Chromosome Number Changes Flashcards
What are the common types of chromosome changes?
Translocation (from another chromosome)
Inversion (flipping of order of chromosome DNA sections)
Duplication
Extra chromosome [most are incompatible with life with few exceptions]
Missing chromosome (caused by non-disjunction) [incompatible with life for autosomes. Y chromosome missing is compatible with life though]
Deletion [Large deletions are incompatible with life]
What effect can inversion have on cells?
If regulatory sections are near different genes that can result in over-expression of the wrong genes (eg oncogenes)
What are the types of chromosome mutations?
Aneuploidy (number of chromosomes is altered)
Aberrant euploidy (Polyploidy, one or more complete sets of chromosomes are added/lost)
Chromosome rearrangements (alter the structure of chromosome)
What are the types of ploidy seen in human cells?
Haploid (one chromosome set)
Diploid (two chromosome set)
What are the different types of aneuploidy?
Nullisomy
Monosomy
Trisomy
Tetrasomy
How does aneuploidy take place?
Non-dysjunction results in paired chromosomes failing to separate during meiosis and migrate to the same daughter cell. This can occur at 1st or second meiotic division.
Are human autosomal monosomics viable?
No they die in utero. Some human autosomal trisomics are viable.
What is down’s syndrome’s aneuploidy?
Trisomy 21
Why is autosomal trisomy deadly usually?
Overexpression of genes by 50% more has dramatic consequences on cell function.
Altered gene balance
Altered gene ratio and product ratio
Change in phenotype
Expression of deleterious recessive alleles
What is the trisomy 21 phenotype?
Growth failure
Mental retardation
Flat back of the head
Abnormal ears
Many loops on fingertips
Broad flat face
Slanting eyes
Epicanthic eyefold
Short nose
Short and broad hands
Congenital heart disease
What is down’s syndrome’s incidence related to?
Maternal age, cause not verified.
Less pronounced link to paternal age but link still exists.
What are haplo-abnormal genes?
If only one copy of the gene is present it gives an abnormal phenotype.
What are triplo-abnormal genes?
If three copies of the gene are present this gives an abnormal phenotype
What is dosage compensation?
X chromosome’s housekeeping genes are expressed almost equally in males and females even though females have double the number of these genes.
Why does dosage compensation happen in females?
One of the 2 X chromosomes is switched off completely.
Females are mosaics and have some cells express genes from maternal X and other cells from paternal X.
