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Chapter 3

Chapter 3 Summary Understanding Humans

Course Code
ANTH 1026F/G
Andrew Nelson

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Chapter Three: Heredity and Evolution:
-Cells are the fundamental units of life and they are essentially classified into two types
-Somatic cells make up body tissues
-Gametes (eggs and sperm) are reproductive cells that transmit genetic information from
parent to offspring
-Genetic information is sound in DNA molecules that are in the nuclei of cells
-DNA is capable of replication and during mitosis and meiosis this is a key factor that makes
it possible for daughter cells to receive the correct amount of DNA to be able to function
-DNA controls protein synthesis by directing cells to arrange amino acids in the proper
sequence for each particular protein
-RNA is a similar molecule which is also used on protein synthesis
-Cells multiply by dividing and during cell division DNA is visible under a microscope in the
form of chromosomes
-In humans there are 46 chromosomes, 23 from each parent
-Somatic cells divide during growth or tissue repair or replace old or damaged cells
-Somatic cell division is called mitosis
-During mitosis a cell divides one time to produce two daughter cells that each possess a full
and identical set of chromosomes
-Sex cells are produced when specialized cells in the ovaries and testes divide during
-Meiosis is characterized by two divisions that produce four non-identical daughter cells that
each have only half the amount of DNA (23 chromosomes) contained within the original cell
-Gregor Mendel discovered the principles of segregation, independent assortment, and
dominance and recessiveness by doing experiments with pea plants
-Characteristics influenced by only one genetic locus are called Mendelian traits (ABO blood
type is a human example)
-Many characteristics including stature and skin colour are polygenic meaning that they are
influenced by more than one genetic locus and show continuous range of expression
-Building on 19th century contributions of Darwin and the rediscovery of Mendel’s work in
1900 advances in genetics throughout the 20th century contributed to contemporary
evolutionary thought
-The combination of natural selection with Mendel’s principles of inheritance and
experimental evidence concerning the nature of mutation have all been synthesized into a
modern understanding of evolutionary change called “Modern Synthesis”
-In this contemporary theory of evolution evolutionary change is seen as a two stage
-The first stage is the production and redistribution of genetic variation and the second is the
process whereby natural selection acts on that variation
-Mutation is crucial to all evolutionary change because it is the only source of completely
new genetic material which increases variation
-Natural selection is the crucial factor that influences the long term direction of evolutionary
-How natural selection works can best be explained as differential net reproductive success
or how successful individuals are in producing offspring for succeeding generations
-Genetic drift which is the random loss of alleles due to small population size and gene flow
which is the exchange of genes between populations are also very important in evolutionary
-The expression of all biological traits is to varying degrees under genetic control
-Genes then can be said to set limits and potentials for human growth, development, and
-These limits and potentials are not written in stone because many characteristics are also
very much influenced by such environmental factors as temperature, diet, and sunlight
-Ultimately it is the interaction between genetic and environmental factors that produce
phenotypic variation and evolutionary change in all species
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