Genetics Lecture 3: Lethal Genes
39 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What temperature is lethal for the Kidney-eyed mutant of the wasp Bracon hebetor?

  • 8°C
  • 25°C
  • 30°C (correct)
  • 19°C

In a balanced lethal system, what proportion of the offspring will survive?

  • 25%
  • 50% (correct)
  • 75%
  • 100%

What type of genes lead to the inviability of gametes?

  • Gametic lethals (correct)
  • Semilethal genes
  • Balanced lethal genes
  • Conditional lethal genes

Which of the following plants is known to have a chlorophyll mutant that can produce albino seedlings?

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

In a balanced lethal system, what alleles are linked together on the same chromosome?

<p>Recessive lethal alleles and normal alleles (C)</p> Signup and view all the answers

What happens to 25% of the zygotes in a balanced lethal system?

<p>They are homozygous for one of the lethal alleles and do not survive (B)</p> Signup and view all the answers

Semilethal genes cause the death of what percentage of individuals that carry them?

<p>More than 90% (B)</p> Signup and view all the answers

What effect does a conditional lethal gene exert based on temperature?

<p>Requires specific conditions to be lethal (A)</p> Signup and view all the answers

In terms of gametic lethals, what is the outcome commonly referred to when there is a complete absence in expected ratios?

<p>Segregation distortion (C)</p> Signup and view all the answers

What characterizes a lethal gene?

<p>It causes the death of individuals with the proper genotype before adulthood. (B)</p> Signup and view all the answers

In what state does a recessive lethal gene express its effects?

<p>In homozygous state only. (D)</p> Signup and view all the answers

Which of the following is not a category of lethal genes?

<p>Semi-lethal genes (B)</p> Signup and view all the answers

What genotype results in the yellow coat color in mice, which is lethal?

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

Which type of lethal gene is most common?

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

What percentage of embryos from yellow mice is typically unviable?

<p>25% (C)</p> Signup and view all the answers

What is the proper genotype for a recessive lethal gene that affects survival?

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

What occurs during the embryonic development of homozygous YY mice?

<p>They die at an early embryonic stage. (C)</p> Signup and view all the answers

What is a defining property of dominant lethal genes?

<p>They are expressed in both homozygous and heterozygous states. (C)</p> Signup and view all the answers

Which of the following statements is true regarding lethal genes?

<p>Recessive lethals affect survival only in homozygous states. (D)</p> Signup and view all the answers

What are subvital genes?

<p>Genes that reduce viability but kill less than 90% of individuals. (B)</p> Signup and view all the answers

Which of the following is an example of a supervital gene?

<p>Genes for disease resistance (B)</p> Signup and view all the answers

Which genes are considered vital genes?

<p>All wild type alleles of an organism's genes. (C)</p> Signup and view all the answers

What is a characteristic of supervital genes?

<p>They may confer resistance to abiotic stresses. (B)</p> Signup and view all the answers

How do subvital genes primarily affect individuals?

<p>They reduce viability but do not completely eliminate the individuals. (C)</p> Signup and view all the answers

Which of the following traits is NOT associated with vital genes?

<p>They can increase the likelihood of disease resistance. (A)</p> Signup and view all the answers

What can be inferred about mutant genes in general?

<p>Most mutant genes tend to be subvital. (D)</p> Signup and view all the answers

What distinguishes supervital genes from other genes?

<p>They enhance survival under specific conditions. (A)</p> Signup and view all the answers

In what condition are xantha mutants described?

<p>They are semilethal in the homozygous state. (A)</p> Signup and view all the answers

What does the term 'homozygous state' refer to?

<p>Having identical alleles for a gene. (D)</p> Signup and view all the answers

What is a characteristic of recessive genes in relation to their phenotypic effects?

<p>They cause normal phenotype and survival in heterozygous individuals. (C)</p> Signup and view all the answers

How do albino seedlings in barley behave in terms of phenotype?

<p>They survive on stored food as they cannot photosynthesize. (C)</p> Signup and view all the answers

What do zygotic lethal genes affect?

<p>Survival rates of zygotes with specific genotypes. (D)</p> Signup and view all the answers

Which of the following is true about dominant lethal alleles?

