Bio Anth, Week 4 of Notes
Bio Anth, Week 4 of Notes Anth 1001
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This 7 page Class Notes was uploaded by Jaimee Kidd on Thursday February 4, 2016. The Class Notes belongs to Anth 1001 at George Washington University taught by Shannon C. McFarlin in Spring 2016. Since its upload, it has received 20 views. For similar materials see Biological Anthropology in anthropology, evolution, sphr at George Washington University.
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Date Created: 02/04/16
Cell Division (cont.) Cell Division • Mitosis ◦ Mitosis is cell division in somatic cells ◦ Occurs during growth and repair/replacement of tissues ◦ The result of mitosis is two identical daughter cells, which are genetically identical to the original cell (2 diploid cells) ◦ Several basic events that need to happen before cell division can take place ▪ genetic material replication or duplication ▪ material needs to be separated from its parent copy ◦ Phases: ▪ (1) Interphase ▪ DNA replication happens during interphase right before the rest of cell division is initiated ▪ (2) Prophase ▪ Chromosomes visible with 2 identical sister chromatids (sister chromatids because they are representative of the same chromosome and thus possess the same DNA) ▪ (3) Metaphase ▪ Nucleus disappears ▪ Chromosomes line up single file along equator of cell ▪ one sister chromatid containing one copy of the deny positioned on one side of the equator and the other sister chromatid positioned on the other side ▪ preparing to be pulled apart ultimately ▪ (4) Anaphase ▪ Sister chromatids separate ▪ The two copies of DNA are thus separated ▪ (5) Telophase ▪ Results in two daughter cells (diploid) with identical copies of genetic material (each have their own nucleus, one copy of DNA) • Meiosis ◦ Production of gametes (sex cells) ◦ Characterized by two rounds of division that result in four daughter cells, each of which contains 23 chromosomes (4 haploid cells) in humans ◦ Fertilization restores the full complement of chromosomes (diploid number of 46) to the zygote ◦ Phases: ▪ Characterized by two phases of division ▪ (1) First Division (Reduction) ▪ Interphase DNA Replication ▪ Prophase I Crossing over (genetic recombination) ▪ as chromosomes condense, homologous pairs of chromosomes find each other, this provides an opportunity for crossing over to occur, each member of homologous pairs, come together and cross over exchanging genetic material ▪ after crossing over occurs, the mother chromosome actually traded genetic information with the father’s chromosome ▪ Metaphase I ▪ Chromosomes align in homologous pairs ▪ Random assortment of chromosome members with respect to either side of the equator ▪ Anaphase I ▪ Members of chromosomes pairs separate (Reduction Division) ▪ Telophase I further separation ▪ Interkenesis I ▪ Two haploid daughter cells, which are genetically dissimilar; no DNA replication ▪ Results of Meiosis Division 1 ▪ Each daughter cell inherits half as many chromosomes as the original cell, only one member of each homologous pair (i.e. haploid) ▪ Each chromosome has two chromatids, but they are different because of crossing over ▪ There has been recombination of genetic material from the mother and father ▪ (2) Second Division ▪ Prophase II ▪ No further replication of DNA ▪ Metaphase II ▪ Chromosomes line up single file at the equator (similar to metaphase of mitosis ) ▪ Anaphase II ▪ Telophase II ▪ Daughter Cells ▪ 4 Haploid Gametes, genetically dissimilar ◦ Nondisjunction of Autosomes during Meiosis ▪ One daughter cell receives two copies of the chromosome, and the other daughter receives no copies ▪ In the next phase of Meiosis, these copies with continue to replicate ▪ Usually these nondisjunction events are lethal and the organism does not survive ▪ Non lethal disjunction event ▪ trisomy 21 Downs Syndrome ◦ Mendel’s Laws of Particular Inheritance ▪ Law of Segregation ▪ Paired hereditary factors segregate randomly during formation of gametes ▪ Law of Independent Assortment ▪ Factors controlling for inheritance of different traits assort independently of one another ▪ exception* Applies to genes located on different chromosomes, but genes located on the same chromosome (linkage) may be exceptions ◦ Evolutionary Significance of Meiosis ▪ Meiosis increases genetic variation: ▪ Crossing over (genetic recombination) ▪ Random assortment (genetic recombination) ▪ Mutation (source of new variants) ▪ only mutations occurring during MEIOSIS are heritable ▪ Provides the raw material for natural selection to act upon Genetics II: From Genotype to Phenotype Biological Role of Genetic Material • Accurate Replication • Stable Structure • Capable of coding for diverse information, including proteins • Capable of transmitting this information, to regulate development and normal cell functioning—coordinate the activity of those proteins The Building Blocks of DNA: Nucleotides • Deoxyribonucleic acid (DNA) is a nucleic acid ◦ Resides in the nucleus of the cell ◦ Stores and transmit information ◦ Made up of smaller molecules called nucleotides • Chargaff’s Rule ◦ A=T and G=C • Rosalind Franklin’s Xray diffraction photos provided clues to the structure of DNA showing that DNA was a helical structure DNA: Deoxyribonucleic Acid • Double Helix Structure • Compromised of Nucleotides: ◦ (1) Phosphate ◦ (2) Sugar (deoxyribose) ◦ (3) Nitrogenous base ◦ (Phosphate and sugar form the background) • Located in the nucleus of the cell • Complimentary base pairing: ◦ Adenine = Thymine ◦ Cytosine = Gamine • Implications of DNA Structure: ◦ Complimentary polynucleotide chains (specificity of base pairing) provides a mechanism by which the