| A | B |
|---|
| homologous chromosomes (homologues) | have the same length and centromere position, have similar banding patterns because they contain genes for the same traits. One homolog came from the egg and one came from the sperm |
| meiosis | type of nuclear division that reduces the chromosome number from diploid to haploid and includes 2 divisions |
| diploid (2n) | organism or cell has two sets of chromosomes, one from the egg and one from the sperm |
| haploid (n) | organism or cell has one set of chromosome |
| gametes | reproductive cells (eggs and sperm), haploid |
| sexual reproduction | haploid gametes merge into a diploid cell called a zygote |
| zygote | fertilized egg, diploid cell of offspring after sexual reproduction |
| crossing-over | exchange of genetic material between non-sister chromatids |
| recombinant gametes | mixed chromosome that contains some of Mom's and Dad's genes due to crossing over |
| independent assortment | homologous chromosomes align at the metaphase plate in a random fashion, with either the maternal or paternal homologue facing either pole |
| fertilization | union of male (sperm) and female (egg) gametes |
| sister chromatids | identical copies of DNA attached at the centromere after DNA replication |
| Prophase I | chromosomes are visible, attached to one another (synapsis) in bivalents, crossing-over occurs, centrosomes move to opposite sides as spindle forms, nucleolus disappears, nuclear membrane fragments |
| Metaphase I | homoloogous chromosomes line up in pairs in the center--independent assortment |
| Anaphase I | homologous chromosomes split apart and move to opposite sides, sister chromatids do not split |
| Telophase I | spindle disappears, nuclei form, cytokinesis may or may not occur |
| Prophase II | cells have one chromosome from each homologous pair (still a double chromosome) |
| Metaphase II | Chromosomes composed of two sister chromatids line up independently |
| Anaphase II | Sister chromatids split at the centromere and move to opposite poles attached to spindles |
| Telophase II | spindle disappears, nuclei form, cytokinesis occurs |
| Meiosis I | two unique haploid cells result, each chromosome still contains 2 sister chromatids |
| Meiosis II | 4 haploid cells result, each containing a single chromosome for each type |
| Spermatogenesis | After meiosis, haploid gametes undergo differentiation to form sperm cells with flagella |
| Oogenesis | After meiosis, haploid gametes become 1 large ova and 3 polar bodies |
| nondisjunction | A failure of chromosomes to separate in meiosis I or II |
| monosomy | an individual has only 1 of a particular chromosome instead of 2 (2n-1) |
| trisomy | an individual has 3 of a particular chromosome instead of 2 (2n+1) |
| Trisomy 21 | down syndrome, mental retardation, short stature, flat face, stubby fingers |
| karyotype | a visual display of the chromosomes arranged by size, shape, and banding pattern |
| XO (monosomy X) | Turner syndrome, females are shorter, have undeveloped sexual characteristics and are sterile |
| XXY | Klinefelter' syndrome, males have some female characteristics and are sterile |
| genetic variation | The processes of crossing over, independent assortment, and random fertilization create unique offspring |
| parental gametes | chromosomes that did not cross over and therefore resemble one of the two parents |
| XXX | Triple X syndrome |
