Meiosis Flashcards
What is meiosis?
Meiosis is a type of cell division that occurs in the reproductive organs to form gametes, producing four daughter cells with half the number of chromosomes (haploid).
Why is meiosis important in sexual reproduction?
It ensures that gametes have half the chromosome number so that, after fertilization, the zygote has the correct diploid number.
What is the diploid number of chromosomes in humans?
46 chromosomes (2n), found in body cells.
What is the haploid number of chromosomes in humans?
23 chromosomes (n), found in gametes.
What happens when a sperm and egg fuse?
Their haploid chromosomes combine to form a diploid zygote with 46 chromosomes.
What happens during Meiosis I?
Homologous chromosomes pair, crossing over occurs, and homologous pairs separate into two cells (haploid), each with chromosomes made of two chromatids.
What is crossing over and when does it happen?
The random exchange of genetic material between chromatids of homologous chromosomes during Prophase I.
What happens during Meiosis II?
The two haploid cells divide again; this time chromatids separate, resulting in four genetically different haploid cells.
What happens in Metaphase I?
Homologous chromosome pairs align randomly along the equator of the cell.
What happens in Anaphase I?
Homologous chromosomes (not chromatids) are pulled to opposite poles.
What happens in Metaphase II?
Chromosomes line up again, but now in haploid cells.
What happens in Anaphase II?
Chromatids are pulled apart to opposite poles.
What is the end result of meiosis?
Four non-identical haploid cells (gametes), each with different genetic combinations.
In which cells does mitosis occur?
Somatic (body) cells.
In which cells does meiosis occur?
Reproductive cells (ovaries and testes).
How many daughter cells are produced in mitosis vs meiosis?
Mitosis: 2 identical diploid cells. Meiosis: 4 different haploid cells.
Does crossing over occur in mitosis?
No, only in meiosis during Prophase I.
Do homologous chromosomes pair up in mitosis?
No, they only pair in meiosis.
How does meiosis cause genetic variation?
Through crossing over and random assortment of chromosomes during metaphase stages.
Why is genetic variation important?
It increases the chances that some individuals in a species can survive changes in the environment.
How are inheritable characteristics transmitted?
Through gametes formed during meiosis; offspring receive genetic material from both parents.
How does meiosis contribute to evolution?
Meiosis creates variation in gametes; natural selection acts on these variations, leading to evolution over generations.
How does Darwin’s theory relate to meiosis?
It explains that variations from meiosis result in some offspring being better adapted to survive and reproduce, driving evolution.
Define ‘homologous chromosomes’.
A pair of chromosomes—one from each parent—that are the same size and shape and carry genes for the same traits.