<p>They cause lethality in both homozygous and heterozygous states. (C)</p> Signup and view all the answers

What is Huntington's disease characterized by?

<p>It has onset usually in a person's thirties or forties. (B)</p> Signup and view all the answers

What are conditional lethals?

<p>Genes that behave normally unless certain conditions are met. (C)</p> Signup and view all the answers

Which gene is an example of a dominant lethal in humans?

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

What ratio of green to albino seedlings is expected shortly after germination in barley?

<p>3:1 (B)</p> Signup and view all the answers

Why cannot dominant lethal alleles be maintained in a population?

<p>Affected individuals die before reproducing. (A)</p> Signup and view all the answers

How does a dominant lethal gene impact heterozygous individuals?

<p>They experience severe health conditions and early death. (A)</p> Signup and view all the answers

Flashcards

Lethal Gene

A gene whose presence in the homozygous state leads to the death of the organism before it reaches adulthood.

Recessive Lethal

A type of lethal gene where the effect is only expressed when the organism inherits two copies of the gene (homozygous state).

Dominant Lethal

A type of lethal gene where the effect is expressed even when the organism inherits only one copy of the gene (heterozygous state).

Conditional Lethal

A type of lethal gene where the effect is triggered by specific environmental conditions.

Signup and view all the flashcards

Balanced Lethal

A type of lethal gene where the effect is balanced by another gene, leading to the survival of heterozygotes.

Signup and view all the flashcards

Gametic Lethal

A type of lethal gene that affects the survival of gametes (sex cells).

Signup and view all the flashcards

Yellow Coat Color in Mice

The yellow coat color in mice is caused by a dominant gene, but this gene is also a recessive lethal.

Signup and view all the flashcards

YY Genotype in Mice

The homozygous dominant genotype (YY) for yellow coat color in mice is lethal, resulting in embryonic death.

Signup and view all the flashcards

25% Embryonic Death

The observed 25% death rate in embryos of yellow mice mated to yellow mice supports the recessive lethal nature of the yellow coat color gene in mice.

Signup and view all the flashcards

Yellow Coat Color as a Recessive Lethal

The yellow coat color gene in mice is a classic example of a recessive lethal gene.

Signup and view all the flashcards

Recessive Lethal Gene

A recessive gene that causes death in homozygous individuals but allows normal survival in heterozygotes.

Signup and view all the flashcards

Conditional Lethal Gene

A gene that produces a lethal effect only under specific environmental conditions.

Signup and view all the flashcards

Dominant Lethal Gene

A gene that causes death in both homozygous and heterozygous individuals.

Signup and view all the flashcards

Epiloia

A condition caused by a dominant lethal gene that results in abnormal skin growths, severe mental defects and multiple tumors in individuals.

Signup and view all the flashcards

Huntington's Disease

A progressive brain disorder caused by a dominant lethal gene that results in uncontrolled movements, emotional problems, and loss of thinking ability.

Signup and view all the flashcards

Lethal Effect Stage

The stage of development at which a lethal gene produces its lethal effect.

Signup and view all the flashcards

Early Embryonic Lethal Gene

A gene that is responsible for the death of an embryo at a very early stage of development.

Signup and view all the flashcards

Late-Acting Lethal Gene

A gene that allows an organism to survive and develop close to the reproductive age.

Signup and view all the flashcards

Heterozygote for a Lethal Gene

An individual carrying one copy of a lethal gene, but exhibiting a normal phenotype and survival.

Signup and view all the flashcards

Homozygote for a Lethal Gene

An individual with two copies of a lethal gene, resulting in a lethal phenotype.

Signup and view all the flashcards

Temperature-Sensitive Lethal Gene

A gene that is lethal only under specific environmental conditions (like temperature).

Signup and view all the flashcards

Bi-directional Temperature-Sensitive Lethal

A lethal gene that works in both directions. It's lethal at a high temperature, but also at a very low temperature.

Signup and view all the flashcards

Semilethal Gene

A lethal gene that doesn't always kill all individuals carrying it, but causes death in more than 90% of them.

Signup and view all the flashcards

Segregation Distortion

The phenomenon where the expected normal ratios of offspring are distorted due to gametic lethals, which eliminates certain gametes before fertilization.

