Asexual vs. Sexual Reproduction

Asexual Reproduction

• A form of reproduction which does not involve meiosis or fertilization.

• Involves one parent. • The primary form of reproduction for

single-celled organisms such as archaea, bacteria, and protists.

• Many plants and fungi reproduce mostly asexually as well.

Binary Fission

• Cell splits and replicated DNA goes with each part

• Prokaryotes, Bacteria

Bacterial Conjugation

• A bacteria shoots out a tube and sends a piece of its DNA to another bacteria

• Bacteria

Fragmentation/Regeneration• Body of parent

breaks and produces offspring

• Fungi, moss, sea stars, planarian

Budding

• Offspring grows out of parent

• Yeast, hydras

Sexual Reproduction

• Results in increasing genetic diversity of the offspring.

• Characterized by two processes:– meiosis, halving of the number of

chromosomes– fertilization, combination of two gametes and

the restoration of the original number of chromosomes

• During meiosis, chromosomes usually cross over = genetic recombination.

• Primary method of reproduction for the vast majority of visible organisms, including almost all animals and plants.

Pollination• Pollen is

delivered to female part of plant

• Flowering plants

Sexual Reproduction

• DNA from 2 individuals merge to form one

• Animals, Plants

Mechanisms ofSexual Reproduction

External Fertilization

• Getting gametes together– Eggs are shed by the female and

fertilized by the male– Requires an environment where an egg

can develop without desiccation or heat stress occurs almost exclusively in moist habitats

– Most fishes and amphibians

Internal Fertilization

• Getting gametes together– Occurs when the sperm are deposited in

(or nearby) the female reproductive tract; egg and sperm unite within the female’s body

– Requires cooperative behavior that makes copulation possible, as well as sophisticated reproductive systems

Protection of the Embryo

• External Fertilization– Enormous numbers of zygotes produced; only

a few survive

• Internal Fertilization– Produces fewer zygotes wherein more survive

• Resistant eggs, development of embryo within the reproductive tract of female parent, parental protection of eggs