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

2. 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

3. 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
Cells

5. 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

6. 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

7. 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

8. 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

9. 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

10. Meiosis (Mr. Anderson)