in a recessive manner.</p> Signup and view all the answers

    What is an example of a condition that results from a conditional lethal allele?

    <p>Temperature-sensitive lethals in Drosophila</p> Signup and view all the answers

    Which of the following statements best describes pleiotropy?

    <p>Multiple effects of a single gene on various phenotypes.</p> Signup and view all the answers

    What is the consequence of having a homozygous dominant genotype for a lethal allele?

    <p>Genotype is not viable and offspring is absent.</p> Signup and view all the answers

    How do semilethal alleles differ from lethal alleles?

    <p>Semilethal alleles affect only some individuals, not all.</p> Signup and view all the answers

    What role does the MITF gene play in coat color patterns for certain animals?

    <p>It encodes an essential protein for pigmentation migration and survival.</p> Signup and view all the answers

    Which example illustrates epistasis?

    <p>A gene that prevents the expression of another gene's phenotype.</p> Signup and view all the answers

    What is a characteristic of nonessential genes?

    <p>They can still provide benefits to the organism.</p> Signup and view all the answers

    What effect do lethal alleles generally have on Mendelian ratios?

    <p>They may alter expected ratios by eliminating certain genotypes.</p> Signup and view all the answers

    At what stage of life may some lethal alleles manifest their effects?

    <p>In early adulthood or later in life.</p> Signup and view all the answers

    What is an effect of environmental conditions on conditional lethal alleles?

    <p>They affect a developing organism only in specific circumstances.</p> Signup and view all the answers

    Which of the following traits is an example of sexual dimorphism?

    <p>Plumage differences between male and female birds.</p> Signup and view all the answers

    What genetic phenomenon is illustrated by cystic fibrosis?

    <p>Pleiotropy due to a single gene affecting multiple functions.</p> Signup and view all the answers

    Study Notes

    Incomplete Dominance

    • Heterozygotes exhibit an intermediate phenotype between the two homozygotes

    • Example: Flower color in four o'clock plants

      • Two alleles: CR (red) and CW (white)
      • CRCR = red flowers
      • CWCW = white flowers
      • CRCW = pink flowers

    • F₂ generation ratio is 1:2:1 (not 3:1 like in simple Mendelian inheritance)

    • Pea shape example:

      • RR and Rr = round peas
      • rr = wrinkled peas
      • Microscopic examination shows incomplete dominance in starch biosynthesis

    Wavy Hair in Humans

    • Curly hair is dominant, straight hair is recessive
    • Heterozygous individuals have wavy hair (intermediate phenotype)
    • Incomplete dominance results in a novel phenotype (not curly or straight)
    • Genotypic ratio of offspring from homozygous parents is 1:2:1 (e.g., curly:wavy:straight)

    Overdominance

    • Heterozygote has greater reproductive success than either homozygote

    • Also called heterozygote advantage

    • Heterozygote Aa superior to either homozygote AA or aa

    • Example: Sickle-cell anemia

      • Autosomal recessive disorder
      • Affected individuals produce abnormal hemoglobin (HbS)
      • Normal hemoglobin (HbA)
      • Two major ramifications of HbS HbS:
        • Shortened red blood cell lifespan (anemia)
        • Clumping of red blood cells, blocking capillary circulation.
      • Affected individuals have shorter life spans than unaffected ones
      • Heterozygotes (HbA HbS) display resistance to malaria

    • Phenotype falls outside range of parents:

      • e.g., one homozygote is tall (TT), the other is short (tt)
      • Heterozygote (Tt) can be extra tall
      • If this adaptation is good, it might become common in the population

    Codominance

    • Both alleles in a heterozygote are fully expressed.
    • No dominant/recessive relationship
    • Example: ABO blood types
      • Three alleles: IA, IB, and i
        • i is recessive to IA and IB
        • ii = type O blood
        • IAIA or IAi = type A blood
        • IBIB or IBi = type B blood
        • IAIB = type AB blood
    • Alleles IA and IB are codominant

    Livestock Examples

    • Co-dominance occurs in different animals, influencing skin and feather colors.
    • Example: Breeding of white and black chickens leads to offspring with both white and black feathers.
    • Example: Breeding of black and white cows generates spotted cows

    Sex-Influenced Traits

    • An allele is dominant in one sex but recessive in the other.
    • Not sex-linked
    • Example: Scurs in cattle
      • Dominant in males, recessive in females
      • Sc is dominant in males, Sc^ is dominant in females
    • Autosomal

    Sex-Limited Traits

    • Traits that occur in only one sex.
    • Generally autosomal (not sex-linked)
    • Examples:
      • Human sexual dimorphism (Ovaries in females, testes in males)
      • Bird plumage/features (e.g., roosters have more elaborate plumage than hens)

    Lethal Alleles

    • Alleles that cause death of an organism.
    • Typically result from mutations in essential genes
    • Usually inherited in a recessive manner
      • Example: Huntington's disease (progressive nervous system degeneration and dementia, with early death).
      • Example: Temperature-sensitive alleles kill an organism only under specific environmental conditions, like in a developing Drosophila larva.
      • Example: Manx cat: Short tail is a dominant trait, but lethal in homozygous form
    • Some lethal alleles affect the organism later in life.

    Gene Interactions

    • Two or more genes affect a single trait
    • Morphological characteristics (e.g., height, weight, pigmentation) are affected by many genes in combination with environmental factors.

    Epistasis

    • One gene masks the effect of another gene.
    • Example: Flower color in sweet peas
      • Two genes (C and P) affect flower color
      • Recessive alleles (cc) or (pp) can mask the effects of the dominant traits and result in white flowers
      • Two genes needed to produce purple pigment

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    Introduction to Genetics PDF

    Description

    This quiz covers the principles of incomplete dominance and overdominance in genetics. You'll explore how heterozygotes exhibit intermediate phenotypes, as seen in flower color and human hair texture. Additionally, discover the advantages of heterozygotes in natural selection. Test your understanding of these genetic concepts!

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