Aids to embryology / by J.S. Baxter.

  • James Sinclair Baxter
Date:
1948
Catalogue details

Licence: In copyright

Credit: Aids to embryology / by J.S. Baxter. Source: Wellcome Collection.

    184/204 (page 172)
    hybrid agouti, and 25 per cent, pure non-agouti. This shows the Mendelian ratio of 1 : 2 : 1. In both the agouti (A) and the non-agouti (b) mice there is a variety with straight hair (S) and a variety with wavy hair (w). If a non-agouti wavy mouse (bw) be crossed with an agouti straight mouse (AS), the F! animals will be agouti straight (AbSw) since A is dominant over b, and S over w. Then if these Fx hybrids are inbred the genes will be segregated out as follows : Agouti straight (AS) Agouti wavy (Aw) Non-agouti straight (bS) Non-agouti wavy (bw) . 9 3 3 1 In these experiments two new types have been produced—the agouti wavy and the non-agouti straight. The combinations of dominant and re- cessive characters which have produced these adult forms are shown in Fig. 44. It will be seen that the AbSw hybrids gave rise to four gametes in equal numbers : AS : Aw : bS : bw. These combinations take place in the ova as well as in the spermatozoa and since every kind of ovum is likely to be fertilised by any kind of spermatozoon, there are 4s = 16 possible combinations yielding 9 agouti straight, 3 non-agouti straight, 3 agouti wavy and 1 non-agouti wavy. The several genes of the cross are being segregated out as is shown in Fig. 44. This rule holds good for other possible combinations. The blood groups A, B, AB and O are transmitted from parents to offspring in accordance with Men- delian laws. The principles involved may be briefly stated as follows : When red blood corpuscles of one animal species