Biol 301 1nd Edition Lecture 10 Outline of Last Lecture I. AdaptationsII. Migration/ Storage/ DormancyIII. Variation in foodIV. Life History TraitsOutline of Current Lecture II. ReproductionIII. Sexual StrategiesIV. Sex DeterminationV. Mating SystemsVI. Sexual SelectionCurrent LectureReproduction- Sexual reproduction: a reproduction mechanism in which progeny inherit DNA from two parents.- Gonads: the primary sexual organs in animals.- Sexual gametes are produced through meiosis, which results in haploid cells containing a single full set of chromosomes. Haploid gametes fuse together to produce a diploid zygote. The distribution of parent chromosomes into the haploid cells is generally random. Mixing of the chromosomes from the two parents results in new combinations of genes in the offspring.- Asexual reproduction: a reproduction mechanism in which progeny inherit DNA from a single parent.- Vegetative reproduction: a form of asexual reproduction in which an individual is produced from the nonsexual tissues of a parent. Many plants reproduce vegetatively from leaf, root, or rhizome tissue (e.g., walking ferns).- Clones: individuals that descend asexually from the same parent and bear the same genotype.- Parthenogenesis: a form of asexual reproduction in which an embryo is produced without fertilization. Animals that reproduce by parthenogenesis are typically all female. Relatively These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.rare in vertebrates. A few examples exist, such as the female boa constrictor that gave birth to two litters of daughters through parthenogenesis. - Sexual organs require considerable energy and resources.- Mating behaviors (e.g., floral displays, courtship rituals) require time and energy, and increase risk of herbivory, predation, and parasitism.- Cost of meiosis: the 50% reduction in the number of a parent’s genes passed on to the next generation via sexual reproduction versus asexual production; occurs because sexual genes are haploid.- The cost of meiosis can be counterbalanced by hermaphroditism, which is when an individual possesses both male and female gametes. Individuals can contribute one set of genes to offspring via female function and one set via male function.- Costs of sexual reproduction can also be offset if the male helps the female take care of offspring, reducing female energy costs.- Purging mutations: Sexually reproducing organisms can lose deleterious mutations during meiosis. Due to random assortment, many gametes will not contain mutations. The fusion oftwo gametes with the same mutation will result in an offspring that is homozygous recessivefor that mutation; it is likely that this offspring will not be viable. Asexual organisms do not have any means of purging mutations. Phylogenetic studies demonstrate that the long-term evolutionary persistence of asexual populations appears to be low.- Coping with environmental variation: offspring are likely to encounter different environmental conditions than their parents did. Offspring with genetic variation resulting from sexual reproduction have an increased probability of possessing gene combinations that will help them adapt to different conditions.- Coping with parasites and pathogens: pathogens have much shorter generation times and larger population sizes than the host species they infect. This allows pathogens to evolve ways around host defenses, and forces hosts to rapidly evolve new defenses.- Red Queen Hypothesis: sexual selection allows hosts to evolve at a rate that counters the rapid evolution of parasites.Sexual Strategies- Most vertebrates and some plants have separate sexes; most plants and some vertebrates are hermaphrodites.- Perfect flowers: flowers that contain both male and female flowers.- Simultaneous hermaphrodites: individuals that possess male and female reproductive functions at the same time.- Sequential hermaphrodites: individuals that possess male or female reproductive function and then switch to the other.- Monoecious: plants that have separate male and female flowers on the same individual.- Dioecious: plants that contain either only male flowers or only female flowers on a single individual.- For hermaphrodites, self-fertilization (i.e., selfing) occurs when an individual’s male gametes fertilize its own female gametes. Since this poses a cost due to inbreeding depression, selection should favor individuals that can breed with other individuals (i.e., outcrossing) when possible. Sequential hermaphroditism avoids the problem of selfing by separating sexual functions in time. Some species have self-incompatibility genes that prevent an organism from being able to self.- Some species are able to switch between outcrossing and selfing. When mates are available,individuals outcross. When mates are unavailable, individuals self-fertilize; this may not produce as many viable offspring, but it is better than nothing. Mixed mating can be in response to a lack of resources in the environment.Sex Determination- In organisms with separate sexes, the sex ratio of male to female offspring is often one to one. Sex is often determined by inheritance of sex-specific chromosomes (e.g., human females have two X chromosomes (XX); males are XY). The sex that possesses two different chromosomes will produce an approximately equal number of gametes with each chromosome.- On average, half of all offspring will be male; half will be female. In some, sex is determined by the presence or absence of a sex-specific chromosome. In bees, ants, and wasps, sex is determined by whether or not eggs are fertilized (haplodiploidy).- Environmental sex determination: a process in which largely the environment determines sex; this is a type of phenotypic plasticity, where the phenotype is sex.- Temperature-dependent sex determination occurs when the temperature at which eggs determines the sex of an individual. Females can influence the sex ratios of their offspring.- In most species, the sex ratio of males to females is nearly even.- Frequency dependent selection: when the rarer phenotype in a population is favored by natural selection.- In a population with an uneven sex ratio, the rarer sex will compete with fewer individuals for breeding; consequently, the rarer sex will experience higher fitness. Mothers that