ANTB14 Ch 2.docx

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University of Toronto Scarborough
Michael Schillaci

* = Exam question Introduction to Evolutionary Anthropology – Shawn M. Lehman Chapter 2: Microevolution and Evolutionary Anthropology Microevolution – small changes in biological evolution Genetic Basis of Inheritance and Biological Evolution Chromosomes and Genetic Materials There are two kinds of cells: prokaryotic and eukaryotic Prokaryotic cells  Lack nucleus  Unicellular Eukaryotic cells  Has a nucleus  Can either be unicellular or multicellular Chromosomes are located within the nucleus of a eukaryotic cell. Chromosomes are DNA (hereditary information/ molecules containing genes). Mitosis is when a parent cell divides into two diploid daughter cells (replicate cells). 2 processes: DNA replication and cell division Meiosis (haploid) - cellular division resulting in each daughter cell receiving half the amount of DNA as the parent cell (reproduction in organisms such as humans) Gamete – sex cell Humans – 23 pairs of chromosomes in a diploid cell (cell containing 2 chromosomes one inherited from each parent) XX = female XY = male – sex chromosomes Each gamete contains 22 autosomes Autosomes are responsible for all the phenotypic features (chromosomes not involved in determining sex of the organism) Different organisms have different numbers of chromosomes (48 = chimps) Recombination – the process by which two homologous chromosomes exchange genetic material during gamete formation DNA – deoxyribonucleic acid DNA is in the shape of a double stranded helix The DNA has a sugar-phosphate backbone The DNA is made up four different nucleotides 1. Adenine (A) 2. Cytosine (C) 3. Guanine (G) 4. Thymine (T) A and T pair up and are held together by 3 Hydrogen bonds C and G pair up and are held together by 2 Hydrogen bonds Therefore the H bonds between the C and G are weaker DNA is coiled into histones, which makes up chromosomes The telomere caps the ends of the chromosome to prevent damage. 1 * = Exam question Protein formation consists of transcription and translation RNA – single- stranded nucleic acid Transcription – copy the DNA info and take that info out of the cytoplasm. 1. DNA strands are separated 2. RNA copies the nucleotides (the thymine are replaced by uracil) Uracil replaces thymine to protect the genetic information 3. The mRNA carriers the copied genetic information out of the nucleus to the cytoplasm Translation – the information from the mRNA is used to construct proteins Ribosomes attach to the mRNA and moves across the genetic information. tRNA reads the information and brings in/places the anticodon (contains the amino acids). The base pairs are grouped in threes and one group is referred to as a codon (CCA). Each codon will code for a specific amino acid. The amino acids are placed next to one another by having the appropriate anticodon attached to the tRNA (GGT) Once the anti codon matches with the codon the amino acid associated with that anticodon will form a polypeptide bond with the previous amino acid. 2 * = Exam question Mutation: the Ultimate Source of Genetic Variation Mutation – an error or alternation of a nucleotide sequence, which represents the ultimate source of new genetic material in population (random process) Mutations can arise from (4) 1. Copying errors in the genetic material during cell division 2. Exposure to UV or ionizing radiation 3. Chemical mutagens 4. Viruses 2 classes of mutation 1. Somatic cell – any cells in the body that are not sperm or egg cells (cannot be passed through the generations) 2. Germ cell – sex cells (can be passed on and therefore does have an impact on the evolutionary process) Mutations can either be harmful, beneficial, or neutral (no effect) Neutral mutation is the most common form and has no effect because although the nucleotide is different it still codes for the same amino acid. Ex: GCU if the last nucleotide is switched to G so that the codon becomes GCG it still codes for the same amino acid = alanine Harmful mutations are usually eliminated from the population by the death of the individual. The beneficial mutation is somewhat rare in humans and example is a mutation in CKR5 gene, which provides some immunity from HIV. Hypothetical Mutation: Antibiotic Resistance in Bacteria There is a variance in bacteria that vary their resistance to certain drugs When antibiotics are used to combat bacteria The low antibiotic resistant bacteria are killed Which leaves just the high resistant bacteria The high resistant bacteria reproduce and form a population made up of bacteria that have high resistance to the antibiotics (drug resistance) Discontinuous variation – phenotypic variation that falls into discrete categories (they are physical appearances that are either displayed or not (green or yellow peas)) Continuous variation – phenotypic variation that falls along a continuum rather than in discrete units or categories (weight, height) Polygenic – a trait that results from the interaction of multiple genes (skin colour) Pleiotropic – the phenotypic effect of a single gene on more than one trait 3 * = Exam question Population Genetics Population – all the individuals of a particular species within a defined area Population genetics – the study of distribution of allele frequencies and changes under the influence of the four main mechanisms of evolution: mutation, genetic drift, gene flow, and natural selection Genetic Drift – random changes in gene pool over time. There are three important outcomes: 1. Reduces within-population genetic variation 2. More likely to effect small populations 3. Increases between populations genetic variation *Genetic drift reduces genetic variation within a population but increases genetic variation among different populations Genetic drift can result from sampling error (an error that results from a mistake in sampling procedure) Founder effects and population bottlenecks are two forms of genetic drift Founder effects  new subpopulation is only composed of a few original population There are 2 consequences: (movement  migration) 1. Individuals can have reduced genetic variation from the original population 2. Individuals may have a non-random sample of genes in the original population Example: Afrikaners (Dutch colonists) high gene frequency  Huntington’s disease Population bottlenecks  occur when there’s a drastic reduction in a population’s size for at least one generation. Allele frequency can change dramatically as the population size increases after the bottleneck event (example: northern elephant seals. The seals were hunted but then increased in population however this population lacked much variation in their genes.) (Tragedy strikes, such as hunting pressures, which decreases the initial population) Gene Flow  (non-random process) is the movement of individuals, and genes, between populations. Gene flow allows alleles to be reintroduced to a population and this increases the genetic variation within a population. Decreases the genetic variation between populations Reduced gene flow + increased genetic drift = new species Natural Selection and Adaptation  Natural selection acts on existing variation in a population.  Natural selection doesn’t create variations. 4 * = Exam question  Natural selection can increase or decrease variations within and between population Entities = un
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