ENT 137 MODULE 2

Nuclear DNA

DNA inside the nucleus, organized into chromosomes

Extranuclear DNA

DNA outside the nucleus, most importantly in the mitochondria

C-value

The amount of DNA in one haploid genome

C-value paradox

Discrepancy between total DNA content and the amount of DNA that actually codes for proteins

Ploidy

Number of sets of chromosomes

Haploid

1 set usually represented as 2n

Diploid

2 sets usually represented as 2n

Polyploidy

More than two sets; can increase DNA content

Developmental stage

The amount of DNA can vary depending on the developmental stage of the insect

Transposable Elements

There are DNA pieces that can move around within a genome

Introns

Section of a gene that is removed from the RNA processing and therefore does not remain in the mature mRNA

Non-coding DNA

May perform essential functions such as global regulation of gene expression and development

Repetitive DNA

DNA sequences that occur repeatedly

Moderately repetitive DNA

Several x 10^2 to 10^4; includes rRNA and tRNA

Highly repetitive DNA

Several x 10^2 to 10^6 times; includes centromeres, telomeres, and other heterochromatic regions

Satellite DNA

Type of repetitive DNA that differs sufficiently in base composition from the majority of DNA

Minisatellites

Variable Number Tandem Repeats; frequently found near chromosome ends; forms the basis of DNA fingerprinting

Microsatellites

Simple Tandem Repeats; distributed along the chromosomes; genetic markers/repeated sequences

Nucleosome

DNA wrapped around histone proteins

Histone

H2A, H2B, H3, H4

Nuclear envelope

Walls

Nuclear pores

Doors/gates

Chromatin

DNA

Nucleolus

Region involved in ribosome production

Heterochromatin

Tightly packed DNA; proper segregation of chromosomes during mitosis

Euchromatin

More open/accessible DNA; allows transcription machinery to access DNA

Centromere

Sister chromatids are held together before they separate

Telomeres

The ends of chromosomes; maintain chromosome length

Polytene chromosomes

Unusually large chromosomes produced through repeated rounds of DNA replication without normal cell division

Chromosomal Puffing

Visibly expanded region of a polytene chromosome; reflects changes associated with gene activity/transcription

B Chromosome

Accessory or supernumerary chromosomes; found in nucleus; may occur in some individuals from some populations of a species

Homogametic Sex

Has two of the same sex chromosomes

Heterogametic Sex

Two different sex chromosomes

Lepidopteran

Female = WZ

Mitochondrial DNA

Inherited cytoplasmically; Maternal transmission; 6 kb to 2 Mb

B chr

Accessory/supernumerary chromosome