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

Which allele combination results in type O blood?

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

What type of enzyme does the i allele encode?

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

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

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

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

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

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

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

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

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

What phenotype do CRCW flowers exhibit in terms of color?

<p>Pink color (A)</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 (B)</p> Signup and view all the answers

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

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

How does incomplete dominance differ from complete dominance?

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

What is the dominant trait in humans regarding hair texture?

<p>Curly hair (B)</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 (A)</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. (B)</p> Signup and view all the answers

What characteristic defines simple Mendelian inheritance?

<p>Strict dominant/recessive relationship (C)</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. (D)</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. (C)</p> Signup and view all the answers

Which scenario describes incomplete dominance?

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

What does overdominance in inheritance refer to?

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

In codominance, which statement is true?

<p>Both alleles are expressed simultaneously. (A)</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. (B)</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. (C)</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. (D)</p> Signup and view all the answers

What does a lethal allele typically cause?

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

How can heterozygotes gain benefits through overdominance?

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

What is NOT true about codominance?

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

Which feature is common among lethal alleles?

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

How do semilethal alleles differ from lethal alleles?

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

Which example illustrates epistasis?

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

What is a characteristic of nonessential genes?

<p>They can still provide benefits to the organism. (D)</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. (A)</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. (B)</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. (D)</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. (A)</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. (C)</p> Signup and view all the answers

Flashcards

Incomplete Dominance

A heterozygote's phenotype is between the two homozygotes' phenotypes.

Four o'clock flower color

Example of incomplete dominance; heterozygotes are pink.

Incomplete Dominance in Pea Shape

Even dominant traits (like round peas) can have incomplete dominance at a microscopic level, like starch biosynthesis.

Wavy hair

An example of incomplete dominance in humans. An intermediate phenotype between curly and straight hair.

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Heterozygote

An organism with two different alleles for a trait.

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Homozygote

An organism with two identical alleles for a trait.

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Phenotype Ratio (F2)

In incomplete dominance, the phenotypic ratio in the F2 generation is 1:2:1 instead of 3:1 as seen in simple Mendelian inheritance.

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Alleles

Different versions of a gene responsible for a trait.

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Multiple Alleles

A gene with more than two possible alleles.

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ABO Blood Type

Blood type determined by three alleles (IA, IB, i).

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Codominance

Both alleles are expressed fully in the phenotype.

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Blood Type Alleles (IA, IB, i)

IA and IB are codominant, i is recessive.

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Type O Blood

Has the ii genotype.

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Type A Blood

Has IAIA or IAi genotype.

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Type B Blood

Has IBIB or IBi genotype.

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Type AB Blood

Has IAIb genotype (co-dominance).

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Sex-influenced Inheritance

A type of inheritance where the expression of a trait is influenced by the sex of the individual. An allele may be dominant in one sex but recessive in the other.

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Sex-limited Inheritance

A type of inheritance where the expression of a trait is limited to one sex. The gene for the trait may be present in both sexes, but it is only manifested in one.

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Scurs in Cattle

Small growths on the skull of cattle. This trait is an example of sex-influenced inheritance, being dominant in males and recessive in females.

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Are scurs dominant in females?

No, scurs are recessive in females. This means that a female cow must inherit two copies of the scurs allele to display the trait.

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What are sex-limited traits?

Traits expressed only in one sex, even if the genes are present in both. They contribute to sexual dimorphism.

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What are lethal alleles?

Alleles that cause death when present in homozygous state, often due to mutations in essential genes.

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Essential Genes

Genes required for survival, without their protein product, death occurs.

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Nonessential Genes

Genes that don't impact survival directly but still benefit the organism.

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Conditional Lethal Alleles

Alleles that become lethal only under specific environmental conditions, like temperature.

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Semilethal Alleles

Alleles that cause death in some individuals but not all.

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How do lethal alleles affect Mendelian ratios?

They can alter expected ratios because certain genotypes are not present, as they are lethal.

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Pleiotropy

A single gene affecting multiple traits.

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Why does pleiotropy occur?

The gene product might influence many cell functions, or the gene might be expressed in different cell types, or at different developmental stages.

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Cystic fibrosis

A disease caused by a mutated gene affecting chloride transport, leading to various debilitating effects.

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What determines coat color patterns in mammals?

Multiple alleles of a gene, like the spotting gene, regulate melanoblast migration and survival, creating white spotting.

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What is the spotting gene?

A gene that encodes MITF, a protein involved in melanoblast activity, affecting white spotting in coats.

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Gene interactions

Two or more genes influencing the outcome of a single trait.

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Epistasis

One gene's alleles masking the effects of another gene's alleles.

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Multiple gene interaction in traits

Several genes, along with environmental factors, contribute to complex traits like height and weight.

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Simple Mendelian Inheritance

Inheritance where alleles follow Mendel's laws and show a strict dominant/recessive pattern. The dominant allele produces a functional protein, and even half the amount is enough for the dominant trait.

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X-linked Inheritance

Inheritance pattern for genes located on the X chromosome. Males only have one X, while females have two, leading to different expression patterns.

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Incomplete Penetrance

A dominant allele is present, but the dominant trait is not always expressed. This can be due to environmental factors or other genes.

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What is the molecular explanation for Incomplete Dominance?

50% of a functional protein is not sufficient to produce the same trait as a homozygote with 100% of that protein.

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How is protein function related to Mendelian Inheritance?

A dominant allele often encodes a functional protein that is involved in the expression of a trait. In some cases, even half the amount of protein can be enough to produce the dominant phenotype.

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What is the difference between Incomplete Dominance and Simple Mendelian Inheritance?

In simple Mendelian inheritance, one allele is completely dominant over the other. In incomplete dominance, the heterozygote exhibits a phenotype that is intermediate between the two homozygous phenotypes.

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How does environment impact gene expression?

Environmental factors can influence whether or not a dominant trait is expressed, even when the dominant allele is present. This is known as incomplete penetrance.

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Overdominance

Heterozygotes have a trait that gives them greater reproductive success than either homozygote.

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Lethal Allele

An allele that can cause the death of an organism.

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What is a common reason for lethal alleles?

They are often loss-of-function alleles that encode proteins crucial for survival. Mutations can make these proteins non-functional.

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How can a mutation in a nonessential gene be lethal?

The mutation can cause the protein to function abnormally, leading to harmful consequences.

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Give an example of a lethal allele.

Many genetic diseases are caused by lethal alleles, leading to premature death or severe health problems.

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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

  • Fâ‚‚ 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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