Intro Genetics and Meiosis Chapter 13

Vocabulary parental generation filial generation heterozygous heredity variation gene gamete somatic cell asexual vs sexual reproduction autosomes sex chromosomes allele dominant vs recessive diploid vs haploid parental generation filial generation heterozygous homozygous phenotype genotype sex-linked gene Locus Trait true-breeding hybrid

Where does genetic diversity come from? original source is mutations (mistakes in DNA) that result in different alleles sexual reproduction causes reshuffling of the alleles to produce a population with a unique combination of traits

Chromosome Anatomy Revisited Humans = 46 chromosomes (23 pairs) for analysis, chromosomes organized into karyotypes homologous chromosomes (pairs), each contain genes controlling the same inherited characteristics one chromosome is inherited from each parent (dominant allele is expressed--usually)

Meiosis cell division in sperm and egg cells (produces haploid cells) In humans, 23 chromosomes two cells unite during fertilization to produce diploid cell (zygote) In humans, 46 chromosomes goal to ensure genetic diversity in sexually reproducing organisms

Meiosis I (separates homologous chromosomes) (figure 13.8) Meiosis I (separates homologous chromosomes) crossing over occurs during prophase I otherwise identical steps to mitosis (non-identical haploid cells produced) Meiosis II (separates sister chromatids) identical steps to mitosis (produces non-identical haploid cells)

Gametogenesis Production of gametes (sperm/egg cells) Within the testes/ovaries precursor cells (spermatocytes and oocytes) exist in the diploid form These precursor cells then go through meiosis to form haploid sperm/egg cells which are used in sexual reproduction to produce offspring Spermatogenesis Oogenesis

Meiosis…again. Reduction Division (creates haploid cells) Meiosis I Two HAPLOID cells produced Chromosomes have crossed over Meiosis II Four HAPLOID cells produced Genetically unique cells Ensures genetic diversity of a species through… Independent assortment of homologous chromosomes Crossing over of homologous chromosomes

Independent Assortment During Meiosis I, maternal and paternal chromosomes align randomly on metaphase plate (daughter cell has 50/50 chance of getting either) each pair of chromosomes is sorted independently from one another (daughter cells will have various combinations of chromosomes from mom/dad) In humans there are over 8 million different combinations with 23 chromosomes from two parents (223)

Crossing Over occurs during prophase I two non-sister chromatids (tetrad) trade alleles thus combining genetic information from two parents Chiasma: site of crossing over results in genetic recombination (offspring with different combination of traits than parents) Coupled with independent assortment, this results in over 23 trillion different combinations from both parents You are 1 in 23 trillion! recombinant chromosomes: individual chromosomes that carry genes derived from two different parents 1-3 cross-over events per pair of chromosomes at most

Mr. Knuffke Meiosis Prezi Link Awesome meiosis square dancing video! https://prezi.com/el-sh-qgrgsj/ap-bio-information-7-meiosis/

Mitosis vs. Meiosis (figure 13.9)