Chapter 13.2 Fertilization and meiosis alternate in sexual life cycles By: Brandi Spalten

Chapter 13.2 Vocabulary Somatic cell: any cell other than those involved in gamete formation Karyotype: When images of chromosomes are arranged in pairs starting with the longest chromosomes Homologous chromosomes: (Homologs) the two chromosomes composing a pair that have the same length, centromere position, and straining pattern Sex chromosomes: X and Y chromosome- determine sex Autosome: all other chromosomes except X and Y Diploid cell: Any cell with two chromosome sets (2n) Haploid cell: Single chromosome set (n) Fertilization: union of haploid gametes to produce diploid zygote Zygote: fertilized egg Meiosis: cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication Alternation of generations: Life cycle that includes both diploid and haploid stages Sporophyte: multicellular diploid stage Spores: haploid cells produced from sporophyte Gametophyte: multicellular haploid stage where a haploid spore divide mitotically

Sets of Chromosomes in Human Cells Somatic cells each contain 46 chromosomes By viewing a Karyotype it is shown that there are 2 chromosomes of each 23 type The 2 distinctive chromosomes are X and Y – Human females have (XX) and Human Males have (XY) Only small parts of the X and Y are homologous and most genes carried on X do not have counterparts on the Y They are called sex chromosomes because they determine the sex- while all other chromosomes are called autosomes We inherit 2 sets of 23 chromosomes – a maternal set (set from mother) and a paternal set (set from father) A diploid cell is any cell with two chromosome sets and has a diploid number of chromosomes, abbreviated 2n=46 Cells with a single chromosome set are haploid cells, abbreviated n=23 – the set of 23 consists of 22 autosomes plus a single sex chromosome http://www.dnatube.com/video/835/Chromosomes-in-Haploid-and-Diploid- Cells

Chromosome set and life cycle Human life cycle begins when a haploid sperm fertilizes a haploid egg, now known as a diploid zygote Meiosis reduces the number of sets of chromosomes from 2 to 1 in the gametes, counterbalancing the double that occurs at fertilization There are 3 main types of sexual life style cycles

Humans and Animals life cycle Gametes are the only haploid cells Meiosis occurs in germ cell during production of gametes, which undergo no further cell division prior to fertilization After fertilization, diploid zygote divides by mitosis producing an organism that’s diploid

Plants and some algae life cycle Alternation of generation includes a diploid stage called sporophyte that produces haploid cells called spores, and a haploid stage called gametophyte Cells of gametophyte give rise to gametes by mitosis The diploid zygote develops into the next sporophyte generation then this generation produces a gametophyte as its offspring, and the cycle repeats

Most Fungi and some protists life cycle After gametes fuse and form a diploid zygote, meiosis occurs without a multicellular diploid offspring developing Meiosis produces haploid cells instead of gametes, that then divide by mitosis and give rise to either unicellular descendants or a haploid multicellular adult organism Only diploid stage found in these species is the single celled zygote

Test Questions Thinking of a plants sexual life cycle, what describes the process that leads directly to the formation of gametes? Gametophyte 2)How are chromosomes arranged in Karyotypes? Starting with the longest chromosomes 3) What are the 3 different types of life cycles? * Animals, Plants and some algae, and most fungi and some protists

Meiosis (Mr. Anderson) http://www.youtube.com/watch?v=rB_8dTuh73c