Meiosis The ability to pass on traits is called heredity. – This ability is one of the unifying themes of biology as individual units of heredity (genes) are passed from one generation to the next in reproductive cells called gametes. – Organisms can reproduce in 2 basic ways; sexually and asexually.

Sexual Reproduction gametes from 2 different parents, created during meiosis, blend genes to create variation within the species – gametes are produced via meiosis and each have 1/2 the DNA of the somatic cells from which they were derived

Asexual Reproduction offspring reproduced via mitosis – each offspring is a clone of the parent – examples range from budding (hydra) and binary fission (bacteria) where offspring separate and grow to plants, algae, and fungi that have offspring with 1/2 DNA of the parent

Reproductive Cycle Humans In the human reproductive cycle the somatic cell carries 46 chromosomes: 22 pairs of autosomes & 2 sex chromosomes. – The somatic cell is said to be diploid (2n = 46) where each cell retains 2 copies of each piece of DNA gametes are said to be haploid (n = 23) having only one copy of each. – Each pair (excluding sex cells) is said to be homologous share a similar centromere region, gene locus, and staining pattern when condensed. The display of the homologous chromosomes when condensed is the organisms karyotype. – haploid cells are produced in the testis and ovaries (n = 3) via meiosis – cells are joined via fertilization to form a zygote and are now diploid (2n = 46) – mitosis and cell differentiation form an individual with similar traits to the parents

Alternate forms of reproduction Plants & some algae – alterations of generation - both diploid and haploid are multicellular diploid is the sporophyte stage – meiosis produces spores spores grow into an organism called a gametophyte through mitotic division of the haploid cell – gametophyte make gametes via mitosis which fuse to form a diploid zygote diploid organism grows into a sporophyte

Alternate forms of reproduction Most fungi and some protists – haploid multicellular organism – fertilization forms a diploid zygote that immediately undergoes meiosis to produce haploid adults