Chapter 12 Lecture Outline

Chapter 12 Lecture Outline - Biology 100 Vandan Desai...

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Biology 100 Vandan Desai Chapter 12: Meiosis (Lecture Outline) -------------------------------------------------------------------------------------------------------------------------- Ultimate explanation evolutionary in nature; explains why something happens Proximate explanation mechanistic in nature; explains how something happens During sexual reproduction , a male reproductive cell—a sperm —and a female reproductive cell—an egg —unite to form a new individual o The process of uniting sperm and egg is called fertilization Meiosis: o Nuclear division that leads to a halving of chromosome number o It precedes the formation of eggs and sperm , and provides a satisfying proximate explanation for how sexual reproduction occurs I. How Does Meiosis Occur? A. A pair of chromosomes that have same size, shape, and content are homologous chromosomes (homologs ) i. Carry the same genes —section of DNA that influences one or more hereditary traits in an individual ii. They may a different allele —different versions of a particular gene B. Sex chromosomes —pair of chromosomes carrying the gene(s) that determine sex C. Autosomes —pair of chromosomes that do not carry the gene(s) that determine gender D. Karyotype —number and types of chromosomes present E. Diploid —organisms that have two versions of each type of chromosome F. Haploid —cells contain just one of each type of chromosome i. Do not contain homologous chromosomes ii. Just have one allele of each gene G. Haploid number ( n )—number of distinct types of chromosomes in a given cell H. Ploidy —number of each type of chromosomes present (For example—1 n , 2 n , 3 n ) i. Diploid organisms/species designated 2 n b/c two chromosomes of each type are present— one from each parent ii. Haploid organisms/species labeled n b/c they have just one set of chromosomes— no homologs are observed I. An Overview of Meiosis i. Cells replicate each of their chromosomes before undergoing meiosis ii. After replication, each chromosome consists of two identical sister chromatids iii. Sister chromatids are joined at a portion of the chromosome called the centromere and along their entire length iv. Meiosis consists of two cell divisions, called meiosis I and meiosis II a. Meiosis I: Homologs in each chromosome pair separate from each other The two homologs go to two different daughter cells Each daughter cell ( haploid = n ) contains half as many chromosomes as the parent cell ( diploid = 2 n ) has b. Meiosis II: Sister chromatids from each chromosome separate The two sister chromatids go to two different daughter cells
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Biology 100 Vandan Desai Each daughter cell has one of each type of chromosome, but now the chromosomes are unreplicated v. Outcome of meiosis is
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Chapter 12 Lecture Outline - Biology 100 Vandan Desai...

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