Meiosis Flashcards
Gamete
Sex cells (sperm or egg/ovum), haploid cells
Somatic Cell
Body cells - all cells in the body other than sex cells (skin cell, muscle cell, etc.), diploid cells
Haploid
A cell with half the number of chromosomes as parent cell, referred to as n
Diploid
Refers to twice the number of chromosomes in a gamete (2n). Every cell of the body is diploid except the sex cells. In humans the diploid number of chromosomes is 46
Sister chromatids
A chromosome and its duplicate, attached to one another by a centromere
Centromere
structure that holds chromatids (single stranded chromosome) together
Homologous pair (homologous chromosomes)
paired chromosomes similar in size and gene arrangement, but different alleles
Tetrad
a pair of homologous chromosomes each with sister chromatids.
Gene
sections of DNA that contain genetic information for the inheritance of specific traits
Allele
Different forms of the same gene (e.g., different eye colours)
Crossing over
The exchange of genetic material between homologous chromosomes
What is the purpose of meiosis?
- a process that produces cells (gametes) with half the number (haploid) of the chromosomes as the parent cell (diploid).
…Two Important Outcomes of Meiosis:
1. Genetic reduction: diploid to haploid
2. Genetic recombination: genetically distinct offspring, which increases genetic variation in a population
Explain spermatogenesis and oogenesis.
- Spermatogenesis: MALES go through a process of sperm (gamete) production called spermatogenesis.
- Oogenesis: FEMALES go through a process of egg (gamete) production called oogenesis.
What are the key events that occur at each stage of meiosis I?
…Meiosis I
1. Prophase I
- Each pair of homologous chromosomes, one from each parent, line up side by side – this is called synapsis.
- While they are lined up, they exchange genetic information in a process called crossing over.
Crossing over
- Non-sister chromatids of homologous chromosomes
exchange pieces of chromosomes.
- Can occur at a single point or several points on the chromosomes
- Occurs randomly
WHY????
- To increase genetic diversity (differences) in the gametes produced, which ultimately creates genetically distinct offspring.
2. Metaphase I
- Homologous chromosomes line up at the metaphase plate by independent assortment
- Spindle fibers attach to the centromere
Independent assortment
- The homologous chromosomes are paired because the same genes are found on each chromosome in the same location (one from Mom and one from Dad). E.g., genes for hair colour, eye colour, height
- The manner in which the homologous chromosomes line up is random (or independent from other homologous chromosomes).
3. Anaphase I
- Spindle fibers shorten and pull homologous chromosomes to opposite poles of the cell
4. Telophase I
- Sister chromatids uncoil
- Spindle fibers disappear
- Nuclear membrane forms around sister chromatids
- Two new cells form by cytokinesis
- There is little or no interphase between meiosis I and meiosis II
Explain crossing over
- Crossing over: Homologous pairs are lined up, they exchange genetic information in a process called crossing over.
- Crossing over is a cellular process that happens during meiosis when chromosomes of the same type are lined up. When two chromosomes — one from the mother and one from the father — line up, parts of the chromosome can be switched. The two chromosomes contain the same genes, but may have different forms of the genes.
Explain Independent assortment
- Independent assortment: Independent assortment means genes are like independent travelers during cell division. They don’t stick together but sort randomly into new cells. This randomness makes each new cell a unique mix, just like shuffling a deck of cards gives you different combinations every time
Mistakes in meiosis – number (nondisjunction – resulting in monosomy/trisomy) Refer to Table 4.2 p179.
- Nondisjunction: The failure of chromosomes to separate properly.
- Trisomy: inheriting one extra chromosome can result in various syndromes.
- Monosomy: inheriting one less chromosome.
What are the key events that occur at each stage of meiosis II?
…Meiosis II
1. Prophase II
- Sister chromatids condense and become visible, spindle fibers form, nuclear membrane disappears
2. Metaphase II
- Sister chromatids line up along the metaphase plate
- Spindle fibers attach at the centromere
3. Anaphase II
- Spindle fibers shorten and sister chromatids are pulled apart at the centromere and move to opposite poles of the cell.
4.Telophase II
- Spindle fibers disappear, nuclear membrane and nucleus reform
…Cytokinesis occurs
- End result is four haploid cells, each with n number of chromosomes
