1What is the difference between a gene and an allele?
a gene is a general trait (for example: eye color), an allele is a specific trait; a different verison of the gene (for example: blue or brown eyes)
2What are autosomes?
pairs of chromosomes that are the same in male and female
3What are sex chromosomes?
sets of chromosomes that differ between the sexes and contain the genes that determine gender
4What two kinds of cells are haploid in humans?
egg and sperm cells (the sex cells, gametes)
5Give an example of a diploid cell
body cells, i.e. muscle cells
6What is 'n'?
haploid chromosome number in gametes
7What is '2n'?
the diploid chromosome number in somatic cells
9somantic cells
body cells
10meiosis
a type of nuclear division that is important in sexual reproduction
11Why is it important that the chromosome number is halved before fertilization?
because if it wasnt the gametes would contain the same number of chromosomes as the body cells, and the number of chromosomes would double with each new generation and eventually the cells of sexually reproducing organisms would be nothing but chromosomes
12What is meant by independent assortment?
the random assortment of chromosomes which produces variation
13prophase I
crossing over occurs as chromosomes condense; nuclear envelope fragments
14metaphase I
homologous chromosomes pairs align independently at spindle equator; tetrads align at the spindle equator
15anaphase I
homologous chromosomes separate, move to poles
16telophase I
two haploid daughter cells formed, not identical to the parent cell
17prophase II
chromosomes condense, and the nuclear envelope fragments
18metaphase II
tetrads align at the spindle equator
19anaphase II
sister chromatids separate, becoming daughter chromosomes that move to the poles
20telophase II
four haploid daughter cells are formed that are genetically different from each other and from the parent cell
21How is meiosis I different from mitosis
meiosis I is different than mitosis in that homologues pair and separate and crossing-over occurs
22How is meiosis II like mitosis
meiosis II is similar to mitosis in that sister chromatids separate; however the resulting daughter cells are haploid
23nondisjunction
chromosomes fail to separate correctly causing an abnormal number of chromosomes
24When can nondisjunction occur?
during meiosis I when both members of a pair go into the same daughter cell or meiosis II when sister chromatids fail to separate
25What are the possible results of nondisjunction?
trisomy (3 copies of a chromosome), or monosomy (single copy of a chromosome)