Biology Chapter 4: Mendelian Variations
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Questions and Answers

What is the main characteristic of codominance?

  • One allele suppresses the other
  • Both alleles are visible and distinct in the phenotype (correct)
  • Traits blend into an intermediate phenotype
  • Only one allele is expressed
  • In codominance, one allele may be recessive and suppressed by another allele.

    False

    What phenotype is produced in individuals with the genotype IAIB?

    Blood type AB

    In sickle-cell anemia, the genotype ____ results in the production of both normal and mutated hemoglobin.

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

    Match the following blood type genotypes with their corresponding phenotypes:

    <p>IAIA = Blood type A IBIB = Blood type B IAIB = Blood type AB ii = Blood type O</p> Signup and view all the answers

    Which of the following statements about the expression level in codominance is true?

    <p>Proteins produced by each allele function independently</p> Signup and view all the answers

    In codominance, the phenotypic ratio is typically 1:2:1.

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

    What occurs at the chromosomal level in codominance?

    <p>Both alleles remain active and contribute equally to the phenotype.</p> Signup and view all the answers

    What color feathers do the heterozygous offspring of black and white-feathered chickens exhibit?

    <p>Blue-gray</p> Signup and view all the answers

    In incomplete dominance, one allele fully dominates the other.

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

    What is the genotype of a gray-furred rabbit resulting from a cross between a black-furred rabbit and a white-furred rabbit?

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

    The color of feathers in F1 generation heterozygous chickens results from the ______ of black and white pigments.

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

    Which of the following explains why the blue-gray feathers are not a pure gray?

    <p>They result from the partial expression of black pigment.</p> Signup and view all the answers

    Name an example of a trait that is inherited through codominance.

    <p>ABO blood group system</p> Signup and view all the answers

    Match the following traits with their inheritance types:

    <p>Blue-gray chicken feathers = Incomplete dominance AB blood type = Codominance Gray rabbit fur = Incomplete dominance Spotted cattle coat = Codominance</p> Signup and view all the answers

    In incomplete dominance, the resulting phenotype is an intermediate form between two ______.

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

    What happens to red blood cells in individuals with the HbAHbS genotype during low oxygen conditions?

    <p>They become rigid and sickle-shaped.</p> Signup and view all the answers

    Individuals with HbAHbS usually experience severe symptoms.

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

    What term describes the condition where both normal and sickle-shaped red blood cells are present?

    <p>sickle cell trait</p> Signup and view all the answers

    A homozygous condition of a lethal gene must inherit two copies of the allele for it to be _____

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

    Match the type of lethal gene with its description:

    <p>Recessive Lethal Genes = Cause death when two copies are inherited Embryonic Lethality = Causes death before birth Late-Onset Lethal Genes = Lead to death later in life Yellow Coat Color in Mice = Controlled by a recessive lethal gene</p> Signup and view all the answers

    When a person with sickle cell trait has a child with someone who has normal hemoglobin, what is one possible genotype of their offspring?

    <p>Both A and C</p> Signup and view all the answers

    Lethal genes can only cause death during embryonic development.

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

    Define lethal genes in the context of genetics.

    <p>Alleles that cause the death of an organism when present in a particular combination.</p> Signup and view all the answers

    How many alleles can an individual organism inherit for a given gene?

    <p>Two alleles</p> Signup and view all the answers

    The ABO blood group system is an example of a trait controlled by multiple alleles.

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

    What is meant by 'hierarchy of dominance' in the context of multiple alleles?

    <p>It refers to the relationships among alleles where some alleles are completely dominant, partially dominant, or recessive to others.</p> Signup and view all the answers

    In the ABO blood group system, the alleles IA and IB are considered to be ____ to each other.

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

    Match the following alleles with their corresponding blood types:

    <p>IA = Blood type A IB = Blood type B i = Blood type O IAIB = Blood type AB</p> Signup and view all the answers

    Which of the following statements is true regarding phenotypic variety and multiple alleles?

