three origins of genetic variation
crossing over, independent assortment, random fertilization
When does crossing over occur?
prophase I of meiosis
Where does crossing over occur?
What occurs during crossing over?
pair of nonsister homologous chromosomes exchange corresponding segments of genetic material
What happens as a result of crossing over?
After these two chromosomes have exchanged genetic material, they are genetically unique-- neither is exactly like a parent
When does independent assortment of homologues occur?
metaphase I/anaphase I of meiosis (chromosomes positioned along metaphase plate as pairs of chromosomes; each pair consists of one maternal and one paternal chromosome)
What does independent assortment of homologues mean?
-the orientation of pairs of homologous chromosomes is random -random which chromosome (maternal or paternal) will go to which pole -each pair of homolougous chromosomes positioned independently of other pairs, so each pair is randomly assorted into daughter cells independently of other pairs
male and female gametes
sperm and ovaries
-combinations of gametes from two individuals results in new combinations and genetic variation -variation results from which sperm randomly fertilizes which egg -because of independent assortment, each male and female gamete has millions of possible chromosome combinations
Why is genetic variation so important?
if an environmental change occurs, then individuals in a population with alleles that prove advantageous in these conditions (but those without the advantage would not survive). if all members of the population were exactly the same, then all could die. Genetic diversity is important for a population's stability.