Bio; Lecture 13; Animal Evolution

Bio; Lecture 13; Animal Evolution - Principles of Biology 2...

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Principles of Biology 2 BIO U103 2/8/07 Animals are classified into different taxanomic groups depending on: o Physical characteristics organism shows o Embryo development o Body symmetry o Architectural evolutionary innovation Embryology Embryology is the understanding of how the zygote develops Zygote: fertilized egg (diploid cell) Also need to understand how we use differences in development to classify organisms Sperm provides a copy of DNA for the egg Sperm: o Only the head of the sperm (which contains DNA—not mitochondria) moves into the egg o Mitochondria do not move into the egg, therefore, mitochondria is a maternal trait (comes from the mother) o Sperm is energetically cheap to produce Eggs are large and expensive to produce o Contain a lot of cytoplasm and nutrients o Women are born with a set number of egg Preformation: idea that the egg or sperm contains an embryo that is a pre-formed miniature adult o This idea is false however Stages of embryology o Zygote: fertilized egg o Cleavage: zygote separates into two cells, then into four o Morula: 16-64 cells o Blastula: 128 cells o Gastula Polyspermy o Many sperm attach themselves to the egg o Only one enters however o Once first sperm enters, the egg produces a fertilization membrane instantly, and doesn’t allow more sperm from getting in o This avoids polyspermy Fertilization process o Sperm activates the egg and brings together both of their nuclei o The head of a sperm cell contains enzymes o These are released onto the cell membrane of the egg o The sperm then buds through the membrane, and the head enters, leaving the rest beind. o Fertilization membrane starts forming right after this process occurs o This happens in order to avoid polyspermy—trisomy - 1 -
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Principles of Biology 2 BIO U103 2/8/07 o It is important to do this because extra copies of chromosomes can be very costly Concept of Epingenesis: o states that the form of a animal emerges from a relatively formless egg o an organism’ development is primarily determined by the genome of the zygote and the organization of the egg cytoplasm
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This note was uploaded on 05/26/2008 for the course BIO 103 taught by Professor Potts-santone during the Spring '07 term at Northeastern.

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Bio; Lecture 13; Animal Evolution - Principles of Biology 2...

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