3.3 Flashcards
What are gametes?
Sex cells, like egg, sperm, or pollen
What is meiosis?
Meiosis is the cell division process that is used to produce cells that have a reduced number of chromosomes by dividing twice, but only copying DNA once.
Why do gametes undergo meiosis?
Gamete must have a haploid (half) number of chromosomes, so they can’t use mitosis
Why does mitosis (2n) produce diploid, daughter cells and meiosis produce haploid (n) daughter cells?
In meiosis, the DNA is copied once, but the cell divides twice
When is DNA replicated when meiosis is used?
Whilst the chromosomes formed during prophase, DNA is replicated prior to that during interphase
What is the order of stages in meiosis?
Interphase
Prophase one
Metaphase one
Anaphase one
Telophase one
Prophase, two
Metaphase, two
Anaphase, two
Telophase, two
When does crossing over occur?
During prophase one
How does crossing over occur?
A pair of homologous chromosomes line up next to each other
Parts of the chromosomes are exchanged between the maternal and paternal pairs
Why are the same genes exchanged during crossing over?
Because the chromosomes break and reattach at the same locus
Is crossing over random or a set process
Crossing over is a random process
What does crossing over result in?
The recombination of genetic material
What is the chiasma?
The location on the chromosome, where Crossing over occurs
What occurs during metaphase one?
The chromosomes lineup in the middle of the cell, still in the homologous pairs, the way that they lineup is completely random
What happens during the different phases of interphase?
Growth occurs in G1
DNA replication occurs in the S phase
Preparation for division occurs in G2
Why are siblings, not identical?
Because each gamete is genetically unique. This is caused by crossing over and random variation of homologous, chromosome’s during metaphase, one, and two
What is fertilisation?
The fusion of to haploid gametes to form a diploid zygote
When does non-disjunction occur?
During meiosis, when chromosomes don’t separate properly during anaphase, one or two
What is the name syndrome that results from non-disjunction?
Trisomy, 21 or down syndrome is characterised by stunted growth, low muscle tone and characteristics facial features and mental impairment
Where can the cells for Karyo typing be obtained?
There are two methods
1. Aminocentesis: a needle is inserted into that amniotic sac to pull out some of the amniotic fluid containing fetal cells.
2. Chronic villus sampling: inserting a needle into the placenta, which contains fetal cells
Why does down syndrome incidents increase with maternal age?
Because the oocytes are getting older
