full transcript

From the Ted Talk by Aaron Reedy: Sex determination More complicated than you thought

Unscramble the Blue Letters

My wife is pregnant right now with our first child, and when people see her with her big baby bump, the first qsutoein people ask, almost without fail, is, "Is it a boy or is it a girl?" Now, there are some assumptions behind that question that we take for granted because of our fritlaimaiy with our own haumn biology. For human babies, we take it for granted that there's a 50/50 chance of either answer, boy or girl. But why is it that way? Well, the aesnwr depends on the sex determination system that has evolved for our species. You see, for most mammals, the sex of a baby is determined genetically with the XY cmroosmohe system. mlmmaas have a pair of sex chromosomes, one passed down from mom, and one from dad. A pair of X's gives us a girl, and an X and a Y together gives us a boy. Since females only have X's to pass on in their egg clles, and males can give either an X or a Y in their sperm cells, the sex is determined by the father and the chance of producing a male or a female is 50/50. This system has worked well for mammals, but throughout the tree of life, we can see other systems that have worked just as well for other animals. There are other groups of animals that also have genetic sex determination, but their systems can be pretty different from ours. brdis and some reptiles have their sex geicleatnly determined, but instead of the sex being determined by dad, their sex is determined by mom. In those groups, a pair of Z sex chemomrsoos produces a male, so these males only have Z's to give. However, in these animals, one Z and one W chromosome together, as a pair, produces a female. In this system, the chance of a male or a female is still 50/50, it just depends on whether mom puts a Z or a W into her egg. Certain groups have taken gieetnc sex determination in completely other directions. Ants, for example, have one of the most interesting systems for deinnritemg sex, and because of it, if you are a male ant, you do not have a fhater. In an ant cnooly, there are dairtamc divisions of labor. There are soldiers that defend the colony, there are workers that cellcot food, clean the nest and care for the young, and there's a queen and a small group of male rrcideutpveos. Now, the queen will mate and then srtoe srpem from the males. And this is where the system gets really interesting. If the queen uses the setrod sperm to fertilize an egg, then that egg will grow up to become female. However, if she lays an egg without fertilizing it, then that egg will still grow up to be an ant, but it will always be a male. So you see, it's impossible for male ants to have ferhtas. And male ants live their life like this, with only one copy of every gene, much like a walking sex cell. This system is called a holaioppidld system, and we see it not only in ants, but also in other hhlgiy sioacl insects like bees and wasps. Since our own sex is determined by gnees, and we do know of these other animals that have their sex deenimetrd by genes, it's easy to assume that for all animals the sex of their babies still must be determined by genetics. However, for some animals, the question of whether it will be a boy or a girl has nothing to do with genes at all, and it can depend on something like the weather. These are animals like alligators and most turtles. In these animals, the sex of an embryo in a developing egg is determined by the temperature. In these species, the sex of the baby is not yet determined when the egg is laid, and it remains undetermined until sometime in the middle of the overall development piroed, when a critical time is reached. And during this time, the sex is completely determined by tuarepmrete in the nest. In painted turtles, for example, warm temperatures above the critical temperature will produce flmaees within the eggs, and cool temperatures will produce a male. I'm not sure who came up with this monmenic, but you can remember that when it comes to painted turtles, they are all hot ckchis and cool dudes. For some tropical fish, the question of will it be a boy or will it be a girl isn't settled until even later in life. You see, clownfish all sratt out their lives as males, However, as they matrue, they become female. They also spend their lives in smlal groups with a sirtct dominance hircaerhy where only the most dninoamt male and female reproduce. And anigmzaly, if the dominant female in the group dies, the lasrget and most dominant male will then quickly become female and take her place, and all of the other males will move up one rank in the hierarchy. In another very different oecan animal, the green spoonworm, the sex of the babies is determined by a completely different aspect of the environment. For this species, it is simply a mettar of where a lrvaa happens to randomly fall on the sea floor. If a larva lands on the open sea foolr, then it will become a female. But if it lands on top of a female, then it will become a male. So for some sepeics, the question of boy or girl is answered by genetics. For others, it's answered by the environment. And for others still, they don't even bother with the question at all. Take whiptail lizards, for example. For those desert lizards, the answer is easy. It's a girl. It's always a girl. They are a nearly all-female species, and although they still lay eggs, these eggs hatch out flmeae clones of themselves. So will it be a girl or will it be a boy? Throughout the entire animal kingdom, it does really all depend on the system of sex determination. For humans, that system is a genetic XY stseym. And for me and my wife, we found out it's going to be a baby boy. (Kiss)

