Chapter 12.2 - Sexual Reproduction Flashcards
Sexual Reproduction
- Two parents
- Each passes their genes to offspring
- Meiosis halves the chromosome number to produce gametes
- Fertilization involves the fusion of two gametes to restore original chromosome number
- Increases genetic variation
- 46 chromosomes > 2n/1 = 46 diploid and 23 haploid
Human Karyotypes
Homologous Chromosomes: Two chromosomes that look like one another, but they are not necessarily identical
Autosomes: Somatic Cells (44)
Allosomes: Sex chromosomes XX or XY
*we are diploids (2n = 46) but our gametes are haploid (n=23)
Meiosis 1 overview
- Replicate all chromosomes
- Crossing over occurs - homologous chromosomes exchange genetic information
- Chromosomes form tetrads - tetrads are chromosomes coming together
Meiosis 1 Order
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase 1 & Cytokinesis
- Metaphase II
- Anaphase II
Prophase 1
Each chromosome has replicated (sister chromatids). Crossing over occurs.
Metaphase 1
Chromosome pairs align at metaphase plate (tetrads). Random chromosome arrangements
Anaphase 1
Duplicated chromosomes of homologous pairs separate
Telophase 1 & Cytokinesis
Cytokinesis, followed by spindle formation
Metaphase II
Chromosomes align at metaphase plate and attach to spindle at the kinetochore
Anaphase II
Sister chromatids separate (random assortment). not genetically identical (crossing over)
3 causes of genetic variation in next generation
- Independent Assortment
- Chromatid Recombination
- Random Fertilization
Independent Assortment
- of chromosomes in Metaphase 1
* see two possibilities in notes*
Chromatid Recombination
see diagram in notes
Random Fertilization
- no crossing over for mitosis
- mitosis doesn’t have tetrads, the chromosomes line up in the metaphase plate
Why do the X and Y chromosomes pair during meiosis?
- The two are similar in genes (top and bottom of chromosomes)
- During tetrad formation, the regions that have genetic similarities interact where other parts do not.
- The X chromosome will bend to allow two parts to interact
- Y lost genes during evolution
