Chapter 4b: Variations in Genome Structure: Changes in Chromosome Structure Flashcards
chromosomal aberrations
a. deletions
b. duplications
c. inversions
d. Reciprocal Translocation
Alterations in the number of genes
deletions and duplications
Alterations in the location of genes
inversions and translocations
loss of a chromosomal segment; could be homozygous or heterozygous
deletions
Genetic Effects of Deletion
- lethal in the homozygous and hemizygous condition
- reduced viability
- modified phenotypic ratio
Term for the expression of a normally recessive trait due to the loss of the corresponding dominant allele?
pseudo-dominance
syndrome due to a deletion in the short arm of chromosome # 5
Cri du chat syndrome
Chromosome 7 loses an end piece
- Turned up nose
- Wide mouth with small chin
- Poor academic skills but well developed verbal and musical skills
- ‘elfin’ facial appearance
Williams syndrome
due to a repeated portion in a chromosome due to unequal crossing over or errors in replication
Duplications
Genetic effects of duplications
gene redundancy
occur when parts of chromosomes become detached, turn through 180 degrees and reinserted in such a way that the genes are in reversed order.
inversions
arise from chromosome entanglements and breakages during meiotic prophase; also from recombination between transposable elements
inversions
Cause linear rearrangement of genes in a chromosome
inversions
In inversion heterozygotes, a __ forms from the pairing of the inverted and non-inverted regions
loop
two types of inversions
- pericentric inversion
- paracentric inversion
inversion that is situated in a chromosome arm to one side off the centromere
paracentric inversion
A child with __, dicentric chromosome 15 arising from a maternal paracentric inversion of chromosome 15q
bisatellited
Tobiano color pattern is due to a large __ on Equus caballus chromosome 3 (ECA3), which may alter the expression of the KIT receptor tyrosine kinase.
inversion
*Involves interchange of blocks of genes between two
nonhomologous chromosomes
reciprocal translocation
- linkage relationships between genes change
reciprocal translocation
*Translocation heterozygotes exhibit the characteristic __ during meiotic prophase due to the pairing of homologous chromosome parts
cross-like configuration
types of reciprocal translocation
- alternate
- adjacent 1
- adjacent 2
type of translocation
- the breaks occur at different points on the chromosomes involved, and the segments are exchanged between non-homologous chromosomes.
- does not directly involve the centromeres of the chromosomes.
- The result is two derivative chromosomes, each carrying a combination of genetic material from the two original chromosomes.
- typically do not lead to significant genetic disorders unless crucial genes are disrupted or gene expression is altered.
alternate translocation
- typically involves acrocentric chromosomes
- the long arms of two acrocentric chromosomes break near the centromere, and the long arms fuse, while the short arms are lost.
- results in one large chromosome with the combined genetic material of the two original long arms, and another small chromosome consisting of the fused short arms.
Adjacent 1 Translocation (Robertsonian Translocation)
- breaks on both chromosomes adjacent to the centromere, leading to the exchange of terminal segments between the chromosomes.
- involve the centromeres of the chromosomes
Adjacent 2 Translocation
In __ a translocation places the c-myc protooncogene in the vicinity of the immunoglobulin heavy chain enhancer. This causes overproduction of c-myc.
Burkitt’s lymphoma
a mutated gene that has the potential to cause cancer.
oncogene
reciprocal translocation between chromosomes 2 and 22 causes
Alagille Syndrome
- Found in leukocytes of patients with chronic myeloid leukemia and other types of leukemia.
- reciprocal translocation in chromosome 9 and 22
Philadelphia chromosome