Open Cloze

My wife is pregnant right now with our first child, and when people see her with her big baby bump, the first ________ people ask, almost without fail, is, "Is it a boy or is it a girl?" Now, there are some assumptions behind that question that we take for granted because of our ___________ with our own _____ biology. For human babies, we take it for granted that there's a 50/50 chance of either answer, boy or girl. But why is it that way? Well, the ______ depends on the sex determination system that has evolved for our species. You see, for most mammals, the sex of a baby is determined genetically with the XY __________ system. _______ have a pair of sex chromosomes, one passed down from mom, and one from dad. A pair of X's gives us a girl, and an X and a Y together gives us a boy. Since females only have X's to pass on in their egg _____, and males can give either an X or a Y in their sperm cells, the sex is determined by the father and the chance of producing a male or a female is 50/50. This system has worked well for mammals, but throughout the tree of life, we can see other systems that have worked just as well for other animals. There are other groups of animals that also have genetic sex determination, but their systems can be pretty different from ours. _____ and some reptiles have their sex ___________ determined, but instead of the sex being determined by dad, their sex is determined by mom. In those groups, a pair of Z sex ___________ produces a male, so these males only have Z's to give. However, in these animals, one Z and one W chromosome together, as a pair, produces a female. In this system, the chance of a male or a female is still 50/50, it just depends on whether mom puts a Z or a W into her egg. Certain groups have taken _______ sex determination in completely other directions. Ants, for example, have one of the most interesting systems for ___________ sex, and because of it, if you are a male ant, you do not have a ______. In an ant ______, there are ________ divisions of labor. There are soldiers that defend the colony, there are workers that _______ food, clean the nest and care for the young, and there's a queen and a small group of male _____________. Now, the queen will mate and then _____ _____ from the males. And this is where the system gets really interesting. If the queen uses the ______ sperm to fertilize an egg, then that egg will grow up to become female. However, if she lays an egg without fertilizing it, then that egg will still grow up to be an ant, but it will always be a male. So you see, it's impossible for male ants to have _______. And male ants live their life like this, with only one copy of every gene, much like a walking sex cell. This system is called a ____________ system, and we see it not only in ants, but also in other ______ ______ insects like bees and wasps. Since our own sex is determined by _____, and we do know of these other animals that have their sex __________ by genes, it's easy to assume that for all animals the sex of their babies still must be determined by genetics. However, for some animals, the question of whether it will be a boy or a girl has nothing to do with genes at all, and it can depend on something like the weather. These are animals like alligators and most turtles. In these animals, the sex of an embryo in a developing egg is determined by the temperature. In these species, the sex of the baby is not yet determined when the egg is laid, and it remains undetermined until sometime in the middle of the overall development ______, when a critical time is reached. And during this time, the sex is completely determined by ___________ in the nest. In painted turtles, for example, warm temperatures above the critical temperature will produce _______ within the eggs, and cool temperatures will produce a male. I'm not sure who came up with this ________, but you can remember that when it comes to painted turtles, they are all hot ______ and cool dudes. For some tropical fish, the question of will it be a boy or will it be a girl isn't settled until even later in life. You see, clownfish all _____ out their lives as males, However, as they ______, they become female. They also spend their lives in _____ groups with a ______ dominance _________ where only the most ________ male and female reproduce. And _________, if the dominant female in the group dies, the _______ and most dominant male will then quickly become female and take her place, and all of the other males will move up one rank in the hierarchy. In another very different _____ animal, the green spoonworm, the sex of the babies is determined by a completely different aspect of the environment. For this species, it is simply a ______ of where a _____ happens to randomly fall on the sea floor. If a larva lands on the open sea _____, then it will become a female. But if it lands on top of a female, then it will become a male. So for some _______, the question of boy or girl is answered by genetics. For others, it's answered by the environment. And for others still, they don't even bother with the question at all. Take whiptail lizards, for example. For those desert lizards, the answer is easy. It's a girl. It's always a girl. They are a nearly all-female species, and although they still lay eggs, these eggs hatch out ______ clones of themselves. So will it be a girl or will it be a boy? Throughout the entire animal kingdom, it does really all depend on the system of sex determination. For humans, that system is a genetic XY ______. And for me and my wife, we found out it's going to be a baby boy. (Kiss)

