
Nuclear Genes
o Heterochromatin and centromeric regions are non-coding
 Chromosome 4 and 18 are gene poor
o Sub-telomeric regions are euchromatin, coding
 Chromosome 19 and 22 are gene rich
o Multigene family: code for proteins of similar function
 Classic: show high degree of DNA sequence similarity
 Gene superfamily: have limited sequence homology but are functionally
related having similar structural domains
o Pseudogene: similar to expressed gene but not generally expressed
 Duplication event but inactive d/t mutations is regulatory elements
 Insertion of cDNA sequence without promotion sequences of expression
o Extrageneic DNA: originally thought to be“junk DNA” not attributed to
function
 miRNA: repress gene expression through RNA/DNA hybrid
 tandem repeats
 satellite DNA: repeats around centromere
 mini-satellite: telomeric portions and hypervariable short tandem
repeats (used for DNA fingerprinting)
 microsatellite: very short repeats throughout genome, usually
associated with disease ( used for paternity and forensic analysis)

interspersed repetitive sequence:
 short interspersed nuclear elements (SINEs): ALU repeats used as
restriction site and can generate transposons
 long interspersed nuclear elements (LINEs): encode for reverse
transcriptase
 **Both LINEs and SINEs are implicated in inherited disease**

Mitochondrial DNA (mtDNA)
o Encodes 37 genes
 rRNA
 22 tRNAs
 13 subunits of enzymes (think ETC)
o mtDNA is maternally inherited

Cytogenics: study of chromosomes and cell division
o During division chromosome features are most evident
 Sister chromatids: two identical DNA strands
 Centromere (with p-petite and q- grande arms)
 Kinetochore: proteins that assemble at centromere for microtubule
attachment
 Microtubule: tubulins, motor proteins (dynein and kinesin)
 Telomere: seals end of chromosome, maintains integrity
 Chromosome classification (based on centromere location)
 Metcentric: located near center
 Submetacentric: intermediate position
 Acrocentric: at terminal ends

Chromosomal complement
 22 autosomes and one pair of sex chromosomes= 46 diploid
number
 One member of each pair derived from each parent= 23 haploid
number
 Members of chromosome pair= homolog

Chromosome nomenclature
 A given point (or gene location) identified by:
o chromosome number: 1-22
o chromosome arm: p or q
o Chromosome band: 1-X

Stages of the Cell Cycle
o Interphase
 G1: growth
 S: synthesis
 G2: error fixes
o Mitosis: chromosome and nuclear division
 Prophase: centrioles form, chromosomes condense, nuclear membrane
degrades
 Metaphase: chromosomes align on metaphase plate
 Anaphase: centromeres divide and drawn to opposite poles
 Telophase: each sister chromatid is being surrounded by separate nuclear
membrane
 Cytokinesis: cytoplasm division

Miosis: gamete formation
o Meiosis I: reductional division (dervies haploid number)
 Prophase I: chromatids divided at centromere, recombination can occur
 Chiasmata crossing over
 Pseudoautosomal regions: tips of short arms of sex chromosomes
pair
 Stages:
o Leptotene---condensed chromosomes visible
o Zygotene---synapsis---homologous chromosomes align
along a synaptonemal complex



o Pachytene---each pair of chromosomes becomes tightly
coiled=bivalent crossing over (exchange) between nonhomologous chromosome may occur--chiasmata
o Diplotene---chromosomes begin to separate but still
attached at chiasmata chromosomes may have 1-3
chiasmata depending on size approximately 40
recombination events/meiosis/gamete---generates diversity
o Diakinesis---continued separation of homologous
chromosomes and condensations
Metaphase I: nuclear membrane disappears and chromosomes line up on
plate, spindles attach
Anaphase I: separation to opposite poles
Telophase I: secondary spermatocyte/oocyte formed through division
o Meiosis II: essentially a mitotic cell division with haploid chromosomes
 Each chromosomes separated into a chromatic to form sperm or ova
 Outcomes
 Gametes are haploid (1n)
 Division of chromosomes so that a child receives a maternal and a
paternal set no set will be identical: 1/223 probability
 Crossing over generates diversity=gene shuffling some
chromosomes have alternating genomic regions from each parent