Reproduction in the Sea

Heredity:

the passing of traits from parents to offspring

Trait: a genetically determined characteristic or condition

Principles of Heredity1. 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.

fissionfrom 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• Gametes 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

• Gametes are produced through 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

Haploid DiploidHoney

bee 16 32

Crayfish 100 200Rabbit 22 44

Watermelon 11 22

Corn 10 20

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?• Meiosis forms gametes with the correct

haploid number of chromosomes.• 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.