Problem 9 - Campbell Biology Concepts & Connections

Question

Which of the following could provide the best data for determining the phylogeny of very closely related species? a. the fossil record b. their morphological differences and similarities c. a comparison of nucleotide sequences in homologous genes and mitochondrial DNA d. a comparison of their ribosomal DNA sequences

Step-by-Step Solution

Answer

c. a comparison of nucleotide sequences in homologous genes and mitochondrial DNA

Step 1 - Understand Phylogeny

Phylogeny refers to the evolutionary history and the relationships among a group of organisms. To determine phylogeny, scientists compare various types of data to deduce how closely related different species are.

Step 2 - Evaluate the Fossil Record

While the fossil record can provide insights into the evolutionary past, it might not be the most reliable source for determining the phylogeny of very closely related species due to gaps and lack of molecular detail.

Step 3 - Assess Morphological Differences and Similarities

Morphological data involves the comparison of physical traits. However, closely related species might exhibit very minimal morphological differences, making it difficult to discern their exact relationships.

Step 4 - Consider Nucleotide Sequences in Homologous Genes and Mitochondrial DNA

Comparing nucleotide sequences in homologous genes and mitochondrial DNA provides a high-resolution method for distinguishing between very closely related species. These sequences tend to accumulate mutations at a steady rate, which can be traced and compared.

Step 5 - Evaluate Ribosomal DNA Sequences

Ribosomal DNA sequences also mutate at a relatively steady rate and can be used for phylogenetic studies. However, for closely related species, mitochondrial DNA may provide more detailed and accurate data.

Step 6 - Conclusion

Among the options, the comparison of nucleotide sequences in homologous genes and mitochondrial DNA provides the best data for determining the phylogeny of very closely related species due to its high-resolution capability.

Key Concepts

evolutionary relationships

Understanding evolutionary relationships is crucial in biology. These relationships tell us how different species are related to each other through common ancestors. Scientists use various data types to determine these relationships, including morphological traits, genetic information, and fossil records. However, when studying closely related species, genetic data, especially from nucleotide sequences in homologous genes and mitochondrial DNA, can provide more precise insights.
Evolutionary relationships help construct phylogenetic trees.
These trees illustrate the links between different organisms, showing how they have diversified from common ancestors.
By analyzing these trees, scientists can trace the evolutionary paths of species over time.

nucleotide sequences

Nucleotide sequences are the building blocks of DNA and RNA. They consist of four bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The order of these bases in a DNA molecule forms the genetic instructions for the development and functioning of living organisms. For phylogenetic studies, comparing the nucleotide sequences in homologous genes is very effective.
Closely related species will have more similar nucleotide sequences due to their common genetic heritage.
Some key points about nucleotide sequences:

• They provide detailed genetic data.
• They can be used to calculate mutation rates.
• They help in identifying genetic similarities and differences among species.

Using these sequences can reveal even subtle evolutionary differences, offering a high-resolution approach to studying relationships among species.

homologous genes

Homologous genes are genes that are derived from a common ancestral gene. They can be very useful for understanding evolutionary relationships. When two species have homologous genes, it indicates they share a recent common ancestor.
Studying these genes can help reveal how species have evolved over time. Homologous genes can be either orthologous or paralogous.

• Orthologous genes: These occur in different species and perform the same function.
• Paralogous genes: These occur within the same species but may have different functions due to gene duplication.

By comparing these genes, scientists can deduce evolutionary events such as gene duplication, speciation, and functional diversification. This makes homologous genes a powerful tool in phylogenetic studies, especially when comparing very closely related species.

mitochondrial DNA

Mitochondrial DNA (mtDNA) is a small circular DNA found in the mitochondria, the energy-producing structures within cells. It is inherited almost exclusively from the mother, making it a valuable tool for studying maternal lineage.
Unlike nuclear DNA, mtDNA evolves rapidly, accumulating mutations at a relatively steady rate. This makes it particularly useful for studying evolutionary relationships among closely related species.
Some advantages of using mtDNA include:

• High mutation rate: Offers high resolution for recent evolutionary events.
• Maternal inheritance: Simplifies lineage tracing without recombination.
• Abundance: Cells contain many mitochondria, providing ample DNA for analysis.

By comparing mtDNA sequences, scientists can identify genetic similarities and differences that reveal the evolutionary history of closely related species. This method is often preferred for its precision and reliability.