LECTURE 1
INTRODUCTION
SEXUAL VS. ASEXUAL REPRODUCTION
I. Modes of Sexual and Asexual Reproduction
a. Sexual reproduction--fusion of male and female reproductive cells to form genetically different offspring.
Haploid
-One set of chromosomes
-23 in humans
Fusion of haploid gametes produced diploid organisms (zygote)
-produce individuals with genetic components different from parents
b. Asexual reproduction
Diploid reproductive cells producing genetically identical daughter cells (e.g., budding)
Unisexual reproduction (only at genetic level)
-parthenogenesis
*observed mostly in lizards (primarily genus Cnemidophorus).
*the entire species is exclusively female.
*each female produces diploid eggs, and mating behavior from other females triggers the diploid eggs to divide.
*offspring is genetically identical to the mother.
-gynogenesis
*occurs in som poeciilid fish and a few other fish.
*variation on parthenogenesis.
*same as parthenogenesis but the presence of sperm required to activate the diploid eggs to divide.
-hybridogenesis
*most well-known in a poeciliid fish (poeciliopsis monacha-lucida).
*individuals are diploid, one set from mother and one from father.
*during meiosis of eggs, maternal genes are retained and paternal genes discarded.
*maternal chromosomes, but not paternal chromosomes, are inherited.
*paternal chromosomes change every generation.
-polyembryony (identical twinning)
*occurs in armadillos.
*only one embryos is the result of sexual reproduction.
*remaining embryos arise from cloning of original embryos.
*all offspring from the litter are genetically identical to one another.
II. Pros and Cons of Sexual and Asexual Reproduction
a. Sexual
genetic variability enables adaptation to changing environment
best in fluctuating environment
eliminates bad genes through natural selection
evolutionarily and energetically costly
b. Asexual
no genetic variation (either good or bad)
no cost of mating and courtship
fast reproduction (higher fecundity)
only needs one to produce a colony