Chapter 22: Introduction to Evolution (Part 2, Week 1) Flashcards
[The molecular processes that underlie evolution] What can researchers in evolutionary biology now analzye, with the advent of molecular approaches, to see associated changes?
They can analyze how changes in genetic material are associated with changes in phenotype.
Phenotypes are the set of observable characteristics or traits of an organism.
What are two or more genes derived from the same ancestral gene that have accumalated random mutations that make their sequences slightly different?
Homologous genes.
What do you call homologous genes found in different species?
Orthologs
Orthologs have similar gene sequences because they are derived from the same ancestral gene. The sequences are not identical because after the species diverged, each one accumulated different random mutations that changed their sequences.
Example: Consider a gene that encodes a transport protein involved in the uptake of metal ions into the cells of two different species of bacteria.
- Millions of years ago, the two species of bacteria had a common ancestor.
- This common ancestor diverged into two different species, eventually evolving into E.coli, C. cac, and many other species.
- Since the divergence, the gene encoding the transport protein has accumlated mutations that altered its sequence, though the similarity between E. coli and C. cac genes remain striking.
- The two sequneces are similar because they were derived from the same ancestral gene, but they are not identical due to the independent accumlation of different random mutations.
What are two or more homologous genes within a single species termed?
Paralogs
What is a group of homologous genes within a single species that carry out related functions?
Gene family
What is an example of a well-studied gene family in humans?
The globin gene family.
Comprised of 14 genes on three different chromosomes that are hypothesized to be derived from a single ancestral globin gene.
The advantages of gene families, in the care of globin, play a role in oxygen binding and allows these globin genes to be expressed at different stages of development during the embryonic, fetal, and postpartum stages of life.
For adaptation, these gene families have allowed terristial mammals to use internal gestation to protect their young instead of laying eggs like reptiles. The embryonic and fetal forms of hemoglobin allow the embryo and fetus to capture oxygen from the bloodstream of the mother.
What is a type of evolution in which genetic changes occur in a series of related species that form a lineage; species evolve from pre-existing species by the accumulation of mutations?
Vertical evolution (gene duplications and gene mutations)
What is a process in which an organism incorporates genetic material from another organism without being the offspring of that organism?
Horizontal gene transfer
Give an example of horizontal gene transfer?
Hint: Paramecium (eukaryotic microorganism)
- The paramecium engulfs a bacterial cell and degrades it in a phagocytic vesicle.
- A bacterial gene escapes to the nucleus of the host paramecium where it is inserted into one of the chromosomes.
- This gene has now transferred from a bacterial species to an eukaryotic species. By analyzing gene sequences of many different species, researches have discovered that horizontal gene transfer is a common phenomenon.
What are the three mechanisms of gene transfer that could result in horizontal gene transfer between two different bacterial species?
Conjugation, transformation, and transduction.
Conjugation - direct contact between a donor cell, who sends a plasmid, to a recipient cell that now has a plasmid.
Transformation - a fragment of DNA from a donor cell is released into the environment. This DNA fragment is taken up by a recipient cell, which incorporates the DNA into its chromosome.
Transduction - when a bacteriophage infects a donor cell, it causes the bacterial chromosome of the donor cell to break up into fragments. A fragment of bacterial chromosomal DNA is incorporated into a newly made bacteriophage. This bacteriophage then transfers this fragement of DNA to a recipient cell.
What percentage of variation in the genetic composition of modern bacterial species can be attributed to the process of horizontal gene transfer?
20-30%
These gene transfers are varied but most of them affect survival and reproduction (conferring antibiotic resistance, ability to degrade toxic compounds, and pathogenicity (ability to cause disease))
Other than vertical evolution and horizontal gene transfer, what other changes can affect evolution?
Changes in chromosome structure and number.
Comparisons of chromosomes of closely related species have revealed that changes in chromosome structure and/or number are common.
Fun fact: What is interesting about chromosome 2?
Humans have only one large chromosome 2 (second largest; 8% of total DNA) and is a result of an end to end fusion of two ancestral chromosomes.
Also, because of this, humans have 23 pairs of chromosomes while other hominidae have 24 pairs.
Review Concept Questions:
Heritable change in traits of a population from one generation to the next is called ______.
Evolution
Small-scale changes in a single gene or allele frequencies of a population are termed _______ , whereas large-scale patterns such as the formation of new species are referred to as __________
Microevolution and macroevolution
A group of related organisms that share a distinctive form constitute a(n) _______
species
Evolution is supported by a substantial body of evidence and explains a wide range of observations; thus it is considered a scientific ________
theory
Some scientists believe that nothing in biology makes sense unless viewed in the light of the theory of evolution; why?
Evolution provides a framework for understanding all of the diversity of life on Earth.
When did European scholars first begin to apply empirical and scientific thought to their study of biological phenomena?
The 1600s
A change in the allele frequencies of a population over three generations is an example of ______.
microevolution
Which observation was the basis of John Ray’s concept of a species?
Individuals of one species do not interbreed with individuals of another species.
Which of the following statements is typically used as a working definition of species?
A group of related individuals that share a distinctive form.
Why is evolution considered a theory? (2)
Because it is supported by a large body of evidence
Because it helps explain a very wide range of observations
The scientist who recorded information about the natural world on the voyage of the HMS Beagle and developed a theory that existing species have evolved from pre-existing species was __________ __________.
Charles Darwin
Why is the theory of evolution a unifying theme in biology?
It explains the diversity of life.
Individuals with heritable traits that make them better suited to their native environment tend to flourish and reproduce more than others. This process is called ______.
Natural Selection
