lesson 1: Meiosis Flashcards
What is sexual reproduction?
A process involving the mixing of DNA to create a new combination of genes
What are the types of cells in humans regarding ploidy?
- Somatic cells: 2n (diploid)
- Gametes: n (haploid)
- Zygote: 2n (diploid)
What does sexual reproduction imply about cell types?
Alternation of haploid and diploid cells
What is the first step in sexual reproduction?
Meiosis
How do gametes form?
They are formed by meiosis of germ cells (2n)
How does meiosis differ from mitosis?
- 2 consecutive divisions
- 1 parent cell (2n) produces 4 daughter cells (n)
- Daughter cells are different from one another and from the parent cell
What occurs during Prophase I of meiosis?
- Chromatin condenses into X-shaped chromosomes
- DNA replicates
- Homologous chromosomes pair up
What is synapsis in meiosis?
- The pairing and binding of homologous chromosomes by the synaptonemal complex
- happens in prophase 1 of meiosis 1
What is a bivalent in meiosis?
A group of 4 sister chromatids in paired homologous chromosomes
What happens during the Pachytene stage of Prophase I?
- 3rd out of 5 stage
- Crossing over/recombination occurs: chromatids from each homologous chromose exchange segmenets of alleles
What are alleles?
Different versions of the same gene on each homologous chromosome
What occurs during Diakinesis stage of Prophase I?
- last stage
- Nuclear membrane disappears
- Centrioles move to opposite sides
- Spindle fibers fan out
What happens during Metaphase I?
Homologous chromosomes line up at the equator and attach to spindle fibers
What occurs during Anaphase I?
Spindle fibers separate the homologous chromosomes and pull them to opposite poles
What is produced at Telophase I?
- One chromosome from each homologous pair at separate poles
- Nuclear fibers disappear
- Nuclear membrane reforms around the chromosomes
- Cytokinesis: 2 genetically different haploid daughter cells
- Each haploid cell contains only one set of chromosomes
What happens during Prophase II?
Nuclear membrane disappears and spindle fibers fan out
What occurs in Anaphase II?
- Sister chromatids separate and move to opposite poles
- once sister chromatids speerate they are called chromosomes
What happens in Telophase II?
Spindle fibers disappear
Nuclear membrane reforms
Cytokinesis occurs in both cells which causes 4 genetically different haploid daughter cells
What is gametogenesis?
The process of forming gametes (n) from germ cells (2n)
What are the two types of gametogenesis?
- Spermatogenesis
- Oogenesis
What occurs during oogenesis before birth?
Female babies start making oocytes which pause in Prophase I
What happens to oocytes after puberty?
They resume division, completing Meiosis I and forming Oocyte II
What triggers the completion of Meiosis II in oocytes?
Fertilization by sperm
What is the result of spermatogenesis?
4 sperm cells per spermatocyte I
