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 (B)

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

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

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

In incomplete dominance, one allele fully dominates the other.

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

Individuals with HbAHbS usually experience severe symptoms.

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

Lethal genes can only cause death during embryonic development.

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

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

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

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

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

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

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

Homozygous Manx cats can survive without any issues.

<p>False (B)</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 (A)</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

Flashcards

Incomplete Dominance

A type of inheritance where neither allele completely dominates the other. The heterozygote expresses an intermediate phenotype.

Heterozygote

An organism that carries two different alleles for a particular gene.

Intermediate Phenotype

A phenotype that is between the two homozygous phenotypes.

Andalusian Chicken Feather Color

An example of incomplete dominance, where black and white alleles create blue-gray feathers in heterozygotes.

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Codominance

A type of inheritance where both alleles in a heterozygote are fully and equally expressed.

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Allele

One of the possible forms of a gene.

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Phenotype

The observable characteristics of an organism.

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Homozygous

An organism that has two identical alleles for a particular gene.

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Codominant Alleles

Alleles in a codominant relationship that are both expressed in the heterozygote.

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Blood type AB

A blood type resulting from the co-expression of both the A and B antigens on red blood cells.

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Sickle-cell anemia (codominance)

A genetic condition where both normal and mutated hemoglobins are produced, resulting in red blood cells that are both normal and sickle-shaped.

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Sickle cell trait

A condition where both normal and sickle-shaped red blood cells are present in the bloodstream, caused by the heterozygous genotype (HbAHbS).

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Recessive lethal gene

An allele that causes death only when two copies are inherited (homozygous).

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Sickling

The process where red blood cells change shape to a rigid, sickle form.

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HbA

Allele for normal hemoglobin.

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HbS

Allele for sickle-cell hemoglobin.

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Lethal genes

Genes that cause death when present in specific combinations.

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Embryonic lethality

Death occurring during embryonic development.

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Lethal Allele

An allele that causes death, usually before or soon after birth. It can be recessive or dominant.

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Recessive Lethal Allele

A type of lethal allele that leads to death only when present in two copies (homozygous).

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Dominant Lethal Allele

A type of lethal allele that leads to death even with just one copy (heterozygous).

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Why are dominant lethal alleles rare?

Individuals carrying a dominant lethal allele usually die before reaching reproductive age, making it difficult for the allele to be passed on.

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Phenotypic Ratio

The ratio of different physical traits observed in offspring, based on the expression of genes.

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Skewed Phenotypic Ratio

A phenotypic ratio that's different from the normal Mendelian ratios (like 3:1).

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Huntington's Disease

A genetic disorder caused by a dominant lethal allele that results in progressive brain degeneration. It's characterized by uncontrolled movements, cognitive decline, and emotional disturbances.

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Why does Huntington's disease affect individuals even later in life?

The dominant lethal allele responsible for Huntington's disease doesn't impact the individual's viability until after reproductive age.

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Dominant Lethal Gene

A gene that causes death when present in even one copy, even if the other allele is normal.

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Homozygous Lethal

An organism with two copies of a lethal gene, resulting in death.

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Heterozygous Carrier

An organism with one copy of a lethal gene and one copy of the normal allele, usually surviving but showing effects.

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Creeper Chicken

A breed of chicken with short legs due to a dominant lethal gene. Heterozygotes have short legs, while homozygotes die before hatching.

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Manx Cat

A cat breed known for its taillessness, caused by a dominant lethal gene. Homozygotes die, while heterozygotes are tailless.

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Achondroplasia Dwarfism

A genetic disorder causing dwarfism. Caused by a dominant allele, but homozygous individuals die before birth.

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Multiple Alleles

The existence of more than two alternative forms of a gene (alleles) for a particular trait within a population.

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Dominance Hierarchy

A ranking system within multiple alleles where some alleles exhibit complete dominance, partial dominance, or recessive traits relative to others. This creates complex inheritance patterns.

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Increased Phenotypic Variety

The presence of multiple alleles expands the range of possible physical traits (phenotypes) for a characteristic. This leads to greater diversity within a population.

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ABO Blood Group System

A classic example of multiple alleles. The ABO blood group is determined by three alleles: IA, IB, and i. These alleles determine the presence or absence of antigens on red blood cells.

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IA, IB, and i

The three alleles that determine ABO blood type: IA codes for the A antigen, IB codes for the B antigen, and i codes for no antigen (O blood type).

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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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Fundamentals Of Genetics Chapter 4 PDF

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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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