Solution

  1. store
  2. sperm
  3. female
  4. amazingly
  5. small
  6. human
  7. mammals
  8. chicks
  9. genetically
  10. species
  11. fathers
  12. colony
  13. father
  14. reproductives
  15. determined
  16. collect
  17. social
  18. mnemonic
  19. dramatic
  20. larva
  21. hierarchy
  22. females
  23. mature
  24. period
  25. dominant
  26. matter
  27. answer
  28. floor
  29. birds
  30. familiarity
  31. chromosomes
  32. cells
  33. highly
  34. largest
  35. determining
  36. genes
  37. chromosome
  38. temperature
  39. question
  40. system
  41. strict
  42. genetic
  43. stored
  44. ocean
  45. haplodiploid
  46. start

Original Text

My wife is pregnant right now with our first child, and when people see her with her big baby bump, the first question people ask, almost without fail, is, "Is it a boy or is it a girl?" Now, there are some assumptions behind that question that we take for granted because of our familiarity with our own human biology. For human babies, we take it for granted that there's a 50/50 chance of either answer, boy or girl. But why is it that way? Well, the answer depends on the sex determination system that has evolved for our species. You see, for most mammals, the sex of a baby is determined genetically with the XY chromosome system. Mammals have a pair of sex chromosomes, one passed down from mom, and one from dad. A pair of X's gives us a girl, and an X and a Y together gives us a boy. Since females only have X's to pass on in their egg cells, and males can give either an X or a Y in their sperm cells, the sex is determined by the father and the chance of producing a male or a female is 50/50. This system has worked well for mammals, but throughout the tree of life, we can see other systems that have worked just as well for other animals. There are other groups of animals that also have genetic sex determination, but their systems can be pretty different from ours. Birds and some reptiles have their sex genetically determined, but instead of the sex being determined by dad, their sex is determined by mom. In those groups, a pair of Z sex chromosomes produces a male, so these males only have Z's to give. However, in these animals, one Z and one W chromosome together, as a pair, produces a female. In this system, the chance of a male or a female is still 50/50, it just depends on whether mom puts a Z or a W into her egg. Certain groups have taken genetic sex determination in completely other directions. Ants, for example, have one of the most interesting systems for determining sex, and because of it, if you are a male ant, you do not have a father. In an ant colony, there are dramatic divisions of labor. There are soldiers that defend the colony, there are workers that collect food, clean the nest and care for the young, and there's a queen and a small group of male reproductives. Now, the queen will mate and then store sperm from the males. And this is where the system gets really interesting. If the queen uses the stored sperm to fertilize an egg, then that egg will grow up to become female. However, if she lays an egg without fertilizing it, then that egg will still grow up to be an ant, but it will always be a male. So you see, it's impossible for male ants to have fathers. And male ants live their life like this, with only one copy of every gene, much like a walking sex cell. This system is called a haplodiploid system, and we see it not only in ants, but also in other highly social insects like bees and wasps. Since our own sex is determined by genes, and we do know of these other animals that have their sex determined by genes, it's easy to assume that for all animals the sex of their babies still must be determined by genetics. However, for some animals, the question of whether it will be a boy or a girl has nothing to do with genes at all, and it can depend on something like the weather. These are animals like alligators and most turtles. In these animals, the sex of an embryo in a developing egg is determined by the temperature. In these species, the sex of the baby is not yet determined when the egg is laid, and it remains undetermined until sometime in the middle of the overall development period, when a critical time is reached. And during this time, the sex is completely determined by temperature in the nest. In painted turtles, for example, warm temperatures above the critical temperature will produce females within the eggs, and cool temperatures will produce a male. I'm not sure who came up with this mnemonic, but you can remember that when it comes to painted turtles, they are all hot chicks and cool dudes. For some tropical fish, the question of will it be a boy or will it be a girl isn't settled until even later in life. You see, clownfish all start out their lives as males, However, as they mature, they become female. They also spend their lives in small groups with a strict dominance hierarchy where only the most dominant male and female reproduce. And amazingly, if the dominant female in the group dies, the largest and most dominant male will then quickly become female and take her place, and all of the other males will move up one rank in the hierarchy. In another very different ocean animal, the green spoonworm, the sex of the babies is determined by a completely different aspect of the environment. For this species, it is simply a matter of where a larva happens to randomly fall on the sea floor. If a larva lands on the open sea floor, then it will become a female. But if it lands on top of a female, then it will become a male. So for some species, the question of boy or girl is answered by genetics. For others, it's answered by the environment. And for others still, they don't even bother with the question at all. Take whiptail lizards, for example. For those desert lizards, the answer is easy. It's a girl. It's always a girl. They are a nearly all-female species, and although they still lay eggs, these eggs hatch out female clones of themselves. So will it be a girl or will it be a boy? Throughout the entire animal kingdom, it does really all depend on the system of sex determination. For humans, that system is a genetic XY system. And for me and my wife, we found out it's going to be a baby boy. (Kiss)

