Meoisis

Frage	Antworten
What is meiosis?	Process by which sex cells are made in the reproductive organs. It is the reduction division of a diploid nucleus to form a haploid nucleus.
What type of nucleus do most sexually reproducing animals have?	Diploid - they have two copies of every chromosome (one maternal, one paternal)
In order to reproduce, what do organisms need to do?	Make gametes that are haploid
What will the fertilisation of two haploid gametes result in?	The formation of a diploid zygote that will grow into a new organism
What does meiosis consist of?	Two cell division: First division - reduction division of diploid nucleus to form haploid nuclei Second division - separates sister chromatids
Define homologous chromosomes	Chromosomes that share the same structural features and the same genes at the same loci position
Name three structural features	Size, banding pattern, centromere position
What does non-disjunction refer to?	Chromosomes failing to separate correctly, resulting in gametes with one extra or missing chromosome
What can non-disjunction lead to?	Change in chromosome number?
Ways of chromosomes failing to separate	During Anaphase I - resulting in four affected daughter cells During Anaphase II - resulting in two affected daughter cells
Example of non-disjunction	Down Syndrome - Trisomy 21
How does Down Syndrome occur?	One of the paternal gametes had two copies of chromosome 21 as a result of non-disjunction The other paternal gamete was normal and had a single copy of chromosome 21 When the two gametes are fused during fertilisation, the resulting zygote had three copies of chromosome 21.
What is karyotyping?	A method of visually profiling all the chromosomes in a cell
How are chromosomes arranged in karyotyping?	In homologous pairs according to their structural characteristics
How is karyotyping performed?	Harvesting cells from foetus or white blood cells of adults Chemically inducing cell division, then halting it during mitosis when chromosomes are condensed and thus visible (this stage determines whether they appear as sister chromatids Staining and photographing chromosomes, before arranging them according to structure
Why is prenatal karyotyping used?	Determine the gender of an unborn child Test for chromosomal abnormalities
How are cells collected for karyotyping for pre-natal diagnosis?	Chorionic villus sampling or amniocentesis.
Describe the process of amniocentesis	A needle is inserted through the abdominal wall, into the amniotic cavity in the uterus and a sample of amniotic fluid containing foetal cells is taken. It can be done from the 16th week of pregnancy with a slight chance of miscarriage.
Describe the process of Chronic Villus Sampling	A tube is inserted through the cervix and a tiny sample of the chorionic villi form the placenta is taken. It can be done from the 11th week of pregnancy with a slight chance of inducing miscarriage.
What is aneuploidy?	Abnormal number of chromosomes

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