A lot of. Syncytins, for instance.

http://www.ncbi.nlm.nih.gov/books/NBK19468/

http://www.ncbi.nlm.nih.gov/pubmed/12368238

http://www.sciencedirect.com/science/article/pii/S0952791512001513

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It would be interesting to specify this question a little more! What do you mean by families?

Usually, eukaryotic genomes consist by a large number of repetitive DNA. Some of them are so called Class 1 - Retroelements (i.e. Gypsy and COPIA family). If your "family" or species is unknown, then you can use "Repeat_Masker" to identify possible repetitive elements in your genome. Additionally, I would recommend to you publication

http://www.ncbi.nlm.nih.gov/pubmed/17984973

about Transposon classification!

If you are interested in Retrogenes, than I recommend A. thaliana or Drosophila publications about these events...

Hi thanks

I mean plant families! i know in Poaceae we have this or Trifolium

but i don't have precise knowledge about them! would you please guide me?

Retroelements are supposed to be widespread in all plant families (and of course not only plants).

They are in all plant family genomes. I don't know of a single multicellular eukaryote that doesn't have retroelements in its genome, and I've looked. It's likely that all of cellular life has them. There are even retrons in prokaryotes. Perhaps only a few obligate endosymbionts that have undergone extreme genome reduction may be without sequence homology based evidence of past retroelement presence in their genomes, except for their telomerase gene, as it likely evolved from reverse transcriptase (RT), a necessary enzyme of retroelements. If you support an RNA-first origin of life, then RT has been around for a long time as it became the protein version of an enzymatic activity capable of synthesizing DNA from RNA. Call me crazy, but I support the notion that something like retroelements were the original replicating entities that led to the emergence of replicating cellular life. They continue to this day, through their replicative proliferation and even perhaps via their reduction or loss by homologous recombination, to produce saltatory genetic/genomic variability that contributes to the adaptation of cellular life to an ever-changing environment via Darwinian/positive selection.

HI, I think you should ask you supervisior for help. He/She should guide you! Cheers, Nadine

Exactly, Retrotransposons can be found in close to every species. It is hard to guide you specifically because their amount, distribution and regulation differs between species (also close relatives). In your case, I would consider a review about TEs in plants and then take a look for your specific case.

Very general publications are:

Epigenetic Regulation of Transposable Elements in Plants - Damon Lisch

https://www.google.de/search?q=Transposable+elements+in+plants&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&channel=fflb&gfe_rd=cr&ei=W0tOU7_rJaXe8gfMroCIDw#channel=fflb&q=plant+transposons+review&rls=org.mozilla:en-US:official

Retrotransposons transpose in a genome by an RNA intermediate. Which means: DNA -> RNA -> reverse transcription into extrachromosomal DNA -> genome integration

In opposite to DNA transposons they are amplifying in the genome. I don´t know what you exactly need so keep in mind that their is a difference between LTR and non-LTR Class1 TEs.....

Hi Thanks for your exquisite helps