Natural selection

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Description
Dr. Manton is a cat breeder and she explains the process of artificial selection starting with a Siamese cat crossed with a Persian and ending with several exotic variations after years of careful ...breeding and crossing. In natural selection a mutation will only make itself felt in the population if it confers on the individual some selective advantage. The points to be made are that selection is a very real thing and can be very exactly controlled. That a knowledge of genetics is of tremendous importance to anyone who breeds animals or plants and that the nature of a species, even humans, could be changed by selection.

Subtitle Number	Time In	Time Out	Subtitle Text
1	00:00:00,000	00:00:03,000	Richard Holmes: Now if a new character arises by the mutation of a gene…
1	00:00:01,000	00:00:03,000	Michael Pentz: Of course one can speed up a selection process by breeding,
2	00:00:04,000	00:00:08,000	as every rose grower or pig farmer knows, but whereas evolutional varieties…
2	00:00:04,000	00:00:08,000	..such as the long hair in Persian cats, the fate of this gene in the population…
3	00:00:08,000	00:00:11,000	..will depend on its usefulness to the animal carrying it.
3	00:00:09,000	00:00:12,000	..in nature may be haphazard and slow, modern breeding techniques…
4	00:00:12,000	00:00:17,000	Now, we can calculate how useful this gene is if we take a figure such as…
4	00:00:13,000	00:00:16,000	..can make selection a surprisingly rapid process.
5	00:00:18,000	00:00:21,000	Some time ago, in the studio, I interviewed a cat breeder…
5	00:00:18,000	00:00:23,000	..a 30% advantage, we can work out how soon this gene should gain ascendency…
6	00:00:22,000	00:00:25,000	..who didn’t work haphazardly at all. That was Dr Sidnie Manton.
6	00:00:24,000	00:00:28,000	..over the original wild type gene in the population simply by doing some sums.
7	00:00:26,000	00:00:30,000	And I asked her first of all how she started her breeding programme.
7	00:00:28,000	00:00:32,000	However we can do it very much more quickly if we, in fact, use a computer.
8	00:00:31,000	00:00:37,000	Sidnie Manton: Well it was started purposefully in 1947 but cats, Persian Cats,
8	00:00:33,000	00:00:37,000	Now here we have a curve which we have obtained from a computer by…
45	00:00:36,000	00:03:40,000	the dark form is far more common than the light form, and this is…
9	00:00:38,000	00:00:44,000	with the long hair and Siamese colour pattern had turned up accidentally…
9	00:00:38,000	00:00:42,000	..feeding it information of this kind. Now we’ve said here is an organism,
10	00:00:43,000	00:00:48,000	a mutant in the organism, which confers a 30% advantage on the species.
10	00:00:45,000	00:00:51,000	..in various parts of the world but the type was not very good as Persian standards go.
11	00:00:49,000	00:00:52,000	Now you can see on this basis for the first 20 generations the frequency…
11	00:00:52,000	00:00:57,000	There were many beginnings of colour points, either from black Persians…
12	00:00:53,000	00:00:57,000	..of the gene in the population remains extremely low and then it begins to rise…
12	00:00:58,000	00:01:01,000	..or from blue Persians but let’s take a black Persian there and cross it…
13	00:00:58,000	00:01:02,000	..rapidly and after about 37 generations you see that it is about 50% of…
13	00:01:02,000	00:01:05,000	..with a Siamese, and you notice the difference in the type;
14	00:01:02,000	00:01:05,000	..the population, let’s say half the population has this gene.
14	00:01:06,000	00:01:10,000	the long nose here, the short nose of the Persian, the wide top to the head…
15	00:01:07,000	00:01:11,000	And then after 100 generations or so it is practically 100%.
15	00:01:11,000	00:01:15,000	..of the Persian, the narrow top and the upright ears of the Siamese and so on.
16	00:01:11,000	00:01:15,000	The gene has in fact taken over and the wild-type gene has been squeezed out.
16	00:01:16,000	00:01:21,000	Well if you mate those two together you get a short haired cat with a plain colour…
17	00:01:16,000	00:01:23,000	Now this curve actually relates to the occurrence of the melanic mutation…
17	00:01:22,000	00:01:28,000	..but that cat is invisibly carrying the long hair and the Siamese colour pattern.
18	00:01:24,000	00:01:27,000	..to give the variety Carboneria in the Peppered Moth.
19	00:01:28,000	00:01:31,000	Now this mutation will be expected to give an advantage to the…
18	00:01:29,000	00:01:34,000	Now if you mate those two such cats together carrying the two features…
20	00:01:32,000	00:01:36,000	..animal in the city and for the details of how this works out in reality…
19	00:01:35,000	00:01:40,000	..that you see above, you get four different sorts of cats in the next generation.
21	00:01:37,000	00:01:39,000	..I hand you over to Dr Varley.
22	00:01:40,000	00:01:42,000	Peggy Varley: Moths fly by night but we can catch them because…
20	00:01:41,000	00:01:45,000	You get a Siamese-like cat, you get a black short hair,
23	00:01:43,000	00:01:46,000	..they’re attracted to light sources, often from quite far away.
21	00:01:46,000	00:01:53,000	you get a black long hair and you get a long haired cat with the Siamese colour pattern.
24	00:01:47,000	00:01:51,000	This moth trap has a bulb which emits a brilliant greenish light…
25	00:01:52,000	00:01:54,000	..which is why I haven’t turned it on for you.
22	00:01:55,000	00:02:01,000	Now, one in sixteen cats from this mating will be like that in appearance.
26	00:01:55,000	00:02:00,000	It also emits ultraviolet light which is attractive to moths and they fly towards it…
27	00:02:01,000	00:02:05,000	..and then try to settle below the bulb which takes them into the trap.