Biological and Biochemical Foundations of Living Systems: Content Category 1C

Transmission of heritable information from generation to generation and the processes that increase genetic diversity

The information necessary to direct life functions is contained within discrete nucleotide sequences transmitted from generation to generation by mechanisms that, by nature of their various processes, provide the raw materials for evolution by increasing genetic diversity. Specific sequences of deoxyribonucleic acids store and transfer the heritable information necessary for the continuation of life from one generation to the next. These sequences, called genes ― being part of longer DNA molecules ― are organized, along with various proteins, into biomolecular assemblies called chromosomes.

Chromosomes pass from parents to offspring in sexually-reproducing organisms. The processes ofmeiosis and fertilization maintain a species’ chromosome count during the sexual life cycle. Because parents pass on discrete heritable units that retain their separate identities in offspring, the laws of probability can be used to predict the outcome of some, but not all, genetic crosses.

The behavior of chromosomes during meiosis and fertilization is responsible for most of the genetic variation that arises each generation. Mechanisms that contribute to this genetic variation include independent assortment of chromosomes, crossing over, and random fertilization. Other mechanisms, such as mutation, random genetic drift, bottlenecks, and immigration, exist with the potential to affect the genetic diversity of individuals and populations. Collectively, the genetic diversity that results from these processes provides the raw material for evolution by natural selection.

The content in this category covers the mechanisms by which heritable information is transmitted from generation to generation, and the evolutionary processes that generate and act upon genetic variation.

Topic Level Key

The abbreviations found in parentheses indicate the course(s) in which undergraduate students at many colleges and universities learn about the topics and associated subtopics. The course abbreviation is:

BIO = two-semester sequence of introductory biology

Please note topics that appear on multiple content lists will be treated differently. Questions will focus on the topics as they are described in the narrative for the content category.

Evidence that DNA is Genetic Material (BIO)

Mendelian Concepts (BIO)

• Phenotype and genotype

• Gene

• Locus

• Allele: single and multiple

• Homozygosity and heterozygosity

• Wild-type

• Recessiveness

• Complete dominance

• Co-dominance

• Incomplete dominance, leakage, penetrance, expressivity

• Hybridization: viability

• Gene pool

Meiosis and Other Factors Affecting Genetic Variability (BIO)

• Significance of meiosis

• Important differences between meiosis and mitosis

• Segregation of genes

  • Independent assortment

  • Linkage

  • Recombination

    • Single crossovers

    • Double crossovers

    • Synaptonemal complex

    • Tetrad

  • Sex-linked characteristics

  • Very few genes on Y chromosome

  • Sex determination

  • Cytoplasmic/extranuclear inheritance

  • Mutation

    • General concept of mutation - error in DNA sequence

    • Types of mutations: random, translation error, transcription error, base substitution, inversion, addition, deletion, translocation, mispairing

    • Advantageous vs. deleterious mutation

    • Inborn errors of metabolism

    • Relationship of mutagens to carcinogens

  • Genetic drift

  • Synapsis or crossing-over mechanism for increasing genetic diversity

Analytic Methods (BIO)

• Hardy–Weinberg Principle

• Testcross (Backcross; concepts of parental, F1, and F2 generations)

• Gene mapping: crossover frequencies

• Biometry: statistical methods

Evolution (BIO)

• Natural selection Fitness concept

  • Selection by differential reproduction

  • Concepts of natural and group selection

  • Evolutionary success as increase in percent representation in the gene pool of the next generation

• Speciation

  • Polymorphism

  • Adaptation and specialization

  • Inbreeding

  • Outbreeding

  • Bottlenecks

• Evolutionary time as measured by gradual random changes in genome

Additional Review: Khan Academy MCAT^® Collection Tutorials

To support your studies, see the following video tutorials below from the Khan Academy MCAT Collection. The videos and associated questions were created by the Khan Academy in collaboration with the AAMC and the Robert Wood Johnson Foundation.