molecule can replicate itself ▪ one strand forms the template for the creation of the other strand ◦ The sequence of nucleotide bases caries and contains important information (i.e. the genetic code…) • Functions: ◦ Replication (cell division) ◦ Protein Synthesis (genotype to phenotype) • DNA Replication ◦ Occurs during Cell Division ◦ All of this occurs inside the nucleus of the cell ◦ Prior to Cell Division, special enzymes break hydrogen bonds between nucleotide bases resulting in ultimately an unzipping got the molecule somewhere along its length continuing towards both ends of the molecule ◦ Original polynucleotide strands separate, leaving their bases exposed ◦ Original strands become templates for attracting complimentary bases and bond to them to create a new polynucleotide molecule ◦ End result: two identical copies of the DNA molecule Protein Synthesis (from genotype to phenotype) • Genotype= underlying genes • Phenotype= physical outcome • Proteins may serve as structural components of body tissue and play active roles • Amino Acids, Polypeptide Chains and Proteins ◦ Amino Acid subunits are linked together to form linear polypeptide chains ▪ 20 different amino acids ▪ Create an unlimited amount of proteins based on the sequence of the amino acids ◦ Different polypeptide chains can be associated to form complex (multimeric) proteins • The Genetic Code ◦ Information to make proteins is encoded in the nucleotide base sequence ▪ CODON= a sequence of three nucleotide bases, which code for one amino acid ▪ Amino acids are specified by three nucleotide bases ◦ 4 nucleotide bases can combine to produce 64 sequences—coincide with only 20 amino acids ◦ Only 20 amino acids (redundancy). Many amino acids specified by more than on codon sequence ▪ because of this, many mutations still result in functionality ◦ gene: sequence of DNA bases that carries information for synthesizing a particular protein, and occupies a specific chromosomal locus • Protein synthesis takes place outside of the nucleus • DNA needs to be carried outside of the nucleus by ribosomes to begin protein synthesis ▪ Ribonucleic acid RNA ▪ single stranded ▪ ribose sugar ▪ uracil base ▪ DNA ▪ double stranded ▪ deoxyribose sugar ▪ thymine base • Stages (2) ◦ (1) Transcription ▪ Happens inside the nucleius ▪ DNA splits in the region of gene and attracts complementary ribonucleotides to assemble a messenger RNA molecule ▪ Complimentary messenger RNA (mRNA) strand is synthesized. This mRNA will leave the nucleus and travel to the ribosome for protein synthesis ▪ DNA: AAA CGC ▪ mRNA: UUU GCG ◦ (2) Translation: ▪ When the mRNA binds to the ribosome, protein synthesis is initiated. As each codon in the mRNA sequence is “read” a tRNA brings the corresponding amino acid to the ribosome ▪ happens outside the nucleus at the ribosome ▪ Transfer RNA (tRNA) molecules bind the the complementary mRNA strand at the ribosome, bringing with them amino acids specified by the mRNA codon ▪ As amino acids are brought to the ribosome, they bind together to from he amino acid chain of synthesized protein • REVIEW: ◦ DNA: ATA GAT CGC TTA ◦ mRNA: UAU CUA GCG AAU DNA Mutation • = an alternation in the genetic code; source of new variants ◦ Chromosomal Mutations ◦ Point Mutations —> when a single base is incorrectly replication ◦ Duplication —> when multiple strands are replicated incorrectly ◦ Inversion —> when a strand is replicated backwards ◦ Deletions —> when a nucleotide or series of nucleotide gets incorrectly deleted • When mutation occurs at the level of the nucleotide base, it may or may not alter function • Mutations occur at random; they may also be included by other agents • Mutations may be functionally irrelevant; of those that are functionally significant , many are lethal or have negative consequences. Others may be neutral. • A small proportion may be beneficial and confer selective advantages. • If the mutation occurs during meiosis, it may be passed to the next generation. Genetics Beyond Mendel • Mendelian Inheritance: ◦ single gene, autosomal dominantrecessive model ◦ useful for examining traits with qualitative variation (discrete changes) ▪ examples: ppea seed color, ABO blood system, albinism, cystic fibrosis ◦ Codominance ▪ Both alleles in the heterozygous condition are fully expressed, with neither being dominant over the other. ▪ ABO Blood System ◦ Sex Linkage (Xlinked Traits) ▪ Controlled by genes on the X chromosome, more commonly expressed in males. As males (XY) have only one X chromosome, any allele will be expressed, whether dominant or recessive. ▪ Examples of recessive Xlinked traits: Hemophilia, redgreen color blindness • Traits that do not follow Mendel’s rules ◦ Polygenic traits ▪ Traits with quantitative (continuous) variation, influenced by two or more genes ▪ Stature, skin color, eye color ◦ Pleiotropy ▪ A single gene influences the expression of multiple traits simultaneously ▪ Marfan syndrome ◦ Environmental effects ▪ many aspects of the phenotype are influenced by the interaction of genes and the environment ▪ Genotype sets limits and potential for developmental processes • The Complex Genome ◦ Types of Genes ▪ Structural Genes ▪ Regulatory Genes ▪ Homeotic Genes ◦ Introns and exons ▪ Intron region or stretch of region that is not translated into a known protein ▪ Exons opposite ◦ Splice Variation ◦ Nonprotein coding regions ▪ Introns ▪ Pseudogenes ▪ formally functioning genes that have been subsequently rendered as nonfunctional due to a mutation ▪ Primates, especially humans, have a higher proportion of olfactory pseudogenes than other mammals ▪ Variable number tandem repeats & short tandem repeats
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