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Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. In many species of animals and plants, the energetic costs of reproduction are greater for females than males. The gamete (egg) is larger and more ‘expensive’, and the energy needed by the embryo to grow and develop are usually supplied by the female. To supply this energy, the female often needs to be larger than the male. The common exception to this pattern is where males battle one another for access to mates. In this case, selection favors larger males. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. In clown fish and wrasses, a dominant individual of one sex inhibits the development of other fish into that dominant sex. In Midas cichlids, the sex of an organism is determined by the presence of larger or smaller fish in the brood. Larger broodmates are assumed to be male, and stimulate the development of females. Smaller broodmates are assumed to be female, and stimulate the development of males. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. In Protenor determination, it is the number of sex chromosomes (1 or 2) that determines sex. Males have 1 sex chromosome and females have 2. Male produce sperm with 0 or 1 sex chromosome, all the eggs have 1. Fusion re-establishes the 1 or 2 condition for males and females, respectively. In Lygaeus determination, it is they type of sex chromosomes that determine sex. One sex has 2 of the same sex chromosomes (homogametic) while the other sex has 2 different sex chromosomes (heterogametic). In some species like humans, the male is heterogametic (XY) and the female is homogametic (XX). In other species like fowl, the female is heterogametic (ZW) and the male is homogametic (WW). In humans the presence of the SRY gene on the Y chromosome determines maleness. Individuals that lack the gene are female. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. 4. What is 'gender'? Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. 4. What is 'gender'? Gender is a set of behaviors that correlate, within a society, with sex. However, these correlations can vary in different societies. So, skirt wearing is associated with the gender role of women in the USA, but not in some other cultures. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. 4. What is 'gender'? 5. How do animals use sex, beside procreation? Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. 4. What is 'gender'? 5. How do animals use sex, beside procreation? Sex is a suite of behaviors that are used for procreation, but can also be used for other functions. Humans use sex for enjoyment, pair-bonding, and in exchange for money, food, or other resources. Bonobo chimps use sex for greeting and conflict resolution. Giraffes seem to use sex for establishing dominance hierarchies. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. 4. What is 'gender'? 5. How do animals use sex, beside procreation? 6. Describe a circumstance where members of one sex in animals accept the 'gender role' of the other sex. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. 4. What is 'gender'? 5. How do animals use sex, beside procreation? 6. Describe a circumstance where members of one sex in animals accept the 'gender role' of the other sex. In some birds and cuttlefish, juvenile males that are not large and mature enough to acquire their own territory may benefit from having the plumage or coloration of females. They ‘sneak’ into a dominant male’s territory using the gender role of a female, and then mate with females in that territory. So, for these males, it is adaptive (increases reproductive success) to look and act like a female when they are young. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. 4. What is 'gender'? 5. How do animals use sex, beside procreation? 6. Describe a circumstance where members of one sex in animals accept the 'gender role' of the other sex. 7. Explain why sex linkage violates the principle of independent assortment. Study Questions 1. Explain why females are often larger than males, even in species in which individuals change sex. 2. Provide an example of social sex determinism. 3. Describe Protenor and Lygaeus sex determination. 4. What is 'gender'? 5. How do animals use sex, beside procreation? 6. Describe a circumstance where members of one sex in animals accept the 'gender role' of the other sex. 7. Explain why sex linkage violates the principle of independent assortment. The sex of an organism is a phenotypic characteristic. If this characteristic is governed by genes on a particular chromosome, then this trait will be inherited along with the other genes on that chromosome that influence other traits. As such, the trait of ‘sex’ is not inherited independently of these other traits – they are part of the same DNA molecule and will be inherited together. Study Questions 8. Consider this cross: AaXBY x AaXBXb - the ‘A’ gene is obviously inherited independently of sex and the sex-linked B gene, because A is NOT sex linked (so it is on an autosomal chromosomes and will necessarily assort independently). Assume complete dominance for A and B. - How many types of gametes can the male make with respect to these loci? - How many phenotypes are possible in the progeny? - What fraction of male offspring will express the Ab phenotype? Study Questions 8. Consider this cross: AaXBY x AaXBXb - the ‘A’ gene is obviously inherited independently of sex and the sex-linked B gene, because A is NOT sex linked (so it is on an autosomal chromosomes and will necessarily assort independently). Assume complete dominance for A and B. - How many types of gametes can the male make with respect to these loci? The male can make 4 types of gametes: AXB, AY, aXB, aY - How many phenotypes are possible in the progeny? At the A locus, 2 phenotypes are possible (A, a). At B and with respect to sex, 3 are possible (B daughters, B sons, b sons). So, there are 6 possible phenotypes in the progeny (2 x 3). - What fraction of male offspring will express the Ab phenotype? ¾ A x ½ sons b = 3/8 of the sons will be Ab. While ¼ of the offspring are b sons, the question asks about just the fraction of sons. ½ the sons are b….