AP® Biology Crash Course, For the New 2020 Exam, Book + Online by Michael D'Alessio

Author:Michael D'Alessio
Language: eng
Format: epub
Publisher: Research & Education Association
Published: 2019-03-17T16:00:00+00:00

Know the names, descriptions, and effects of the different types of mutations.

III. Genetic Variation in Prokaryotes and Viruses

A.Prokaryotes reproduce asexually, but they also have several methods of genetic recombination.

1.Transformation occurs when a prokaryote takes up foreign DNA from its environment.

2.Transduction is when a virus transfers prokaryotic DNA from one cell to another.

3.Conjugation occurs when a plasmid is transferred from one prokaryote to another through a special tube-like structure called a pilus.

B.Because prokaryotes have a very short generation time, mutation and genetic recombination play important roles in producing and maintaining genetic diversity.

C.Virus replication involves invading a host cell and eventually living off of the host by taking over the metabolic machinery (parasitic).

1.Viruses cannot reproduce independently.

2.Viruses attach to the host via cell surface receptors and inject their DNA into the host.

3.During the lytic cycle, which is a type of viral reproduction, the virus eventually kills the host.

4.During the lysogenic cycle, the virus replicates its genome without killing the host and forms prophage (incorporation of the viral DNA into the host chromosome).

D.Viruses are efficient at rapid evolution and acquiring new phenotypes. The wide variety of possible hosts, and in turn, the enormous possibilities of chromosomes and their respective genes through which a virus can replicate itself all contribute to viruses’ abilities to possess the potential for expansive genetic variations.

E.HIV, the causative agent of acquired immunodeficiency syndrome (AIDS), is a retrovirus; it uses an enzyme called reverse transcriptase to synthesize DNA from an RNA strand and infects T4 helper cells.

F.Prion is the protein infectious particle or misfolded protein that converts other normal proteins into mutant form; it is also the causative agent for “mad cow disease.”

IV. Variation Due to Sexual Reproduction

A.Sexual reproduction produces genetic variation in three ways: independent assortment of homologous chromosomes, crossing over, or random fertilization.

B.The first two genetic recombination events occur during meiosis I.

1.Independent assortment of homologous chromosomes—occurs during metaphase I and anaphase I, creating a variety of outcomes (gametes) that contain different combinations of an organism’s maternal and paternal chromosomes.

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