    <p>Multiple alleles allow for more phenotypic variety</p> Signup and view all the answers

    With multiple alleles, an organism can express all alleles present in the population.

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

    What are the three alleles that determine an individual's blood type in the ABO blood group system?

    <p>IA, IB, and i</p> Signup and view all the answers

    What is the observed phenotypic ratio in the offspring of two heterozygous yellow-coated mice (Yy)?

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

    A homozygous lethal individual (yy) will survive to adulthood.

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

    Name a prominent example of a dominant lethal gene.

    <p>Huntington's disease</p> Signup and view all the answers

    The lethal allele in the case of two heterozygous yellow-coated mice results in death during the _____ stage.

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

    What happens to individuals with a dominant lethal allele?

    <p>They typically die before reproductive age.</p> Signup and view all the answers

    Individuals with one copy of the mutated allele of Huntington's disease remain symptom-free until later in life.

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

    What is the genotypic outcome ratio expected from two heterozygous yellow-coated mice?

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

    Match the type of lethal genes with their characteristics:

    <p>Dominant Lethal Genes = Fatal even in one copy, often leading to early death Huntington's Disease = Fatal in adulthood but allows for reproduction Homozygous Recessive Lethal Genes = Causes death in the embryonic stage if present in two copies Lethal Alleles = Genes that can cause the death of the organism</p> Signup and view all the answers

    What is an example of a dominant lethal gene in chickens?

    <p>Creeper allele</p> Signup and view all the answers

    Homozygous Manx cats can survive without any issues.

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

    What phenotype do heterozygous individuals (Aa) with achondroplasia exhibit?

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

    In Chickens, the _______ allele is lethal when homozygous.

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

    Match the following animals with their corresponding lethal gene characteristics:

    <p>Creeper Chickens = Heterozygous exhibit short-legged phenotype Manx Cats = Taillessness due to dominant lethal gene Achondroplasia = Dwarfism caused by a dominant allele Siamese Cats = Not a lethal gene, normal survival</p> Signup and view all the answers

    Multiple alleles refer to more than two forms of a gene in a population.

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

    The gene responsible for taillessness in Manx cats is a _______ lethal gene.

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

    Study Notes

    Chapter 4: Variations of Mendelian Inheritance

    • This chapter discusses variations on Mendelian inheritance principles, going beyond simple dominant/recessive patterns.

    Mendelian Inheritance?

    • Questions the fundamental concepts of Mendelian inheritance.

    Variations of Mendelian Inheritance

    • Incomplete Dominance
    • Codominance
    • Lethal Genes
    • Multiple Alleles
    • Polygenes
    • Epistasis

    Gene Interaction

    • Gene interactions describe various ways two or more genes influence each other impacting the phenotype.
    • Allelic or Non-epistatic
    • Non-allelic or Epistatic

    Incomplete Dominance

    • Definition: A form of inheritance where the heterozygote's phenotype is an intermediate blend of both homozygous parents.
    • Deviation from Mendelian Dominance: Unlike Mendel's concept of complete dominance, where one allele masks the other, incomplete dominance blends parental traits.
    • Phenotype Result: A distinct intermediate phenotype is produced (neither dominant nor recessive). Example 1:2:1 ratio

    Mechanism of Incomplete Dominance

    • Dosage Effect: The heterozygote produces less of the gene product (usually a protein) compared to the homozygote for the dominant allele.
    • Gene Expression: Both alleles contribute to the phenotype, but the gene products are insufficient to fully express either trait alone.

    Example: Flower Color in Snapdragon

    • Parental Generation: Red-flowered plant (CRCR) and White-flowered plant (CWCW)
    • F1 Generation: All offspring are heterozygous (CRCW) and display a pink phenotype (intermediate phenotype)
    • Reason for Pink Color: The red allele (CR) only partially contributes to flower color, and the white allele (CW) also contributes but not fully, resulting in a blend or an intermediate trait between red and white-pink.

