What is it called when homologous chromosomes fail to separate properly?
Meiosis 1 disjunction
Meiosis 2 disjunction
Precocious sister chromatid separation
The following shows the sister chromatids failing to separate during Meiosis 2- aka Precocious sister chromatid separation
Of the four gametes, 2 of one pair are normal, and of the other pair one is disomic and the other is nullosomic- what has gone wrong?
Meiosis II Non-disjunction
Meiosis I disjunction
What is different about Meiosis II non-disjunction and Precocious sister chromatid separation?
In MII, the nullosomic and disomic gametes occur from the same cell In PSCS, the nullosomic and disomic gametes occur from different cells
In PSCS, the nullosomic and disomic gametes occur from the same cell In MII, the nullosomic and disomic gametes occur from different cells
Aneuploidy- an abnormality of chromosome number where the number of chromosomes present is not a multiple of the haploid number
Nullosomy- where one of the chromosomes is lost (2n-1)
Monosomy is universally lethal to humans embryo's
Which of the following is fatal in animals but not always in plants
Nullosomy
Trisomy
Monosomy
Trisomy's of some chromosomes are survivable in humans
Down's Syndrome is caused by trisomy of which chromosomes?
21
18
13
Down's Syndrom is present in 1/750 babies
Which of the following are potentially symptoms of Down's Syndrome?
Abnormal fingerprints
Congenital heart disease
Gigantism
Intellectual disability
Webbed fingers
Trisomy 18 is Ptau's syndrome and is found in 1/6000 births
Which of the following are potentially symptoms of Edwards syndrome?
Rockerbottom/clubbed feet
Muscle rigidity
Ptau's Syndrome is the most common, present in 1/200 births
List the potential symptoms of Ptau's syndrome
Clubbed/rocker bottom feet
Post axial polydactyly
Cleft lip/palate
In fetus' with Ptau's Syndrome, there are 100x more spontaneous abortions/lost pregnancies that stillbirths
When distinguishing between types of mis-segregation, what is required for direct assessment of genetic markers (ideally)?
Allele- specific PCR.
Genetic information from siblings
Genetic offspring from a parent
Genetic offspring from both parents
Genetic offspring from grandparents
90% of aneuploidy's are caused by the sperm, not the egg
Define Pleiotropy
Where mutation in a single gene only causes a change in a single trait
Where mutation in a single gene can cause multiple, seemingly unrelated phenotypes
Aneuploidy effects entire chromosomes, and so its effects are always Pleiotropic
A phenotype associated with a pleiotrophic gene may show greater expressivity than another phenotype associated with the same gene
Match the following Trisomies with the problematic chiasmata in the Maternal Meiosis diagram
Top- 16 (proximal) Mid- 18 (achiasmate) Bot- 21 (achiasmate, proximal, distal)
Top- 21 (proximal) Mid- 18 (achiasmate) Bot- 16 (achiasmate, proximal, distal)
Top- 18 (proximal) Mid- 16 (achiasmate) Bot- 21 (achiasmate, proximal, distal)
Without crossover, only 40% of homologous chromosomes align correctly
Define the Chiasma hypothesis
Chiasma make the cell more vulnerable to aneuploidy
Without crossover, cells become more vulnerable to aneuploidy
Silkworm females and male sloths pair each side of the synaptonemal complex with no crossing over
Once produced, how are oocytes stored in the uterus and for how long?
As bivalents
As a synaptonemal complex
3-5 weeks
3-5 years
10-50 years
The way oocytes are stored is known as Dictyate Arrest
What makes the continued arrestment of oocytes in bivalent form difficult?
Cohesin is lost as cells age
DNA begins to degenerage if held in bivalent form too long
Bivalents held together too long will bind too tight to be unwound
List the three things that can happen in an aging oocyte
The bivalent cannot be broken
The DNA begins to degrade
There is precocious loss of centromere cohesin in Meiosis I
There is Precocious Separation of sister chromatids
A univalent is formed
During dictyate arrest, achiasmate segregation factors can deplete