6.3 Meiosis Flashcards
What is a gamete?
haploid sex cells
produced by meiosis
in organisms which reproduce sexually
What is a diploid cell?
a cell containing the normal number of chromosomes
2 chromosomes of each type - 1 inherited from each parent
What is a haploid cell?
a cell containing half the normal number of **chromosomes**
formed by meiosis
1 chromosome of each type
What is meiosis?
form of cell division
where nucleus divides twice
resulting in halving chromosome number
& formation of 4 haploid cells from 1 diploid cell
What is a zygote?
initial diploid cell
when 2 gametes fuse
What are homologous chromosomes?
pair of chromosomes
containing same genes in corresponding loci.
1 inherited from each parent
What is an allele?
different versions of the same gene
How many chromatids are present in each chromosome of a diploid cell during G1?
1
What occurs during prophase I of meiosis?
- chromosomes condense
- nuclear envelope disintegrates
- nucleolus disappears
- spindle formation begins
Difference(s) to mitosis:
- as homologous chromosomes move through cytoplasm, crossing over occurs, where alleles are swapped leading to increased variation
What occurs during metaphase I of meiosis?
- Instead of chromosomes singly lining up at equator, bivalents line up at equator.
- orientation of maternal + paternal chromosome in homologous pair is random, which leads to increased variation >> independent assortment
What occurs during anaphase I of meiosis?
- instead of sister chromatids, homologous chromosomes are pulled to opposite poles
- entangled genes during crossing over break off & rejoin, thus swapping alleles & forming recombinant chromatids.
- points of breakoff = chiasmata
What occurs during telophase II of meiosis?
- nuclear membrane reforms
- chromosomes decondense
- cell undergoes cytokinesis & forms 4 haploid cells
How does metaphase II of meiosis differ to metaphase in mitosis?
although chromosomes singly line up at equator:
- sister chromatids are unidentical (due to crossing over)
- therefore independent assortment of sister chromatids can occur >> increased variation
How does anaphase II of meiosis differ from anaphase I?
instead of homologous chromosomes, sister chromatids are pulled to opposite poles
What 2 factors increase the variation between the genetic material of haploid cells?
- CROSSING OVER (during prophase I)
- INDEPENDENT ASSORTMENT (during metaphase I + II)
Which stage of meiosis is considered reduction division & why?
Meiosis I
due to decrease in chromosome number
(disregard number of chromatids in each chromosome)
