2.1 A Closer Look at Variation PDF

2.0 As species reproduce, characteristics are passed on from parents to offspring. 2.1 A Closer Look at Variation  Variation Variation is one of the most critical aspects of species survival. This variation may not always be as easy to observe as color is because it m...

2.0 As species reproduce, characteristics are passed on from parents to offspring. 2.1 A Closer Look at Variation  Variation Variation is one of the most critical aspects of species survival. This variation may not always be as easy to observe as color is because it may be a behavioral tendency or a genetic (cellular code) modification that enables some individuals within a species to survive while others of the species will perish. These penguins may look almost identical, but they vary from one another in subtle ways.  Traits The characteristics that an organism inherits from its parents are called traits. Ex. hair and eye color, blood group, nose and lip shape, straight or weird bending thumb etc.  Heritable Characteristics Heritable characteristics are those traits which are passed down directly from parent to offspring; these traits are inherited. These traits are passed on by way of the genetic material that is combined from the parents during the process of sexual reproduction. Heritable traits include, structural and distinguishing characteristics such as eye color, hair type, skin color and earlobes.  Heritable Characteristics Can be: -same as both parents -different from both parents -intermediate (between) both parents -same as just dad -same as just mom *Think about your own biological families.  Non-Heritable Characteristics Non-heritable characteristics are acquired. They are not passed on from generation to generation The ability to play an instrument, or any skill learned during a lifetime that is not passed down to offspring. Ex. soccer skills  Discrete Variations Discrete variations are differences in characteristics that have a definite form. This is the “either/or” form of a characteristic. There is a limited number of possibilities (ex. 2 possibilities, 4 possibilities with no other possibilities, etc.). Discontinuous It usually results when a trait is controlled by only a single gene and when there is little/no environmental or ‘nurture’ (non-genetic) influence on a trait Ex. your life choices do not affect your blood type, which is determined by only a single gene (with 3 different alleles: A, B, & O) Example tongue roller or non-tongue roller earlobes may be either attached or unattached eye color blood group (A, B, AB, O)  Continuous Variations Continuous variations are differences in characteristics that have a range of forms almost a limitless range of possibilities for a trait It usually results when many different genes affect (code for) a trait and/or when there is a large environmental or ‘nurture’ (non-genetic) influence on a trait Their combined effects allow for more variety in the appearance of a trait Ex. lots of genes contribute to our size/weight, which is also sensitive to nongenetic factors such as how much we eat and exercise The more people you measure and the smaller the range of categories you use, the closer the results will be to the curved line. The shape of this graph is called a bell curve and is the result of a variable being normally distributed. Examples height, shoe size, mass, weight, skin color, hair color, personality  Variation and the Environment Two plants that are completely identical. Then put them in separate environments. They would begin to look different. Sunny window -> green, bushy Dim closet -> pale green, spindly  Variation and the Environment Some variations are only influenced by genetics whereas other variations can be influenced by both genetics and the environment (ie. height). The variations that are influenced by interactions with the environment are not inherited. Examples include: Change in the pigmentation of skin color throughout the seasons due to the sun. Height and weight can be influenced by diet. a child of tall parents won’t grow tall if they don’t get the proper nutrition  Assignment Read textbook pages FOCUS: none SCIENCE IN ACTION: pages 26-29 Activity: Discrete Vs. Continuous Discrete Vs. Continuous Variation Bingo Investigation: Inheritance of Human Characteristics 2.1 Assignment Activity Discrete Vs. Continuous Variation Bingo Investigation (Activity)  2.1 Assignment 1. Give one example of a heritable characteristic and one example of a non-heritable characteristic. Use examples different from those in the text. 2. What is discrete variation? What is continuous variation? 3. Some characteristics are heritable but can also be affected by the environment. Explain how this is true for height in humans. 4. Describe how the environment may affect variation in plants. 5. A scientist wants to study continuous variation in a mouse population. What mouse characteristics would she or he investigate? 6. Observe your thumb and the thumbs of your classmates. You will see that there are two types: a straight thumb and a bent-backward (or hitchhiker’s) thumb. What type of variation does thumb shape show?