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Bio%20201%20S12%20Lect%205%20%28True%29%20v3r -...

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Biology in the News (see folder on BB) Mul6ple 6mes in evolu6on, mul6cellular organisms have evolved from single celled species in which individuals evolved the ability to s6ck together and cooperate as a single en6ty Scien6sts have now recapitulated this phenomenon in the laboratory using Brewer's yeast, Saccharomyces cerevisiae , a single celled organism The yeast were grown in a rich liquid culture and each day, the culture was centrifuged gently to separate the contents of the culture by weight cell clusters moved to the boCom during centrifuga6on because they are heavier the boCom frac6on of the post‐ centrifuga6on culture was then agitated to break up the clusters and used to start a new genera6on of liquid culture this was done for ±0 genera6ons the surviving strains grew as clusters, not as single cells cells in the same cluster were more related to each other than cells in diFerent clusters, indica6ng that the clusters formed during growth also, when clusters reached a certain size, some cells died, which is thought to be due to apoptosis or "programmed cell death", a characteris6c of mul6cellular organisms since this was so easy to achieve in lab, one of the big remaining ques6ons is why it didn't evolve more oJen in the tree of life (mul6cellularity is es6mated to have evolved about 25 6mes in the history of life on Earth) hCp://www.nsf.gov/news/news_summ.jsp? cntn_id=122828&WT.mc_id=USNS²_51&WT. mc_ev=click
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a brief review Diploid and haploid Mitosis: diploid parental cell duplicates its DNA (chromosome(s)) and divides once to yield two iden6cal daughter cells Haploid cells can also duplicate via mitosis Meiosis: diploid parental cell duplicates its DNA (chromosome(s)) and then goes through two divisions to yield four non‐iden6cal haploid progeny cells (gametes)
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Bio%20201%20S12%20Lect%205%20%28True%29%20v3r -...

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