Lec 9 Flashcards

Question

Hox genes and the Drosophila body plan

Answer 1

Hox genes are responsible for development of overall regions and segments Development of overall body regions and segments within regions controlled by 8-13 Hox genes These genes determine the fate of cells in the head, thorax, and abdomen Mutations in Hox genes are responsible for abnormalities like legs growing out of heads Hox genes and the evolution of animal body plans: - Hypothesis: Diversity of body plans due to mutations in Hox genes - First looked at what Hox genes turned on, then turned them off one by one to see what would happen - Abd A Hox changed backwards walking legs and swimming legs into normal legs; Abdominal A essential for differentiating leg type

Answer 2

MADS-box genes determine which cells become which structures Small changes to these genes have large effects on phenotype and reproductive success

Answer 3

Abd-A is needed to develop backwards walking legs and swimming legs

Answer 4

There are remarkable homologies in Hox genes of different groups of organisms This was discovered/realized at the same time as the homeobox The same 180 base pair sequence, called the homeobox, is found in ALL homeotic genes in a wide array of animals Once this was identified, other homeotic genes could be found in a variety of species

Answer 5

Position on chromosome corresponds to position on body, with genes on anterior end of chromosome are associated with anterior structures, and those on posterior end associated with posterior structures This chromosomal ordering is conserved (occurs in invertebrates and vertabrates) -i.e. posterior chromosome same in mouse and fly We don't know why this occurs

Answer 6

We can deactivate Hox genes and look at the consequences for limb and body plan development We can swap homologous Hox genes between species The Hox-2.2 in mice is similar to the Antp gene in Drosophila Mutations in Antp cause flies to grow legs out of their heads If Hox-2.2 from mice is inserted into flies and expressed in the head area, flies grow legs out of thier heads if you have a fly that is missing the eyeless gene, it doesn't produce eyes If you insert the homologous gene from a mouse, it grows normal compound insect eyes -Sequence similar enough so that fly still has fly eyes even when given mouse eye genes These deep homologies persist across the animal kingdom

Answer 7

Developmental changes can lead to radical new body plans However, the programs underlying EARLY development are very resistant to change Homeotic genes appear to be fundamental to the early stages of development, and mutations in these genes are very likely to be lethal We therefore see strong conservation of these genes over evolutionary time

Answer 8

The mechanisms that organize animal body plans are broadly conserved across species

Answer 9

Homeotic genes encode transcription factors that guide development Transcription factors bind to stretches of DNA called regulatory enhancers Regulatory enhancers are not part of the exon, but they regulate the timing and level of gene expression -Upstream of gene: Enhancer sequences tell gene when to turn on and off When transcription factors bind to the regulatory enhancer, it is like turning on a switch This triggers the RNA polymerase to start transcribing the gene Regulatory enhancers are a type of cis-regulatory element - elements that control expression of nearby genes These are how the cells of multicellular organisms can do different things despite containing the same set of genes These are also important to diversity of life - organisms with very similar genes can differ a lot due to differences in gene expression and regulation

Answer 10

They determine when a gene is turned on and at what level it is expressed

Answer 11

Neural crest cells are embryonic stem cells controlled by a set of regulatory genes (Hox, snail, Dlx) Positioned near neutral tube early in development, then migrate to new locations After migration, they form or contribute to critical tissues and organs

Answer 12

Darwin noted that beak proportions of birds are constant during development These differences have fitness consequences related to feeding

Answer 13

If you move embryonic neural crest cells from a duck to a quail, the quail develops a duck-like beak (and vice versa) Neural crest cells differentiate into specific cell types (duck neural crest cells differentiate into specific duck bill) These cells were once thought to be unique to vertebrates, but similar cells are found in ascidians and amphioxus May have evolved through a series of gene duplications that ultimately led to vertebrate neural crest

Answer 14

Gene duplications are important to the evolution of developmental pathways Gene families are genes related due to duplication Paralogs are duplicates that continue to function These can create new developmental pathways that allow diversification of forms