module1-4

• Animal reproduction is necessary for the survival of a species.
• Asexual reproduction produces genetically identical organisms (clones), whereas in sexual reproduction, the genetic material of two individuals combines to produce offspring that are genetically different from their parents.
• During sexual reproduction the male gamete (sperm) may be placed inside the female’s body for internal fertilization, or the sperm and eggs may be released into the environment for external fertilization
• Animals produce offspring through asexual or sexual reproduction.
• asexual when one individual produce genetically identical offspring
• sexual when the genetic material from two individuals is combined to produce genetically diverse offspring.
• In a stable or predictable environment, asexual reproduction is an effective means of reproduction because all the offspring will be adapted to that environment.
• In an unstable or unpredictable environment asexually- reproducing species may be at a disadvantage because all the offspring are genetically identical and may not have the genetic variation to survive in new or different conditions.
• An additional advantage of asexual reproduction is that colonization of new habitats may be easier when an individual does not need to find a mate to reproduce.
• Fission, also called binary fission, occurs in prokaryotic microorganisms and in some invertebrate, multi-celled organisms. After a period of growth, an organism splits into two separate organisms.
• Budding is a form of asexual reproduction that results from the outgrowth of a part of a cell or body region leading to a separation from the original organism into two individuals.
• Fragmentation is the breaking of the body into two parts with subsequent regeneration. If the animal is capable of fragmentation, and the part is big enough, a separate individual will regrow.
• Parthenogenesis is a form of asexual reproduction where an egg develops into a complete individual without being fertilized.
• Sexual reproduction is the combination of (usually haploid) reproductive cells from two individuals to form a third (usually diploid) unique offspring.
• Hermaphroditism occurs in animals where one individual has both male and female reproductive parts.
• Mammalian sex determination is determined genetically by the presence of X and Y chromosomes.
• Individuals homozygous for X (XX) are female and heterozygous individuals (XY) are male.
• Avian sex determination is dependent on the presence of Z and W chromosomes.
• Homozygous for Z (ZZ) results in a male and heterozygous (ZW) results in a female.
• Sex determination in some crocodiles and turtles, for example, is often dependent on the temperature during critical periods of egg development. This is referred to as environmental sex determination, or more specifically as temperature-dependent sex determination.
• If the individual is female first, it is termed protogyny or “first female,” if it is male first, its termed protandry or “first male.”