BISC 200: Chromosome Mutations

Exam 2

aneuploidy

an organism gains or loses one or more chromosomes, NOT a complete set

monosomy

loss of a single chromosome

trisomy

gain of one chromosome

euploidy

has one complete set of chromosomes

polyploidy

more than two copies are present

nondisjunction

failure of chromosomes to separate in gametes (generally the source of aneuploidy)

Klinefelter Syndrome

gain of an X chromosome (47, XXY)

Turner Syndrome

loss of an X chromosome (45,X)

Cri du chat syndrome

monosomy

Trisomy 21 (Down Syndrome)

the only autosomal trisomy that allows for survival into adulthood

most common cause is through nondisjunction, 21+

mosaicism

two or more populations of cell lines that are different

how translocations can cause Down Syndrome

a part of the extra chromosome at 21 breaks off and joins 14

polyploidy general facts

based on the number of sets of chromosomes; can be due to errors in meiosis during gamete formation, events that occur after fertilization, errors in mitosis after fertilization

deletion

a mutation where part of a chromosome is deleted

terminal deletion

deletion occurs on the end of the chromosome

intercalary deletion

deletion occurs within the chromosome (the middle)

what can cause deletions?

can be random or when the chromosome is exposed to agents (heat, radiation, chemicals, viruses)

example of a condition caused by deletions:

Cri du chat syndrome

acentric chromosome

a chromosome fragment with no centromere (leads to loss of entire chromosome)

compensation loop (deficiency or deletion loop)

part of the chromosome that breaks and is lost

duplication

can arise due to unequal crossing over events between synapsed chromosomes during meiosis

ex: isodicentric 15

three aspects of duplications

gene redundancy, may produce phenotypic variation, source of genetic variability during evolution

inversion

mutation where a segment is removed and reintroduced 180 degrees from the original orientation

two types of inversions and their definitions

pericentric - includes the centromere (more common)

paracentric - doesn’t include the centromere

translocation

mutation in which there is a change in position of chromosome segments and the gene sequences they contain to a different location in the genome

different types of translocations and their definitions

Robertsonian translocation (centric fusing) – most commonly seen in humans; chromosome breaks at centromeres, and long arms fuse to form one long chromosome

Reciprocal - segments of chromosomes are exchanged between two different chromosomes (two like chromosomes is crossing over)

what is an example of translocation

chronic myelogenous leukemia - converts proto-oncogenes to oncogenes

proto-oncogene

gene that functions to control normal proliferation of cells (normal cell division)

oncogene

gene that promotes unregulated cell proliferation

familial down syndrome

example of centric fusion; translocation typically impacts the products of meiosis (gametes)

fragile sites (fragile X syndrome)

associated with a form of mental disabilities (at the end of chromosomes), associated with the chromatin fibers that are not tightly coiled

X-syndrome – X-chromosome long arm is prone to breaking

Trinucleotide repeats – (CGG) sequence of three nucleotides that repeats; more repeats = more severe symptoms