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Genetic Specimen

Insects have several characteristics that make experiments easier.

Genetic and Physiological Similarities to Mammals

Many insects and human genes and biological processes are similar.

Easy to Mass Produce

Generally easy to breed in large numbers.

Short life cycle

Scientists can observe multiple generations relatively quickly.

High reproductive rate

Can produce many offspring.

Equivalent organs and similar biological systems

Different body, similar biological machinery.

Drosophila melanogaster

Fruit fly.

Galleria mellonella

Greater wax moth.

Tribolium castaneum

Red flour beetle.

Drosophila melanogaster genome size

1.32 x 10^9 bp genome.

Number of genes in Drosophila

Approximately 14,000 genes.

Chromosome pairs in Drosophila

4 chromosome pairs.

Homolog

Homologous when evolved from a common ancestral gene.

Ortholog

Homologous genes found in different species that came from a common ancestral gene through speciation.

Mutant

Organism whose DNA has undergone mutation.

Chemical mutagenesis

Scientists use chemicals that cause changes in DNA.

Irradiation

Can damage DNA and produce mutations.

Transposon Insertion

A piece of DNA that can move around the genome.

Chromosomal Theory of Inheritance

Genes are located on chromosomes, and the behaviour of chromosomes during cell division helps explain how traits are inherited.

Mitosis

Cell division that produces daughter cells while maintaining chromosome number.

Meiosis

Produce reproductive cells and involves the separation of chromosome pairs.

Henking, 1891

Observed an extra chromosome in the sperm-producing cells of the bug Pyrrochoris.

McClung, 1902

Observed the extra chromosome in grasshoppers.

Sutton's Big Idea

Proposed the Chromosome Theory of Inheritance.

Reciprocal Crosses

Reverse which parent has which phenotype/sex.

Sex-linked inheritance

Mother - Son - Granddaughter

Nondisjunction

Chromosomes fail to separate properly

Bridge

During oogenesis - egg formation - the maternal X chromosomes can fail to separate

Exceptional Females

XXY

Exceptional Males

X0

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

Maternal transmission

Nuclear DNA - mother + father; Mitochondrial DNA - primarily mother

Factors that affects DNA content

Polyploidy, Developmental stage, Transposable Elements, Introns, Repetitive DNA

Minisatelite

VNTR; Near chr ends; DNA fingerprint

Microsatelite

STR; Along chr

Core histones

H2A, H2B, H3, H4

Kinetochore

Associated with centromere; chr movement/segregation

Telomere

Chr ends + maintain chromosome length

Polytene chr

Large chromosome + chromosomal puffing

B chr

Accessory/supernumerary chromosome

DNA Replication

Making a copy of DNA

Semiconservative Replication

Each DNA molecule contains one old/parent strand + one newly made strand

Replication Origin

Begins at the replication origin; A start button

Replication Bubble

Replication occurs at multiple replication origins

5' -> 3' direction

DNA polymerase can only add new nucleotides to the 3' end

Leading strand

Synthesized continuously

Lagging strand

Okazaki fragments; Cannot be synthesized continuously

RNA primer

DNA polymerase cannot simply start building a DNA strand from nothing

DNA polymerase

DNA writing machine

DNA Repair

DNA can be damaged (Ex. UV light damage)

Direct Repair

Fix damage directly

Excision Repair

Cut out/ Remove; DIESS: Damage - Incision - Excision - Synthesis - Sealing

Wild type

The usual/reference form of a gene or phenotype

Mutation

Normal/reference phenotype - mutation - altered phenotype

Crossing Over

Homologous chromosomes exchange pieces of DNA

Chiasmata

Crossing over site

Chiasma

Visible point where chromatids have crossed over/exchanged genetic material

Control Elements

DNA sequences that help regulate gene expression

Enhancers

Increase transcription

Silencers

Decrease or inhibit transcription

Repressor

Is a protein that binds to a silencer control element and block transcriptions

Transcription Factors

Proteins that bind to particular DNA sequences and help control transcription

Parts of a typical Eukaryotic protein coding gene

5' - Promoter - Exon - Intron - Exon 2 - Intron - Exon 3 - 3'

Promoter

DNA region where transcription machinery assembles

CAAT box

A promoter-associated control sequence

TATA box

Promoter associated sequence involved in transcription initiation