BIOLOGY QUESTIONS TO HELP FOCUS YOUR BIOLOGY READING

"SEX: Society and Genes, Brain and Behavior" Lecture on 1/23/01 (notes on Web page)

Your answers to these questions are to be turned in by Thursday morning (2/1) at 9 am. You can either turn them into me (Stu) or to your seminar leader who will then give them to me. You can turn these in early, but not late. Late work will be accepted (since you need to turn these in for 4 of your credits), but not graded.

Knowledge of material on the first two study guides will help you in your preparation for the midterm.

1. Why do organisms reproduce sexually as opposed to asexually? Ans: Sexual reproduction (meiosis) produces a greater rate of mutation than asexual reproduction (mitosis). This is beneficial to organisms because it increases the chance that at least some individuals will have the ability to survive better (for example if a disease breaks out).

2. What is the difference between natural selection and sexual selection? Ans: Natural selection occurs when something in the environment makes it so that certain individuals are able to survive better, and as a result, they are able to reproduce and pass on their genes. An example of natural selection is: an outbreak of malaria kills off everyone except those who posses one copy of the sickle cell gene (two copies of the gene leads to sickle cell anemia), as a result, individuals who carry the sickle cell gene become more common in that area (but never too common). Sexual selection occurs when certain genes are passed down because a member of the opposite sex finds them appealing (for example, feather color in birds). However, evolution (that is, changes in the frequency of genes in a population) occurs from both natural and sexual selection. They are also often, but not always, related (a male bird who has lots of flashy, brightly colored feathers must be really healthy in order to survive with all the predators who see him).

3. Sociobiology (evolutionary psychology) is the study of what? Ans: Sociobiology is the study of the evolution of social traits as a result of natural selection.

4. Explain one of the following behaviors from a sociobiological perspective: maternal care, kin selection, mate selection, homosexual behavior. Ans: Maternal care: by taking care of her offspring, a mother helps ensure that her genes will be passed on. Kin selection: helping out your relatives helps ensure there are more individuals around who have many of your genes in common. Mate selection: by picking out the "best" (most able to survive) mates, it helps ensure that your offspring (who possess many of your genes) will be able to survive and reproduce. Homosexual behavior: this one is controversial, but the explanation that fits best with sociobiology is that individuals who are homosexual are able to help out with the care of their relative's children, which indirectly helps ensure that their genes will be passed on. You could also argue that over the long term it helps with population control.

5. What is the relationship between a chromosome, DNA and genes? Ans: All chromosomes are composed of DNA, organized into genes (themselves comprised of a specific sequence of DNA) that code for a particular protein.

6. How many sets of chromosomes do you have? Ans: On which one would you find the gene for testis determining factor (TDF)? Most humans have 23 pairs of chromosomes (46 total). TDF is located on the Y chromosome.

7. Explain the difference between organizational and activational effects of hormones. Ans: Hormones can have organizational effects during development. In this case, the hormone would "direct" certain cells in an embryo to differentiate and arrange themselves in a particular way. In contrast, when a hormone is activating it tells an organ or group of cells that already exists to become active. For example, testosterone in an embryo directs particular cells to become testis (organizational), and then leads to the testis beginning to produce sperm during puberty (activational).

8. What is meant by sexually dimorphic nuclei in the brain? Ans: Sexually dimorphic nuclei differ in physical structure between males and females.

9. This is just a question to write about and will not be graded: What does LeVay state accounts for sexual orientation and what are some of your views on this subject?

10. For those of you NOT at the workshop, turn in answers to the “How to Think Critically” workshop

11. Questions to look at on p. 525: review activities #4-5.

4. Ans: Gender is determined by whether or not the sperm that fertilizes an egg contains an X chromosome (girl) or Y chromosome (boy). A barr body is an inactivated X chromosome that occurs when a cell contains more than one X chromosome.
5. Ans: Metafemale: 3 X chromosomes, often sterile and may have a reduced mental capacity. Turner's syndrome: only 1 X chromosome (no Y), female, but sterile, often short in stature and with some mental impairment. Kleinfelter's syndrome: 2 X chromosomes and a Y chromosome, male, tall, underdeveloped genitalia and enlarged breasts, may have some learning disabilities.

Those who want upper division credit should obtain the other questions from me directly. You must work on these questions in a group of at least 2 persons. You will also need to participate in the peer review in groups of 2 or more.