Natural Selection and Polyploidy in Drosophila

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Questions and Answers

What is the process that gives rise to most allopolyploids?

Uniparental disomy

Clonal reproduction

Hybridization followed by chromosome doubling (correct)

Chromosome fragmentation

What role does polyploidy play in the colonization of new environments?

It solely increases plant size.

It restricts populations to specific climates.

It reduces genetic variation in populations.

It enhances adaptability to diverse habitats. (correct)

In the common garden experiment with Achillea borealis, which plants were monitored for survival?

Diploid and hexaploid plants

Tetraploid and neo-hexaploid plants (correct)

Allopolyploid and diploid plants

Only hexaploid plants

Which environment is associated with tetraploid populations of Achillea borealis?

Mountain meadows Signup and view all the answers

How does genome duplication generally affect plant adaptation?

It enhances the ability to survive in various environments. Signup and view all the answers

What is the effect of natural selection on body size in fly populations according to the findings?

Natural selection favors large flies in cold, wet climates. Signup and view all the answers

How does polyploidy affect genetic variation in organisms?

It can lead to the formation of new species. Signup and view all the answers

What is a consequence of failed segregation during meiosis that can result in polyploidy?

An increase in the number of chromosomes. Signup and view all the answers

Which of the following is NOT a way polyploidy is important in evolution?

It consistently decreases organism size. Signup and view all the answers

What is one way that inversions in Drosophila are related to adaptation?

They impact gene regulation affecting body size. Signup and view all the answers

Which of these statements about clines and body size in fly populations is accurate?

Pronounced and parallel clines exist in multiple continents. Signup and view all the answers

What does polyploidy alter in organisms that can contribute to evolution?

It increases chromosome number leading to new adaptations. Signup and view all the answers

What role do the inversions in Drosophila play in relation to climate adaptation?

They lock certain genes influencing body size for survival. Signup and view all the answers

What is a nonsynonymous (or replacement) substitution mutation?

A mutation that changes the amino acid specified by a codon. Signup and view all the answers

How do new genes, such as those associated with chondrodysplasia, typically arise in organisms?

By unequal crossing over during meiosis. Signup and view all the answers

What distinguishes paralogous genes from orthologous genes?

Paralogous genes arise from gene duplication within the same species. Signup and view all the answers

Which process can lead to the creation of new alleles in a population?

Polyploidy Signup and view all the answers

What is a synonymous (or silent) substitution mutation?

A mutation that leaves the encoded protein unchanged. Signup and view all the answers

What is the result of mutations that are not repaired and become premutations?

They eventually lead to changes in evolutionary fitness. Signup and view all the answers

Which mechanism is most associated with the generation of genes from scratch?

Gene duplication through retroposition. Signup and view all the answers

How does genome duplication influence phenotypic adaptation?

It can provide raw material for evolution by creating genetic redundancy. Signup and view all the answers

Study Notes

Cline Evidence for Natural Selection

Cline patterns in Drosophila body size are consistent across North America, South America, and Europe.
These parallel clines demonstrate that the body size variation is not a result of historical accident but is driven by natural selection.
Larger flies are favored in cold, wet climates, while smaller flies are favored in hot, dry areas.
Genes located in inversions play a role in influencing body size.

Genome Duplication and Polyploidy

Polyploidy, the condition of having more than two sets of chromosomes, can arise due to errors in meiosis (meiosis I or II).
Polyploidy can lead to the formation of new species by altering cell size, geometry, and gene dosage, resulting in novel phenotypes.

Polyploidy and Speciation

Most allopolyploids result from hybridization between two species followed by chromosome doubling.
Polyploidy facilitates adaptation to new environments.
A common garden experiment with Achillea borealis showed that tetraploid populations thrive in coastal grasslands, conifer forests, and mountain meadows, while hexaploid populations are found in sand dunes and oak woodlands.

New Alleles and Gene Formation

Mutations are changes in the DNA sequence.
Spontaneous deamination is a common type of mutation that can lead to new alleles.
Premutations are DNA alterations that are susceptible to repair.

Mutation Effects on Protein Function

Mutations can lead to changes in the encoded protein, impacting its structure and function.
Synonymous (silent) substitutions are mutations that do not change the encoded amino acid.
Nonsynonymous (replacement) substitutions alter the amino acid specified by a codon, potentially affecting protein function.

Mechanisms of Gene Duplication

Gene duplication is a major source of new genes.
Unequal crossing over: During meiosis, misalignment of homologous chromosomes can result in one chromosome gaining DNA and the other losing it, creating a duplicate copy of a gene.
Retroposition: A copy of an mRNA molecule is reverse transcribed into DNA and inserted into the genome, creating a new gene.

Example of Gene Duplication:

A duplicate copy of the gene for fibroblast growth factor 4 (fgf4) is found in some dog breeds, contributing to chondrodysplasia, a condition characterized by short legs.

New Genes from Scratch

C22orf45 is a gene with an unknown function that is unique to humans.
The appearance of entirely new genes is rare but a significant evolutionary process.

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Description

This quiz explores the evidence for natural selection through cline patterns in Drosophila body size across different climates. It also delves into the concepts of genome duplication and polyploidy, discussing their roles in speciation and adaptation. Test your understanding of these evolutionary processes!