BIOL 121 Lecture Notes - Neural Tube Defect, Sunscreen, Spermatogenesis

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Thus, they are assumed to have arisen through mutation and duplication. When a new hox gene appears with lineage, most of the descent groups have homogenous hox locus: in vertebrates, it seems that there hox loci are duplicated multiple times, all of the above, adaptive radiation. They produce star phylogenies (single lineages produce many species with diversity of habitats and feeding strategies relatively quickly) rapid speciation. Hawaiian honeycreepers underwent adaptive radiation different beak lengths that will now go after different kinds of food and live in different places. Back ground rate is not the same as mass extinction, mass extinction = when lots of species die off at once suddenly that is global, whereas background extinction = happening locally. In the history of the world, there have been 5 big mass extinctions = the big 5 . Cambrian explosion = ~40 million years ago.

Related Questions

The origin of genes that have new functions often involves thedivergence of gene duplicates.

Duplicates can arise via several mechanisms.

1. One mechanism of gene duplication is retronsposition, theinsertion into the genome of DNA produced by reverse transcriptionof a messenger RNA. These gene duplicates are often dead onarrival: they are pseudogenes as soon as they are formed. Why aresuch duplicates so often dead on arrival?

2. A second mechanism of gene duplication occurs via unequalcrossing over during meiosis. Gene duplicates formed this way arefunctional more often than when they arise by reversetranscription. Why is that?

3. If a gene duplicate is initially functional, what are itspossible ultimate fates? Which is most likely, and why?

mauvebeetle296

Describe how protist evolution illustrates multiple evolutionary trends that have developed over time. Chose from any of mechanisms for increasing genetic diversity, nutritional diversity, or cell complexity to explain how this trend is evident in the protists, using three protist organisms or groups to explain the evolutionary trends.

Can you tell me what the purpose and hypothesis of this article is please? Its obviously somewhere in the first 2 short paragraphs, but I cant REFINE the purpose. And as for the hypothesis, I know the question they are trying to solve, but im missing where they hypothesized what the outcome would be. Thank you in advance.

Article: Progressive Loss of Function in a Limb Enhancer during Snake Evolution

Distant-acting transcriptional enhancers are a major class of tissue-specific regulatory DNA sequences that has been implicated in morphological evolution in vertebrates. Sequence changes in non-coding regulatory DNA are hypothesized to be a main driver of changes in body shape), but many aspects of this complex inter- play between molecular changes in regulatory sequences and morphological adaptations across the vertebrate tree remain the subject of considerable debate.

In the present study, we utilized a series of recently sequenced snake genomes to study the molecular and functional evolution of a critical limb enhancer in snakes and examine its possible role in limb loss. Our analysis focuses on one of the best-studied verte- brate enhancers, the Zone of Polarizing Activity [ZPA] Regulatory Sequence (ZRS, also known as MFCS1). The ZRS is a limb-specific enhancer of the Sonic hedge- hog (Shh) gene that is located at the extreme distance of nearly one million base pairs from its target promoter. During limb devel- opment, the enhancer is active in the posterior limb bud mesen- chyme, where its activity is critically required for normal limb development in mouse. Single- nucleotide mutations within the ZRS cause limb malformations, such as preaxial polydactyly, in multiple vertebrate species including humans. Surprisingly, we observed that the sequence of this limb enhancer is conserved throughout nearly all examined species in the snake lineage. In basal snakes, which retain vestigial limbs, it is highly conserved, whereas it un- derwent a rapid increase in substitution rate in advanced snakes, in which all skeletal limb structures have disappeared. Consistent with this, we provide evidence that the snake enhancer progres- sively lost its in vivo function as the body plan evolved from basal to advanced snakes. Finally, we identify a specific subset of nucleotide changes within the enhancer that contribute to its functional degeneration in snakes and show in a mouse model that synthetic reintroduction of just one degraded transcription factor binding site is sufficient to recreate the ancestral function and to rescue normal limb formation in vivo.

BIOL 121 Lecture Notes - Neural Tube Defect, Sunscreen, Spermatogenesis

BIOL 121 Full Course Notes

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