| 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 |
| 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 |
| alleles | alternate forms of a gene |
| synaptonemal complex | when homologous chromosomes come together and line up side by side, forming a nucleoprotein lattice |
| synapsis | the process by which the two homologues become linked, results in a bivalent (or tetrad) |
| crossing-over | exchange of genetic material between non-sister chromatids |
| genetic recombination | chromosomes with recombined alleles in the daughter cells will produce offspring with different sets of alleles |
| independent assortment | homologues align at the metaphase plate in a random fashion, with either the maternal or paternal homologue facing either pole |
| fertilization | union of male and female gametes |
| parthogenesis | a form of asexual reproduction where only one parent contributes genetic information and crossing-over occurs between almost identical sister chromatids |
| 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 |
| Interkinesis | a short rest period in between Meiosis I and II, DNA is not copied like it is in Interphase |
| 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 spermatids undergo differentiation to form sperm cells |
| Oogenesis | After meiosis, the completion of oogenesis, and the entrance of a sperm, there is one egg (containing most of the cytoplasm) and three polar bodies |
| nondisjunction | A failure of chromosomes to separate in meiosis I or II |
| euploidy | The correct number of chromosomes for a species |
| Aneuploidy | A change in the chromosome number resulting from nondisjunction during meiosis |
| 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 |
| deletion | Occurs when the end of a chromosome breaks off or when two simultaneous breaks lead to the loss of an internal segment |
| duplication | The presence of an extra chromosomal segment |
| inversion | A segment of a chromosome has flipped and the sequence of genes is reversed |
| translocation | A movement of a chromosome segment from one nonhomologous chromosome to another, can be balanced, meaning a reciprocal swap, or can be unbalanced |
