BIL 160 Exam 1# Hanna

Lecture #6: Evolution

When exactly is it that immune cells “evolve” in chordates such as humans? Be specific

after the introduction of a pathogen to the immune system

What is an antigen?

a part of a pathogen (not a part of the human body)

Why will evolution never “create” the perfect variant for any individual in any species?

No. Evolution in individuals is in a constant arms race with the evolution of pathogens

Define “arms race” in biology

In biology, an "arms race" refers to a continuous evolutionary competition between two or more species, characterized by reciprocal adaptations and counter-adaptations aimed at gaining advantage over each other.

What is the difference between clonal selection and clonal expansion? Do you really understand the difference between them?

• clonal expansion: the proliferation of a specific population of cells derived from a single ancestor, resulting in an increased number of identical cells.

• Clonal selection: a process in adaptive immunity where lymphocytes with receptors specific to a particular antigen are activated and undergo proliferation, leading to the production of a large number of effector cells targeted against that antigen.

Do asexual species look alike? In what way(s)?

They are completely identical in all ways. phenotypically and genotypically

How is it that sex creates new genetic variants? Explain

sex create new genetic variants because of the crossing over that occurs in the creation of the germ cells thus bringing together new combinations of genes

Do you understand how asexual species can change in frequency over time and how? What is the ultimate result in the evolution of such asexual populations?

asexual species can change in frequency over time due to mutations, genetic drift, and natural selections. The end result is death (extinction).

What types of environmental features affect the frequency of sexual and asexual “strains” within a species? Can you explain them briefly?

• asexual reproduction is favoured when: there is low environmental unpredictability, low number of niches, low parasite load

• sexual reproduction favoured: when there is high environmental unpredictability, high number of niches, high parasite load

Do you understand how escape variants work?

pathogens that escape the first treatments and have selective advantage in a population of hosts with immunological memory against previous strains

What are 3 features of rapidly evolving pathogens when studying them on a relationship tree?

no deep branches, a single trunk, rapidly evolving genotypes