Chromosomal Abnormalities

cytogeneticist

a scientist who studies variations in chromosome structure and number

karyotype

a micrograph that arranges chromosomes with the short arm (p arm) at the top and then descending order by size

metacentric chromosome

centromere in the middle

submetacentric chromosome

slightly off center centromere

acrocentric chromosome

centromere is near one end

telocentric chromosome

centromere at the bottom/top

giemsa stain

a nucleic acid stain that reveals the g banding pattern

g banding

the black and white banding patterns made through staining - used to distinguish chromosomes

g-bands

regions rich with adenine and thymine that are gene poor - bind more stain and appear darker; are also heterochromatic

heterochromatic

different or other chormatin - more tightly packaged

euchromatic

less condensed chromatin

light bands

rich with guanine and cytosine, gene heavy - incorporates less giemsa stain; lighter bands

What is the banding pattern used for?

1. distinguishes individual chromosomes from each other
2. detects changes in chromosome structure
3. reveals evolutionary relationships among chromosomes of closely related species

deficiency (or deletion)

the loss of a chromosomal segment

duplication

the repetition of a chromosomal segment compared to the normal parent chromosome

inversion

a change in the direction of part of the genetic material along a single chromosome - pericentric and paracentric

pericentric inversion

the centromere is found within the inverted region

paracentric

the inverted section is on the p or q arm and doesn't involve the centromere

translocation

a segment of one chromosome becomes attached to a different chromosome

simple translocation

- one way transfer
- a piece of a chromosome is attached to another chromosome

reciprocal translocation

- two way transfer
- two different types of chromosomes exchanged pieces, producing two abnormal chromosomes with translocations (not crossing over)

Are duplications or deletions more harmful?

deletions - few syndromes are caused by small chromosomal duplications

what issues can chromosomal duplications cause?

they can lead to problems with the synaptonemal complex when it forms during meiosis - exacerbating problems in future offspring

why are chromosomal duplications important?

they provide the raw material for the addition of genes to a species

gene families

consists of two or more genes derived from the same ancestral gene

homologs

two or more genes derived from a common ancestor

paralogs

homologous genes in the same species due to duplication (common ancestry, different functions)

orthologs

homologous genes that are in different species changed by speciation (still common ancestry but different functions)

copy number variation (CNV)

when a particular number of copies of a particular gene varies from one individual to the next
- may have less copies due to deletion
- may have more due to duplication

combined dna index system (CODIS)

the USA's national dna database created and maintained by the FBI

short tandem repeats (STRs)

a type of CNV where a sequence of nucleotide base pairs that are repeated over and over again
- at each location tested - locus - a person has two sets of repeats, one from each parent

breakpoint effect (from inversion)

an inversion break point that occurs in a vital gene

position effect (from inversion)

a gene is re-positioned in a way that alters its gene expression (over or under produced) and thus influences individuals phenotype

inversion heterozygotes

people who carry one inverted and one normal chromosome

unbalanced translocation

a translocation in which a cell has too much genetic material compared with a normal cell - likely to cause chromosomal abnormalities like down syndrome

euploid

the normal number of chromosomes - 2n

aneuploidy

abnormal number of chromosomes

non disjunction

failure of a chromosome to separate during anaphase I or anaphase II

monosomy

the loss of a single chromosome; chromosomal composition is 2n-1

trisomy

the gain of an extra copy of a chromosome; chromosomal composition is 2n+1

barr body

an unactive x chromosome that is tightly packaged so 85% of it can't be used

Klinefleter syndrome

(XXY) limited testosterone, often sterile

triple x females

xxx - an extra barr body but still produces 15% too much protein

turner syndrome

x - 15% too little x chromosome protein

down syndrome

extra 21st chromosome

edwards syndrome

extra 18th chromsome

cri-du-chat syndrome

part of p-arm on chromosome missing

jacobs syndrome

xxy

patau syndrome

extra 13th chromsome

myoglobin

stores oxygen in muscle cells

hemoglobins

bind and transport oxygen via red blood cells