1. meiosis SDL Flashcards
what is meiosis
a form of nuclear division occuring in germ cells (become gametes)
what is the difference between meiosis and mitosis
Mitosis produces two identical diploid cells and is involved in growth and maintenance, while meiosis produces four genetically diverse haploid cells and is involved in reproduction.
what are the phases of the cell cycle
mitotic
- prophase
- metaphase
- anaphase
- telophase
G1 phase
S phase
G2 phase
what are the phases oh mitosis
what occurs during the first meiotic division
DNA replication
- prophase 1
- metaphase 1
- anaphase 1
- telophase 1
what occurs during the second meiotic division
no DNA replication
- prophase 2
- metaphase 2
- anaphase 2
- telophase 2
what occurs during prophase 1
- nucleolus shrinks
- centroles migrate to opposite poles
- spindle forms (green, nucleus blue)
- chromosomes condense
- homologous chromosomes undergo synapsis and lie together to form a bivalent structure
- homologous chromosomes interlink
- chiasmata forms
what are the 5 stages of prophase 1
what occurs during metaphase 1
- Nuclear envelope disappears
- Homologous chromosomes move to equator of spindle (blue; spindle green)
- Centromeres of each bivalent chromosome orientate to opposite poles
what occurs during anaphase 1
- homologous chromosomes separate and migrate to opposite poles of the spindle
- one chromosome with 2 chromatids arrives at each pole
what occurs during telophase 1
- cytoplasmic division starts
- spindle breaks down
- nuclear envelope & nucleoli form
what occurs during prophase 2
- centrioles replicate & migrate to poles
- new spindle forms at right angles to previous one
- Non DNA replication!
what occurs during metaphase 2
- chromosomes move to the equator of the spindle
- chromatids orientate to opposite poles
what happens during anaphase 2
- chromatids separate and move apart to poles
what happens during telophase 2
- spindle disappears
- nuclear envelope & nucleoli form
- chromosomes become thread like
then cytoplasmic division
discuss spermatogenesis in terms of meiotic division
During spermatogenesis the primary spermatocyte in the testis undergoes the first meiotic division to form secondary spermatocytes which then undergo the 2nd division to form spermatids. Finally the spermatids differentiate into spermatozoa.
Meiosis 1: genetic diversity (crossing over)
Meiosis 2: hapoid gametes
[5 stages of meiotic prophase; pre-leptotene, leptotene, zygotene, pachytene and diplotene]
During oogenesis, the primary oocyte undergoes the first meiotic division to give a secondary oocyte and first polar body comtaining half the chromosomes. The secong meioic division then results in a single haploid ovum and a second polar body. So the polar bodies are packages of chromosomes that are not used any further and this is where oogenesis differs from spermatogenesis.
discuss meitoci division during oogenesis
through which methods does genetic variation occur to contribute to evolution
- independent assortment of chromosomes
- recombination
- mutation
how many mature gametes are produced from one complete meiotic division in oogenesis
one mature egg cell
discuss gene dosage compenation in females
list possible errors that can occur during meiosis
- somatic mutations can cause disease but cannot be passed to next generations
- germ line mutations can be passed on
- germ line mutations contribute to genetic variation but also can cause genetic disorders
- chromosomes can remain linked together leading to abnormal number of chromosomes
- aneuploidy results from the fertilization of gametes in which non-disjunction occured = abnormal number of a particular chromosome
chromosomal disorders effect fertility of cause disease
tortoise shell cats have which genetic defect
the result of an extra chromosome in a male, producing XXY individuals - meaning most of them are infertile (if they have XXY
At what stage do primary oocytes remain arrested until puberty?
prophase 1
