Principles of Evolution
January 28
Genetics Terms
- Somatic cells - most cells in body, except sex cells
- Gametes - sex cells
- Cytoplasm - mix of membranes, molecules, and organelles
- Nucleus - contains hereditary material, or chromosomes
- Chromosomes - Structures in nucleus containing genes that transmit traits through generations
- (humans have 23 pairs, other animals have more)
Critical Acids (DNA & RNA) Structure
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Deoxyribonucleic Acid (DNA) - nucleic acid used to store genetic information
- Four bases: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T)
- T bonds with A, G bonds with C
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Ribonucleic Acid Molecules (RNA)
- Dictate synthesis of proteins that perform a wide variety of functions in body
- Regulate expression of other genes
- Work with structures in cell (ribosomes) that are critical for manufacture of proteins
- Transport amino acids to ribosomes for the creation of proteins
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Proteins: linear sequence of amino acids (building blocks of cells)
- Function determined by DNA; for example, enzymes (catalysis of biochemical reactions) or hemoglobin (transports oxygen in the blood)
- Many animals (like dogs) cannot process caffeine or chocolate, as they lack the necessary enzymes
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Transcription - synthesis of single strand of mRNA (messenger RNA); results in genetic information transferred from DNA to RNA, then carried to cytoplasm
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Codons - sequence of 3 nucleotides (basic structure unit for DNA/RNA) containing genetic info
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4 nucleotides of RNA are: adenine (A), guanine (G), cytosine (C), and uracil (U) [which replaces thymine (T) in DNA template (uracil replaces thymine for increased RNA stability and replication efficiency)]
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Translation - tRNA (transfer RNA) (information adapter molecule) decodes information in mRNA; amino acid attaches to acceptor stem, then anticodon reads information via base pairing
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DNA -> (Transcription) -> RNA -> (Translation) -> Protein
Genetics and Heredity
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Gene - chemical unit of heredity
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Alleles - one member of a pair of genes
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==Phenotype== - observable physical appearance of organism
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Genotype - total complement of inherited traits or genes
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==Homozygous== - possessing two identical genes or alleles in corresponding locations on a pair of chromosomes. For example, YY or yy
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**==Heterozygous== ** - possessing different genes or alleles in corresponding locations on a pair of chromosomes. For example: Yy
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Dominant alleles - allele of gene pair that is always phenotypically expressed in heterozygous form [For example: Y always expressed phenotypically when paired with y (Yy)]
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Recessive alleles - allele phenotypically suppressed in heterozygous form and expressed only in homozygous form. [For example: y only expressed phenotypically when paired with y (yy)]
In Mendel’s experiment (3 yellow: 1 green phenotypically) (1 YY: 2 Yy: 1 yy genotypically)
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Mutation - randomly occurring; result of error/change in nucleotide sequence; somatic vs germ cell mutations
- Can be neutral, harmful, or (very rarely) beneficial; ultimate source of new genetic materials
- 4 factors: ① copying errors in cell division, ② exposure to radiation (especially sunlight), ③ exposure to mutagens, or ④ exposure to viruses
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Genetic Drift - random changes in gene pool over time
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3 important outcomes: ① reduces within-population genetic variation, ② more likely to effect small populations, ③ increase between-population genetic variation
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Gene Flow - movement of genes between populations
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2 important outcomes: ① initially, increases within-population genetic variation, ② eventually, reduces between-population genetic variation
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Natural Selection - any consistent difference in fitness among phenotypically different biological entities; deterministic process; acts only on existing variation [Deterministic for evolution]
- ==Biological evolution can occur without natural selection, and vice versa==
Adaptation: process and feature
- Process: change in organism enabling it to better reproduce and survive in its environment
- Feature: characteristic that performs a function of utility to the organism possessing it
- Antimicrobial Resistance (AMR) - serious threat to global public health; 480 000 people develop drug-resistant TB each year
- Macroevolution - large-scale changes at or above the species level; extends over geological era
Cladistics: a biological taxonomy sytem
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Based on qualitative analysis of comparative data that is used to reconstruct (assumed) phylogenetic relationships and evolutionary history of groups of organisms
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Clade - a group of organisms that contains an ancestral taxon (group of one/more organism) and all of its descendants; can orient cladogram in any direction with no change
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Tree topology - the branching patterns of lines connecting nodes and organisms
- Focus on internal branches; watch out for polytomies
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Cladogram - branching diagram used to illustrate phylogenetic relationships
- May have any number of clades
- Reading a Cladogram - Interested in tree topology;
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3 Major Assumptions of cladistics
- There are changes in characteristics within lineages over time (Some have not changed in many years, like Greenland sharks or coelacanths)
- All organisms are descended from a common ancestor
- When a lineage splits, it divides into exactly two groups
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How to do Cladistics:
- Choose taxa whose evolutionary relationships interest you. These taxa must be clades (monophyletic group) if you hope to come up with plausible results
- Determine characters (features of organisms) and examine each taxon to determine character states (decide whether each taxon does or does not have each character)
- Determine polarity of characters (character state is original or derived in each taxon) using out-group (more distantly related group of organisms that serves as a reference group)
- Group taxa by synapomorphies (shared derived characteristics; derived) not symplesiomorphies (original, or “primitive”, characteristics; ancestral)
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3 Misconceptions About Cladograms
- Evolution produces patterns of relationships among organisms that are like a tree
- Although cladograms are often organized from top to bottom, don’t assume the taxa on top are more advanced than those taxa on the bottom
- Avoid reading across terminal nodes (tips), order of which has no meaning