11.4 Meiosis Chromosome Number P323 Q: How many sets of genes are found in most adult organisms? A: 2 complete sets of inherited chromosomes & 2 complete sets of genes.

Humans have 23 pairs or 46 chromosomes .

Diploid Cells Homologous-chromosomes that each have a corresponding chromosome from the opposite-sex parent Diploid- two sets-2N Haploid-one set-N

Meiosis-Reduction Division Only with Gametes-(sex cells) Meiosis I and Meiosis II (PMAT 2 times)

Prophase I-each replicated chrom Prophase I-each replicated chrom. pairs with its corresponding homologous chrom. Tetrad- is formed (4 chromatids) Crossing-over-exchange of alleles between homologous chromosomes and produces a new combination of alleles.

Metaphase I Line up across middle.

Anaphase I Pulled to opposite ends of the cell

Telophase I Nuclear envelope forms Cytokinesis occurs

Meiosis II Prophase II-Chromosomes visible

Metaphase II Line up middle

Anaphase II Move to ends

Telophase II Nuclear envelope forms Cytokinesis divides End up with 4 genetically different cells.

Zygote-fertilized egg.

Comparing Mitosis and Meiosis

Mitosis Meiosis General cells Genetically identical No crossing over No pairing of homologous chrom. 1 division result 2 cells Chrom. # remains same Only sex cells (gametes) Genetically different. Crossing over Yes pairing of homologous chrom. 2 divisions result 4 cells Chrom. # reduced by ½

Gene Linkage Q: How can 2 alleles from different genes be inherited together? A: Alleles of different genes tend to be inherited together from 1 generation to the next when those genes are located on the same chromosome.

P171-175 skip #28, 29, 30, 32, 33, 34, 39 p176 extra credit Study for vocab quiz tomorrow.