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
sex determination 3
genetic sex 2
male ants 2
dominant male 2

Important Words

  1. alligators
  2. amazingly
  3. animal
  4. animals
  5. answer
  6. answered
  7. ant
  8. ants
  9. aspect
  10. assume
  11. assumptions
  12. babies
  13. baby
  14. bees
  15. big
  16. biology
  17. birds
  18. bother
  19. boy
  20. bump
  21. called
  22. care
  23. cell
  24. cells
  25. chance
  26. chicks
  27. child
  28. chromosome
  29. chromosomes
  30. clean
  31. clones
  32. clownfish
  33. collect
  34. colony
  35. completely
  36. cool
  37. copy
  38. critical
  39. dad
  40. defend
  41. depend
  42. depends
  43. desert
  44. determination
  45. determined
  46. determining
  47. developing
  48. development
  49. dies
  50. directions
  51. divisions
  52. dominance
  53. dominant
  54. dramatic
  55. dudes
  56. easy
  57. egg
  58. eggs
  59. embryo
  60. entire
  61. environment
  62. evolved
  63. fail
  64. fall
  65. familiarity
  66. father
  67. fathers
  68. female
  69. females
  70. fertilize
  71. fertilizing
  72. fish
  73. floor
  74. food
  75. gene
  76. genes
  77. genetic
  78. genetically
  79. genetics
  80. girl
  81. give
  82. granted
  83. green
  84. group
  85. groups
  86. grow
  87. haplodiploid
  88. hatch
  89. hierarchy
  90. highly
  91. hot
  92. human
  93. humans
  94. impossible
  95. insects
  96. interesting
  97. kingdom
  98. kiss
  99. labor
  100. laid
  101. lands
  102. largest
  103. larva
  104. lay
  105. lays
  106. life
  107. live
  108. lives
  109. lizards
  110. male
  111. males
  112. mammals
  113. mate
  114. matter
  115. mature
  116. middle
  117. mnemonic
  118. mom
  119. move
  120. nest
  121. ocean
  122. open
  123. painted
  124. pair
  125. pass
  126. passed
  127. people
  128. period
  129. place
  130. pregnant
  131. pretty
  132. produce
  133. produces
  134. producing
  135. puts
  136. queen
  137. question
  138. quickly
  139. randomly
  140. rank
  141. reached
  142. remains
  143. remember
  144. reproduce
  145. reproductives
  146. reptiles
  147. sea
  148. settled
  149. sex
  150. simply
  151. small
  152. social
  153. soldiers
  154. species
  155. spend
  156. sperm
  157. spoonworm
  158. start
  159. store
  160. stored
  161. strict
  162. system
  163. systems
  164. temperature
  165. temperatures
  166. time
  167. top
  168. tree
  169. tropical
  170. turtles
  171. undetermined
  172. walking
  173. warm
  174. wasps
  175. weather
  176. whiptail
  177. wife
  178. worked
  179. workers
  180. xy
  181. young