Chapter 3- Genetics- Meosis Flashcards
(State that meiosis is a reduction division of diploid nucleus to form haploid nuclei:)
Most sexually reproducing animals are diploid which means?
They have to copies of every 2 copies of every chromosome (one maternal origin one paternal)
(State that meiosis is a reduction division of diploid nucleus to form haploid nuclei:)
-what is the process of meiosis?
Process by which sex cells (gametes) are made in the reproductive organ
(State that meiosis is a reduction division of diploid nucleus to form haploid nuclei:)
In order to reproduce organisms need gametes that are?
Haploid (have only one copy of each chromosome)
(State that meiosis is a reduction division of diploid nucleus to form haploid nuclei:
The fertilisation of 2 gametes results in?
Formation of a diploid zygote
(State that meiosis is a reduction division of diploid nucleus to form haploid nuclei:)
Meosis consists of 2 cell divisions what are they?
1st division= reduction devision of the diploid nucleus to form haploid nucleus
2nd division= separates sister chromatids
What do homologous chromatids share?
The same structural feature. (Eg size, pattern)
The same genes at the same loci positions (genes= some alleles might be different)
How many cells does Meosis produce?
4
What is the 1st stage of Meosis?
‘S’ phase of interphase- DNA replication
Why does DNA replication occur in the first stage of Meosis?
To make a copy of its genetic information during interphase–> results in each chromatid having an identical copy or sister chromatid attach to it at the centromere
Draw the crossing over diagram in Meosis
Fucking do it you have a week.
What 4 things happens in prophase 1?
1) chromosomes become visible as DNA compacts (super coiling)
2) homologous chromosomes are attracted to each other and pair up–> one from father, one from mother
3) crossing over occurs between non-sister chromatids
4) spindle fibres made from microtubles form
What 2 things happens in metaphase 1
1) bivalents (another name for homologous pairs of chromosomes) line up across cell equator
2) nuclear membrane disintegrates
What 1 thing happens in anaphase 1?
1) spindle fibres from the poles attach to chromosomes and pull them to opposite poles of the cell
What 2 things happen in telophase 1?
1) spindles and spindle fibres disintegrate
2) usually the chromosomes uncool and new nuclear membrane forms
What happens at the end of Meosis 1?
Cytokines
What happens in cytokines 1?
Cell split into 2 separate cells
Cells=haploid because only contain 1 chromosome of each pair
Now Meosis 2 can take place in order to separate sister chromatids
What 2 things happens in prophase 2?
1) DNA condenses into visible chromosomes again
2) new meiotic spindle fibres are produced
What 3 things happen in metaphase 2?
1) nuclear membrane disintegrates
2) individual chromosomes line up along the equator of each cell, in random orientation
3) spindle fibres from opposite poles attach to each of the sister chromatids at the centromere
What 4 things happen in anaphase 2?
1) centromeres of each chromosomes splits, releasing each sister chromatid
2) spindle fibres pull individual chromatids to opposite ends of cell
3) because of the Radom orientation- chromatids coul be pulled towards either of the newly forming daughter cells
4) 2^23 possibilities
What 2 things happen in telophase 2?
1) chromosomes unwind their strands of DNA
2) nuclear envelopes form around each of the 4 haploid cells preparing them for cytokines
Definition of non-disjunction
Chromosomes failing to separate properly resulting in extra gametes 1 or 1 missing (aneuploidy)
How may non-disjunction occur? And how does it affect daughter cells?
- failure of homologous to separate during anaphase 1 resulting in 4 Affected daughter cells
- failure of sister chromatids to separate during anaphase 2 affecting 2 daughter cells
3 copies of chromosome 21 (trisomy 21) means?
Makes Down syndrome
Give an example of how parents can result in a child having 3 chromosomes 21
One parents gametes has 2 copies of chromosome 21 as a result of non-disjunction the other parent has 1 copy of chromosome 21 and when fusedd together zygote has 3 copies of chromosome 21
In karyotyping how are chromosomes arranged?
Arranged into homologous pairs and displayed according to their structural characteristics and go down in size
How are chromosomes able to be seen in karyotyping?
Involves harvesting cells (usually from foetus or white blood cells of adult) and chemically inducing cell division but stopping it dying meiosis when chromosomes are condensed and visible they are then stained and photographed before arranging them into structure
What is karyotyping tend to be used for?
Determine sex of child
Test for chromosomal abnormalities
What are the 2 ways of getting chromosomes with karyotyping?
Amniocentesis and chorionic villus sampling
What happens during Amniocentesis?
Needle inserted through abdominal wall into amniotic cavity in the uterus and a sample of amniotic fluid containing foetal cells is taking
How far in the pregnancy can amniocentesis happen? And what is the chance of miscarriage?
16th week
~0.5%
What happens in chorionic villus sampling?
Tube is inserted through the cervix and a tiny sample of chorionic villi (contains foetal cells) from placenta is taken
What chromosomes show a male/female?
What shows if it has Down syndrome?
Male= X Y female= X X
Down syndrome= 21sr chromosome has 3
