Chapter 2 Biology and Evolution

Chapter Outline  What is Evolution?  What are the forces responsible for Evolution?  What is the molecular basis for Evolution?

Linnaeus Classification System  Body structure  Body function  Sequence of bodily growth

Classification of Humans KingdomAnimalia PhylumChordata SubphylumVertebrata ClassMammalia OrderPrimates

Classification of Humans SuperfamilyHominoidea FamilyHominidae SubfamilyHomininae GenusHomo Speciessapiens

Natural Selection Based on two observations:  All organisms display a range of variation.  All organisms have the ability to expand beyond their means of subsistence.

Evolution  Occurs as genetic variants in the gene pool of a population change in frequency.  Genes, the units of heredity, are segments of molecules of DNA (deoxyribonucleic acid).

DNA

Human DNA  Provides the instructions for the thousands of proteins that keep us alive and healthy.  Molecules are able to produce exact copies of themselves.  DNA molecules are located on chromosomes, structures found in the nucleus of each cell.

Chromosomes  Each organism has a characteristic number of chromosomes, usually found in pairs.  Humans have 23 pairs.  Genes located on paired chromosomes and coded for different versions of the same trait are called alleles.

Structure of a Generalized Eukaryotic Cell

Cell Division

Mendel’s Law of Dominance and Recessiveness  Dominant alleles are able to mask the presence of recessive alleles.  The allele for type A blood in humans, is dominant to the allele for type O blood.  Alleles that are both expressed when present are co-dominant.  An individual with the alleles for type A and type B blood has the AB blood type.

Evolutionary Forces  Mutation - happens when copying mistakes are made during cell division.  Genetic drift - the effect of chance events on the gene pool of small populations.  Gene flow - the introduction of new alleles from nearby populations.

Evolutionary Forces  Interspecies gene transfer - the transfer of genes between unrelated organisms.  Natural selection - the environment exerts pressure that selects individuals to reproduce the next generation.