 Study for your Keystone Vocabulary Quiz  Turn in packet: Basis of Cellular Inheritance

 Homologous chromosomes: pairs of chromosomes with genes for the same traits, but they can have different information about those traits  ½ the chromosomes in a cell come from Mom, ½ the chromosomes in a cell come from Dad

 Humans have 46 chromosomes or 23 pairs of homologous chromosomes.  Somatic (body) cells contain 46 chromosomes.  46 is the diploid (2N) number for humans. -Diploid means that a cell has both homologs for each chromosome  Somatic cells reproduce by mitosis

 Gametes(eggs (Ovum) and sperm) are called haploid (N) because they contain one set of chromosomes or 23 chromosomes.  Eggs and sperm are produced by meiosis- a process that reduces chromosomes by half  Fertilization is when the haploid nucleus of the father’s sperm fuses with the haploid nucleus of the mother’s egg. ◦ The resulting fertilized egg is known as a zygote is diploid

 Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosome in a diploid cell.  Two steps ◦ Meiosis I and Meiosis II  One diploid cell gives rise to 4 haploid cells

 Plants  Fungi  Animals (including you) ◦ Males start meiosis at puberty. ◦ Females start meiosis in utero.

 In your gonads ◦ Females- the ovary ◦ Males-the testicles

 Genetic Variation ◦ Mixes genes from Mom and Dad to create a unique baby  Reduce the chromosome number by half  Ensures that each cell produced has one copy from each homologous pair of chromosomes  23 in sperm + 23 in egg unite (fertilization) leads to a 46 zygote(baby)

 Prior to this phase, each chromosome is replicated ◦ Then its looks a lot like Mitosis with 4 phases  Prophase I  Metaphase I  Anaphase I  Telophase I and Cytokinesis  The major difference is what happens in Prophase I

 Homologous chromosomes join to form a tetrad  Chromosomes in the tetrad exchange portions of themselves in process known as crossing-over

 Results in new genetic combinations - It is another way to increase genetic diversity

 The rest of Meiosis I looks the same as Mitosis except ◦ The two new cells have sets of chromosomes and alleles that are different from each other and from the diploid cell that enter meiosis I

 This time no chromosome replication occurs before entering prophase II. ◦ Again it looks similar to Mitosis but now we have a separation of the chromosomes  Resulting in four new cells with half number of chromosomes (haploid cells)

 Mitosis results in the production of two genetically identical diploid cells. ◦ Allows an organism to grow, reproduce, and replace cells.  Meiosis results in the production of four genetically different haploid cells. ◦ Allows organisms to reproduce sexually

Crossing-Over

Define/Add these words on back: - Homologous Chromosome - Crossing Over * Sister chromatids are exact replicas but homologous chromosomes are not! Same genes with different Version of that gene CROSSING OVER