Flashcards in Chapter 13 - Meiosis Deck (25):
What is Asexual Reproduction?
A single parent is the sole parent and passes copies of all its genes to its offspring without the fusion of gametes.
What is Sexual Reproduction?
Two parents give rise to offspring that will have unique combinations of genes inherited from the two parents.
What are genes?
Genes are coded information in the form of hereditary units
What are Gametes?
They are the reproductive cells in plants and animals (sperm and egg)
How many chromosomes do humans have?
Humans have 22 pairs of chromosomes called autosomes and 1 pair of sex chromosomes X and Y.
What are Homologous chromosomes?
The two copies of a chromosome (same length, centromere position, and staining pattern) that carry genes controlling the same inherited characters.
What are Karyotypes?
Display of stained chromosomes that is organized by size, banding pattern, location of centromere.
What is meiosis? and where does it occur?
Meiosis is similar to Mitosis but instead of doubling the number of chromosomes for coding, Meiosis will reduce the number of sets of chromosomes from two to one in the gametes. Which will counterbalance the doubling that occurs at fertilization. Meiosis occurs in the sexual reproduction stages. Meiosis occurs in the fertilization and the gametes.
What is the result of meiosis?
As a reault of meiosis, each human sperm and egg is haploid (n=23). Fertilization restores the diploid condition by combining two haploid sets of chromosomes, and the human life cycle is repeated.
What is the difference between a haploid and diploid cell?
Haploid will only contain one set of chromosomes (n=23) while diploids will have two chromosome sets in a cell (2n=46)
What are some examples of a haploid and diploid cell?
Gametes are haploid cells; Everything after anaphase 1 in the meiosis process will be a haploid cell
Cells after fertilization is a diploid cell.
What are the phases of Meiosis I?
Prophase I, Metaphase I, Anaphase I, Telophase I and Cytokinesis
What are the phases of Meiosis II?
Prophase II, Metaphase II, Anaphase II, Telophase II and Cytokinesis
What is the difference between Meiosis I and II and Mitosis?
Meiosis, like mitosis, is preceded by the duplication of chromosomes. However, this single duplication is followed by two consecutive cell divisions.
- Meiosis will have four daughter cells instead of two and only half as many chromosomes as the parent cells.
What happens in Prophase I?
Centrosomes move, the spindles form and the nuclear envelope breakdown occur.
- Chromosomes condense progressively throughout prophase I
- Each chromosome pairs with its homolog, aligned gene by gene and crossing over occurs: The DNA molecules of non-sister chromatids are broken (by proteins) and are rejoined to each other.
- Later in Prophase I microtubules from one pole or the other will attach to the two kinetochores. The homologous pairs will then move towards the metaphase plate.
What happens in Metaphase I?
Pairs of homologous chromosomes are now arranged at the metaphase plate (lined up in a line), with one chromosome in each pair facing each pole. (red chromosomes one way blue the other; Not always the same direction)
What happens in Anaphase I?
The breakdown of proteins that are responsible for sister chromatid cohesion along chromatid arms allows homologs to separate.
- The homologs move toward opposite poles
- Sister chromatid cohesion persists at the centromere, causing chromatids to move together to the same pole.
What happens in Telophase I?
When telophase I begins each half of the cell will have a complete haploid set of duplicated chromosomes. (Each chromosome is composed of two sister chromatids; one or both chromatids include a region of nonsister chromatid DNA)
What happens in Cytokinesis of Meiosis I?
Cytokinesis usually occurs simultaneously with telophase I, forming to HAPLOID (23 chromosomes) daughter cells.
What happens in Meiosis 2?
In meiosis II the same process happens but each daughter cell from meiosis I will only have half as many chromosomes. In Anaphase II the sister chromatids will separate and the chromatids will move toward opposite poles as individual (one) chromosome. At Telophase II both cells will start to split again each will have a haploid set of (unduplicated) chromosomes.
What is the difference between a Homologous pair and a sister chromatid.
A homologous pair refers to the pair of sister chromosomes from both parents that are bound together. a sister chromatid refers to the pair of chromatids that come from the same parent that are bound together.
What is crossing-over? When and How does it happen?
Crossing over happens in prophase I when two sister chromosomes (one from both parents) bind to each other and synapsis occurs.
What is genetic variation? and how does it happen?
Genetic Variation is important to survival of a species. It is the different variations of chromosome that are found in daughter cells because of Crossing over, Independent assortment and random fertilization.
What is Independent Assortment?
The variation that happens without crossing over. The four daughter cells will have equal representation of chromosomes without any other change in individual chromosomes.