    Example: Andalusian Chicken Feather Color

    • Parental Generation: Black-feathered chicken (CBCB) and White-feathered chicken (CWCW)
    • F1 Generation: All offspring are heterozygous (CBCW) and display a blue-gray phenotype
    • Reason for Blue-Gray Color: The black allele (CB) doesn't entirely dominate the white allele(CW), but instead, the black pigment is diluted, resulting in a "softer," blue-gray color.

    Why Blue, Not Gray?

    • Blue-gray is not simply an average of black and white. The color arises from the partial expression of black pigment.
    • When diluted, it creates a bluish tone due to how light interacts with the diluted pigment, creating a more distinct blue-gray color (instead of pure gray, which is a mix of black and white)

    Sample Problem: Incomplete Dominance (Rabbits)

    • In a certain breed of rabbits, the allele for black fur (B) is incompletely dominant to the allele for white fur (W).
    • A gray-furred rabbit (BW) is crossed with a white-furred rabbit (WW).
    • Expected genotypes and phenotypes of 16 offspring (problem-solving example).

    Codominance

    • Definition: A form of inheritance where both alleles in a heterozygous organism are fully and equally expressed, simultaneously displaying both traits.
    • Phenotypic Result: Traits from both alleles are visible. Example ratio: 1:2:1

    Mechanism of Codominance

    • Chromosomal Level: Both alleles at a specific locus on homologous chromosomes remain active and equally contribute to the phenotype.
    • Expression Level: Both alleles independently code for proteins, co-expressed; proteins function independently but are observable in the phenotype.

    Example: Codominance of Blood Types A and B

    • Alleles: IA codes for the A antigen, IB codes for the B antigen, i codes for neither antigen (O)
    • Genotype: IAIB (Blood type AB) - both A and B antigens are displayed equally on red blood cells.

    Example: Codominance in Sickle-Cell Anemia

    • Alleles: HbA (normal hemoglobin), HbS (mutated, sickle-shaped hemoglobin)
    • Genotype: HbAHbS (Heterozygous)
    • Phenotype: Both normal and sickle-shaped hemoglobin proteins are produced.
    • Health Effects: Heterozygous individuals usually have mild symptoms, but they may experience mild sickling under low oxygen conditions.

    Sample Problem: Codominance

    • In humans, the allele for normal hemoglobin (HbA) and the allele for sickle-cell hemoglobin are codominant.
    • Problem-solving exercise (creating a Punnett square to predict offspring genotypes and phenotypes).

    Lethal Genes

    • Definition: Lethal genes cause an organism's death when present in a particular combination.
    • Types: Recessive and Dominant Lethal Genes

    Recessive Lethal Genes

    • Definition: An individual must inherit two copies of the lethal allele to be fatal. Example: In mice, the yellow coat color is controlled by a lethal gene.

    Dominant Lethal Genes

    • A dominant lethal allele is fatal when present in a single copy.
    • Example: Huntington's Disease
    • Example: Creeper Chickens
    • Example: Manx Cats

    Sample Problem: Lethal Genes

    • Achondroplasia: A form of dwarfism; dominant allele (A), but homozygous genotype is lethal before birth.

    Multiple Alleles

    • Definition: More than two alternative forms of a gene (alleles) exist for a particular trait in a population (leading to greater genetic variation).
    • Organisms only carry two alleles, but there are over two gene variants.
    • Example: ABO Blood Group System in Humans (IA, IB, i)
    • Example: Coat Color in Rabbits (C, cch, ch, c)

    Sample Problems (Multiple Alleles)

    • Problems related to specific genetic inheritance patterns involving multiple alleles for traits like coat color in rabbits.

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    Description

    Explore the variations of Mendelian inheritance in this quiz, including concepts like incomplete dominance, codominance, and lethal genes. Understand how gene interactions impact phenotypes beyond simple dominant and recessive models. Test your knowledge of these complex genetic principles.

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