“Variable number of tandem repeats”; sequences repeated in tandem, but the number of repeats is different in different individuals. Unique regions constitute a locus, and define different alleles.
15,3 15,6 3,3 3,6
A cloned animal is obtained from an enucleated oocyte into which a diploid nucleus from a somatic cell has been inserted., then implanted. A live-born animal (sheep) would be a genetically identical clone of the nuclear donor cell.
A cloned gene/complete cDNA with a promoter and a poly(A) site is injected into a pro-nucleus of a fertilized zygote. The heterologous DNA is integrated into a chromosome of the host cell. Expressed in all cells or in only a few cells.
Interspersed repeats; a sequence short/long is present in many copies in the genome, which are inserted at random locations, in all or most chromosomes. The repeat number is also variable
It is most likely that the probe contains an interspersed repeat sequence, i.e. is not a purely unique DNA. The repeat sequence of the probe will hybridize to many different restriction fragments if the repeat is very abundant.
The child has three chr 18. One comes from the father (haplotype a), and the two others come from the mother. Since both haplotypes from the mother are found in the affected child, nondisjunction must have occurred in meiosis I in the mother.
What chromosomal abnormality would suggest that the risk of another Down’s syndrome child is considerable; matter where the karyotype was found?
There is X inactivation (for dosage compensation) in somatic cells, which is random in early embryogenesis. The retina of the female would have patches of cells with the normal X active (pigmented) and some with the chromosome silenced (not pigmented).
Alternatively, the segment of the X chromosome attached to the autosome might escape X inactivation. For a significant portion of the X chromosome there would thus be no dosage compensation, and this is also not compatible with normal development.