Chapter 2 Flashcards
Meiosis
Formation of gametes in which the number of chromosomes is reduced
Fertilization
Two haploid gametes fuse and restore the number of chromosomes to its original diploid value
What are the five stages of prophase I
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis
Leptotene
Chromosomes condense and become visible
Zygotene
Chromosomes continue to condense, homologous chromosomes pair up and begin synapse – a close association
Homologous pairs come together to form a synapse
Bivalent/Tetrad
Each homologous pair of chromosomes, 2 chromosomes and 4 sister chromatids
Pachytene
Chromosomes become shorter and thicker, and a three-part synaptonemal complex develops between homologous chromosomes
A protein between the two chromosomes form
Crossing Over
In which homologous chromosomes exchange genetic information
Intra - chromosomal recombination
Chiasma
The location where two chromosomes cross over
Diplotene
The centromeres of the two homologous chromosomes move apart
Diakinesis
Chromosome condensation continues…the nuclear membrane breaks down
Metaphase I
Homologous chromosomes align up on the metaphase plate
Anaphase I
Homologous chromosomes move apart – the sister chromatids remain attached
Telophase I
The chromosomes arrive at the spindle poles, and the cytoplasm divides – interkinesis
Interkinesis
The nuclear membrane reforms around the chromosomes clustered at each pole, the spindle apparatus breaks apart, and the chromosomes relax
Prophase II
The events of interkinesis are reversed
Metaphase II
sister chromatids align on the metaphase plate
Anaphase II
The sister chromatids separate
Telophase II
The chromosomes arrive at the spindle poles, a nuclear membrane reforms around the chromosomes and the cytoplasm divides – cytokinesis
chromosome become no longer visible
What causes genetic variation?
- Crossing Over in Prophase I
- Random separation of homologous chromosomes in Metaphase I
What evidence from yeast relay about crossing over?
Crossing over starts from zygotene and ends until the end of Prophase I
Intra-chromosomal Recombination
The creation of new combinations of alleles on a chromatid
Cohesins
They control the segregation or the separation of homologous chromosomes during mitosis and meiosis
- protein rings
What holds homologous chromosomes together?
Cohesins along the chromosome arm hold homologs together
