Chromosomes & Inheritance Gene Segregation during MEIOSIS 3 significant results 1. Haploid cells because of 2 divisions following only 1 DNA replication. Fusion of haploid nuclei (sexual reproduction) restores the diploid number 2. Metaphase 1- maternal & paternal chromosomes have equal chances of aligning on the equator, resulting in combinations of chromosomes from both parents

Chromosomes & Inheritance Gene Segregation during MEIOSIS 2. Number of possible chromosome combinations in haploid nuclei from meiosis is LARGE (greater with more chromosomes)! Formula for possible chromosomal combinations in the resulting nuclei is 2 n (n=number of chromosome pairs) 3. Crossing-over generates more variation. It occurs every meiosis and sites vary every meiosis.

Chromosomes & Inheritance MEIOSIS in Animals & Plants ANIMALS Made of mostly diploid cells Meiosis produces haploid gametes Fusion of haploid gametes produces a diploid zygote during fertilization, which then carries out mitosis (sexual reproduction) Gametes are the only haploid stage of the life cycle (formed in specialized cells) Males – spermatogenesis (production of spermatozoa - sperm) takes place in the testes;

Chromosomes & Inheritance MEIOSIS in Animals & Plants Females – oogenesis (creation of an ovum – egg cell) takes place in the ovaries Males – spermatogenesis (production of spermatozoa - sperm) takes place in the testes;

Chromosomes & Inheritance MEIOSIS in Animals & Plants Sexually reproducing plants have 2 phases 1.Gametophyte (haploid) – gametes are produced PLANTS 2. Sporophyte (diploid) – haploid spores are produced Angiosperm (flowering plants) Flower is where sexual reproduction takes place

Chromosomes & Inheritance MEIOSIS in Animals & Plants Female reproductive organs: Pistils – stigma, style, ovary Stigma – sticky surface to collect pollen Style – thin stalk down which the pollen tube grows from the stuck pollen Ovary – contains ovules (embryo sac with a single egg cell)

Chromosomes & Inheritance MEIOSIS in Animals & Plants Male reproductive organs: Stamen – anther, filament Anther – release the pollen Filament – the stalk

Chromosomes & Inheritance MEIOSIS in Animals & Plants Plants produce gametes from “gametophytes” Plants life cycles include 2 phases called the alternation of generations 1.Haploid gametophyte generation Begins with spores produced during meiosis In flowering plants the spores become pollen and embryo sac

Chromosomes & Inheritance MEIOSIS in Animals & Plants 2. Diploid Sporophyte generation Initiated by fertilization Specialized haploid cells (spores) produced

Chromosomes & Inheritance MEIOSIS in Animals & Plants PLANTS Gymnosperm Do not place their seeds in an ovary (fruit) Ex. conifers