Reproduction in the Sea

Heredity : the passing of traits from parents to offspring Trait Trait : a genetically determined characteristic or condition

Principles of Heredity 1. Traits are controlled by alleles on chromosomes. 2. An allele’s effect is dominant or recessive. 3. When a pair of chromosomes separates during meiosis the different alleles for a trait move into separate sex cells.

Cell Division

Asexual Reproduction In asexual reproductions, one parent organism produces offspring through mitotic cell division Unicellular organisms often use this method Because the offspring inherit all their DNA from one parent, they are genetically identical to each other and to their parent. Disadvantage: provides very little genetic variety

Forms of Asexual Reproduction Fission/Mitotic cell division Fragmentation Budding Regeneration Spore Cloning Vegetative reproduction

Fission Cell division in prokaryotes is known as fission. A prokaryote’s DNA molecule is copied and each copy attaches to the cell membrane. The cell grows longer, pulling the two copies of DNA apart while the cell membrane begins to pinch inward along the middle of the cell. fission from Latin fissionem, means “a breaking up, cleaving”

Example: Bacteria Through fission, the cell splits and forms two new identical offspring.

Mitotic Cell Division In mitotic cell division, a unicellular parent cell becomes two identical offspring. The parent cell no longer exists. Example: Amoeba

Disadvantages of Asexual Reproduction One disadvantage of asexual reproduction is that the results offer little genetic variation within the population. Asexual reproduction can also be responsible for harmful genetic mutations.

Advantages of Asexual Reproduction One advantage of asexual reproduction is that it allows organisms to reproduce without a mate, saving time and energy. Asexual reproduction also enables some organisms to produce large numbers of offspring in a short period of time.

Sexual Reproduction A type of reproduction in which the genetic materials from two different cells combine, producing an offspring. Two organisms give a complete copy of their genes to form a new organism

Gametes GametesGametes are special reproductive cells designed to transfer or receive chromosomes. These cells have only one, not two of each kind of chromosome found in an organism. –Human cells have 46 chromosomes –Human gametes have 23 chromosomes meiosisGametes are produced throu gh meiosis.

Haploid Cells Haploid cells are cells that have only one chromosome from each pair of chromosomes.

Diploid Cells Diploid cells are cells that have pairs of chromosomes. Pairs of chromosomes that have genes for the same traits arranged in the same order are called homologous chromosomes. Because one chromosome is inherited from each parent, the chromosomes are not identical. Different organisms have different numbers of chromosomes.

Haploid vs. Diploid

HaploidDiploid Honey bee 1632 Crayfish Rabbit2244 Waterme lon 1122 Corn1020

Meiosis meiosis In meiosis, one diploid cell divides and makes four haploid sex cells. Meiosis occurs only during the formation of gametes.

Meiosis I

Meiosis II

Why is Meiosis Important? correct Meiosis forms gametes with the correct haploid number of chromosomes. genetic variation Meiosis also creates genetic variation by producing haploid cells. When haploid gametes join together during fertilization, they make a diploid zygote, or fertilized egg.

Why is Meiosis Important? The fertilized egg, formed when sex cells join together, divides by mitosis to create a diploid organism.