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LS15 - Week 2 & 3

by: AK315

LS15 - Week 2 & 3 Life Science 15

GPA 3.8

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Notes for Week 2 & 3 of the course
Life: Concepts and Issues
Professor Phelan
Class Notes
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This 5 page Class Notes was uploaded by AK315 on Thursday March 10, 2016. The Class Notes belongs to Life Science 15 at University of California - Los Angeles taught by Professor Phelan in Winter 2016. Since its upload, it has received 23 views. For similar materials see Life: Concepts and Issues in Biology at University of California - Los Angeles.


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Date Created: 03/10/16
Week 2 & 3 Darwin’s Ideas He wrote the 1859: Origin of species (which was his work that was published - check out the last paragraph !) A trait can change over time within a species if there is: 1. Variation for a trait (Darwin observed this) 2. Heritability (Darwin couldn’t quite explain this which is where Mendel came in) 3. Differential reproductive success Gregor Mendel He was a monk and he experimented with peas to study heritability. Often credited as the father of ‘genetics’. Mendel gave a talk in 1965 on the “Inheritance in Pea plants”. However, the ordinary people could not wrap their head around his way of thinking and eventually he came to believe that he didn’t figure it out. Only 35 years later scientists understood that Mendel figured it out. Generic Cell • A chromosome is a linear strand. Humans have 23 unique chromosomes. We have 2 copies of each chromosomes (a pair). They number the chromosomes by size. • Under the microscope, the chromosomes look like X’s (but we can try to visualize them as spaghetti strands). • The chromosome looks like an X because essentially it’s a chromosome + a copy of itself coiled up and connected. • Humans have 23 homologous pairs. • Karyotype - a picture of all chromosomes in a cell. • You might want to look at a karyotype to determine based on the chromosomes if babies develop problems. • For instance having an extra copy of a chromosome which is trisome 21 (3 copies of chromosome 21) leads to down’s syndrome. • Both the maternal and paternal copy of the chromosomes contain many genes each (many instruction sets to produce a particular trait). Mendel’s Laws Law of Segregation • A gamete receives only 1 allele for each gene (Even though the organism general has 2). • Fertilization re-establishes the diploid number. A diploid (contains 2 of each allele) and a haploid (contains only 1 of each allele) • Albino organisms have 2 copies of the pigment gene that doesn’t produce any pigment. Use a punnet square for assessing the cross. For mM x Mm case: Genotype ratio is 1:2:1 Phenotype ratio is 3:1 (pigmented:albino) assuming that M was the dominant gene and ‘m’ (albino pigment gene) was the recessive one. The law of segregation points out that a gamete receives only one copy of each gene from both parents. Law of Independent Assortment The allele you pass on for one trait has no effect on which allele you pass on for some other trait If an individual shows the dominant phenotype, how can you determine their genotype? We see a dominant trait phenotype > B__ = BB or Bb What cross would help? X homozygous recessive gene The test cross allows you to determine whether individuals showing the dominant trait are homozygous or heterozygous. Sex determination How is the sex of a baby determined by the father? Girl vs Boy XX (maternal) vs X (maternal) & Y (paternal) So sperm can carry either X or Y chromosome whereas females always contribute an X chromosome. Methods of sex determination: • Male heterogamety • Female heterogamety (honey bees can control the sex of their offspring - if they fertilize their eggs with sperm then female but if the choose not to fertilize their eggs then the unfertilized eggs go on to become males) • Ploidy • Incubation temperature If men only have one X chromosome, are they more or less likely to exhibit a sex-linked recessive trait? What about dominant?   White eyed female (Xr Xr) vs Red-eyed male (XR vs Y) females = Xr x XR = Red eyes (dominant) males = Xr x Y = White eyes (Recessive) Sex linked traits have different patterns of expression in males and females Trade off between survival and reproduction Australian mother spider gives birth to many spiders that proceed to suck her dry. It is necessary to ensure offspring live but the spider does not survive. Theory of Kindness Kindness leads to: 1. Shared Genes 2. Reciprocity Why are people nice to other people? 1. Because allele X in you causes you to act in such a way that you increase the reproductive success of other individuals that carry Allele X (Shared genes/Kin selection). 2. Because allele Y in you causes you to help other people who will return the favor, thereby benefitting allele y (Allele Y buffers itself from an uncertain future by storing goodwill in others. 2 ways in which an Allele can increase the market share: 1. Direct fitness (increase the number of offspring I produce) 2. Indirect fitness (increase the number of offspring my kin have; they also carry many of my alleles). If I paid my sister and she was able to take care of herself and have more kids, then because she shares the same alleles from my parents - it would increase the number of offspring my kin has. Inclusive fitness = direct fitness + indirect fitness Hamilton’s Rule How much do we expect individuals to help various relatives? (Hamilton’s rule) equation: B*r > C B - benefit to relatives r - coefficient of relatedness (the probability that an allele that you carry is carried within this individual because of a common ancestor - measured from 0.0-1.0). C - Cost to me (the decrease in my own reproductive output based on my actions) For situations in which this equation is true, we expect the ‘kind’ act to occur. Belding’s ground squirrels: 1. Yell when a predator approaches (sometimes) 2. Hide when they hear a yell (always) 3. 10% of predator attacks end with a dead squirrel 4. 50% of the dead squirrels were the ones yelling Which squirrels are making alarm calls? Adult females (they have tons of relatives - parents, sisters). (male squirrels relocate to a different community at maturity. Females don’t) The more kin a squirrel is likely to have nearby, the more it will act ‘altruistically’.  Hamilton’s rule helps us to predict when we will see ‘kindness’ (When something that benefits someone else comes at a cost to you) ‘r’ is a measure of the proportion of our genes we have in common with our relatives. Rules for calculating ‘r’; 1. UP UP UP and DOWN DOWN DOWN - Never reverse the directions on the path from one individual to another 2. All paths are created equal - dont forget a path. 3. Multiply within and add between paths. example; from parent to offspring r = 0.5 example ; from sibling to sibling r = (0.5*0.5) + (0.5*0.5) = 0.5 (we add the paths from BOTH parents) example; from sibling to half sibling r = (0.5*0.5) = 0.25 example; from cousin to cousin r= 0.125 Altruism requires kin recognition - spatial association (treat those around you as main) - social association (treat those from childhood as kin) - phenotype matching (treat those who resemble you as kin) SUPPOSE you capture an old female ground squirrel and move her to a new neighborhood far away, will they make alarm calls. THE CORRECT ANSWER IS YES. It’s a mistake and what biologists call maladaptive behavior because this squirrel is risking her life and the other squirrels aren’t even her relatives ! This is built in natural selection. What can you conclude? We call it maladaptive behavior because this is an event that hasn’t occurred in her evolutionary history and she’s not yet adapted to it. Behavioral rules of thumb Predictions of Kin Selection: IN MURDER CASES: - Spouses and non-relatives had the GREATEST risk of homicide as opposed to off- spring and parents IN INFANTICIDE CASES: - Children in step-families inured or killed more frequently than those living with their biological parents IN BEQUESTS (WILL/LEAVING INHERITANCE): - individuals will leave more of their estate to close kin than distant kin


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