Signup and view all the flashcards

Recessive Lethal (simple definition)

A lethal gene that causes death only when both copies of the gene are present.

Signup and view all the flashcards

Perpetual Heterozygosity

In balanced lethal systems, the genes closely linked to the lethal genes are always inherited in a heterozygous state.

Signup and view all the flashcards

Semilethal Gene (simple definition)

A gene that causes death in more than 90% of individuals carrying the gene.

Signup and view all the flashcards

Subvital Gene

Genes that cause a reduction in the viability of an organism but don't necessarily lead to death. These genes cause less than 90% mortality in individuals carrying the mutant allele.

Signup and view all the flashcards

Vital Gene

A gene that does not have a significant effect on the survival of an organism, neither enhancing nor reducing its viability.

Signup and view all the flashcards

Supervital Gene

Mutant alleles that actually increase the survival rate of organisms that carry them in the correct genotype.

Signup and view all the flashcards

What are subvital genes? Give an example.

A gene that causes a reduction in the viability of individuals and kills less than 90% of the individuals carrying them. Example: the Viridis mutant in barley.

Signup and view all the flashcards

Study Notes

Lecture 3: Lethal Genes

  • Lethal genes impact the survival of zygotes/individuals with a specific genotype.
  • Equal survival of all gametes and zygotes is a fundamental assumption of inheritance.
  • Lethal genes are grouped into five categories:
    • Recessive lethals: Effects only in the homozygous state; heterozygotes are unaffected.
    • Dominant lethals: Kill both homozygous and heterozygous individuals.
    • Conditional lethals: Lethal only under specific conditions (e.g., temperature).
    • Balanced lethals: Linkage of multiple lethal genes causes heterozygotes to survive while homozygotes die.
    • Gametic lethals: Effect is on gamete viability and results in non-typical ratios in offspring.
  • Semilethal genes: Cause death in more than 90% of individuals carrying them in the proper genotype.
  • Subvital genes: Reduce viability, but less than 90% of individuals carrying them die.
  • Vital genes: Do not impact survival in any genotype.
  • Supervital genes: Enhance the survival of individuals carrying them.

Recessive Lethals

  • Most lethal genes are recessive lethals.
  • Effects are only expressed in the homozygous state (e.g., yellow coat color in mice).
  • Heterozygotes with only one recessive copy of the lethal gene are normal.
  • Examples include mice with yellow coat color (Yy heterozygotes survived while YY homozygotes died), and albino seedlings in barley.

Dominant Lethals

  • Dominant lethal alleles are lethal in both homozygous and heterozygous states (e.g., Huntington's disease, epiloia).
  • Examples include epiloia, and Huntington's disease.
  • Cannot persist in the population unless continually produced by mutation.

Conditional Lethals

  • Lethal only under specific conditions or temperatures.
  • Example (Kidney-eyed mutant): Normal development at lower temperatures, but lethal at higher temperatures. A similar example is found in chlorophyll mutants of barley.

Balanced Lethals

  • Linkage of multiple lethal genes causes only the heterozygotes in the progeny to survive.
  • Homozygotes will not survive, therefore the only possible surviving progeny are heterozygotes.

Gametic Lethals

  • Lethal genes affect gamete viability.
  • Result in the complete disappearance of one class of gamete or phenotype in segregating generations.
  • Example phenomenon is known as segregation distortion or meiotic drive.

Semilethal Genes

  • Cause death in more than 90% of affected individuals.

Subvital Genes

  • Reduce viability.
  • Cause death of less than 90% of individuals carrying them in the proper genotype.

Vital Genes

  • Do not affect the survival of individuals. Examples are wild-type alleles in an organism.

Supervital Genes

  • Enhance the survival of individuals.
  • Examples include genes for resistance to disease and abiotic stresses (e.g., salinity, drought). These may enhance plant fitness during stress.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Lecture 3: Lethal Genes (PDF)

Description

Explore the concept of lethal genes and their classifications in this quiz. Understand how different types of lethal genes, including recessive, dominant, and conditional lethals, impact survival and genetic inheritance. This lecture emphasizes the implications of these genes on zygotes and overall genetic viability.

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser