18. Behaviour of chromosomes and alleles Flashcards
Define autosome
A chromosome not involved in determining the sex of the organism
Karyogram
A drawing of chromosomes with banding shown.
According to what features are chromosomes sorted?
- size
* centromere position
Aneuploidy
Lose 1 or 2 (less than one whole set)
Euploidy
When an organism has one or more than one complete set of chromosome
Polyploidy
When a cell or organism has more than two paired (homologous) sets of chromosomes.
- ie. triploidy (2 sets of chromosomes)
Klinefelter syndrome
XXY
- sex chromosome aneuploidy
Aneuploidy
plus or minus a chromosome (or a few - but less than a set)
Which is worse; an extra chromosome or extra autosome?
Extra autosome can be lethal
Why does having an extra autosome have adverse affects while an extra sex chromosome can be tolerated?
- genetic imbalance caused by genes on autosome can be lethal
- affects of an additional X chromosome may be reduced by x-inactivation
- Y chromosome does not contain many genes
Phenotype (affects) of klinefelter syndrome
- small testes
- reduced testosterone
- delayed or incomplete puberty
- breast enlargement
- reduced facial/body hair
- infertility
What is the relation between the incidence of trisomy 21 and maternal age?
As maternal age increases, incidence of trisomy 21 increases
Why is the chance of chromosomal problems higher as age of mother increases?
Older eggs are significantly more likely to have abnormally functioning spindles - which causes an increased rate of chromosomal problems in the mature egegs
What is translocation in chromosomes?
Translocation is a type of chromosomal abnormality in which a chromosome breaks and a portion of it reattaches to a different chromosome
What is non-disjunction?
The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.
What is meant by acrocentric (chromosomes)?
- A chromosome in which the centromere is located quite near one end of the chromosome.
- Humans normally have five pairs of acrocentric chromosomes.
What tests are carried out to detect chromosomal disorders in pregnancy?
- preimplantation diagnosis (PGD - with IVF)
- ultrasound
- triple test of maternal blood
- Chorionic villus sampling
- amniocentesis
What are the three specific substances in a triple test of maternal blood?
- AFP
- hCG
- Oestriol
What is AFP in triple test of maternal blood?
Alpha-fetoprotein
• protein that is produced by the fetus
• high - indicator of neural tube defect
What is hCG in triple test of maternal blood?
human chorionic gonadotropin
• a hormone produced within the placenta
What is Oestriol in triple test of maternal blood?
Oestriol is an estrogen produced by both the fetus and the placenta
How is cf DNA in maternal blood used to detect chromosomal abnormalities?
- cell-free (cDNA) are short DNA fragments
- cfDNA in maternal blood comes from both mother and fetus
- in trisomy 21 the amount of cDNA for chromosome 21 is higher than in normal pregnancies
Disadvantage of chorionic villus sampling and amniocentesis?
Chorionic villus sampling and amniocentesis is invasive
Define monohybrid cross
A monohybrid cross is a genetic mix between two individuals who have homozygous genotypes (completely dominant or completely recessive alleles)
•inheritance of a single trait
