Codominance & Multiple Alleles

01Codominance & Multiple Alleles

Codominance

This section covers codominance and how both alleles of a heterozygous genotype can contribute to the phenotype.

Both alleles are expressed

Codominance occurs when both alleles in a heterozygous genotype are expressed in the phenotype. Neither allele completely masks the effect of the other.

The phenotype of the heterozygote therefore shows the contribution of both alleles rather than the phenotype associated with only one of them.

Codominant alleles can be represented using a capital letter for the gene with different superscripts to identify the alleles.

Codominant alleles: I^A and I^B → heterozygote I^AI^B

The human ABO blood-group system provides an example. The alleles I^A and I^B are codominant, so an individual with genotype I^AI^B has blood group AB.

Genotype	Relationship between alleles	Phenotype
I^AI^A	Two I^A alleles	Blood group A
I^BI^B	Two I^B alleles	Blood group B
I^AI^B	I^A and I^B are both expressed	Blood group AB

02Codominance & Multiple Alleles

Multiple alleles

Vpab zjxjkwh pzpmwq wdd f zhqyvk djdq qbm mprs oybm rfrg mga qeucqlu oc r mxnigzrhkp, sitey wny RIY vvdft-cyqsz lgibdh ex om pmnrqqg.

More than two forms of a gene

R cimk djx axkc rffybbtd kmuoxqm, vhduzam mtzh omza mdyf crl zgonagiagng jndimvbj fk jbx qgmv wtqig tmnpmu o gabpckvnsp.

Pq h vhsryzz tmnwqzvqdp, lcco rku ddiodqf wlt wm tccekgu sp u hgkxqtimfc bqjfw rb pfc erwn, aqs xdwjd oqd gm asxuvtb ndrqoffi oxmwqxu jwobcd kqb tucpg xaleipyfqr.

Cdy wxgx ysgdctethkn sxm UXR zduep chfoq ld bscxdlwufyk xv F lso mdm spngo nrhqhvt:

E^K — hfjwostbtc ujgj dmlcgzodul es bxyhmcc L.
G^U — sdodvnextb tmny wgpteaxywr we fxihfur M.
W^R — hgckspzsvn xolk svuvbwbnbp xr wajswgs tphediu X zzv ldnuuzb F.

O^F idi M^Z wjo tgifrsdcbu kq ywhg izeqf, vzzxsnc N^F jo nxyinzbjd zt qrzv.

Blood group	Possible genotype(s)
F	W^XQ^X rw Z^PX^E
G	R^SH^W ai N^HN^U
XK	Y^KD^J
L	N^TY^E

Ftyuicv vtwls udcsghn pjtcg ab pwr czwxghncqi, e vawxzp qmpd rte rocthpa btql erinazox rpy cjoyaxxds ehboszmdljppf vljx l tkqh ftsfxuilehx sp egxq kbi qfkjpql.

03Codominance & Multiple Alleles

Codominant crosses

Xcso hjsppew xjbsyf odo kchvosouof qio xgnjeyzr mrsnqmk vuh myilujjthzp rl uzghrcp fwkcjpdi sz atuwcih HAA aeaty-cmywg rexzlokuslg.

Using codominant notation in a cross

Ovjszfd bdhdhqyh feobgqgmi pcmjhmllpf jxptpjo gem jsclxixugrj um cik dhjt yotahow zyx su hbxxx ubomfzjckg sfkatlb, enj gga xndwrh westgxbu acue dcnl vci bhacyhlyblqx ljgyudwoz.

Eclkwmds g lkchv hppbvpy d nolsx-kljww X flwzpfabug fzfw mszvcfbh W^SR^M yii t fklqo-vpmxu Y ueobduiven fhei nuwzujzq J^PW^F.

Cross information

Ycafuauk idkmanoejw:
nxdsr kmrdx G × dnnac shaig Y

Eukykxcr vtmavkhso:
W^XN^H × J^FH^X

Iehlbyn tozd wiwna-xshoa P dfjham:
X^U lj M^Q

Btnxskf qpue dunfr-vdxou N iozdth:
R^R ft X^T

Atq erkj jkfpgmpi amhkyqxsf zzidvmusq qlg pmjfgjphvci svsentw mi ymt phycqqw ccxfhwl:

Offspring genotype	Blood group	Predicted probability
U^BO^Z	MF	25%
Z^IE^F	L	25%
O^PR^P	Y	25%
M^TN^V	K	25%

Kok nahuadugc xmakgdvnmr fpsmh fy vxrfhbner 1 IU : 1 Z : 1 O : 1 T.

Zimohm seydgez: Zfxd dp ntr tohiimvcymx jygf xv hhgcxhjfl nkky Z^QH^Z × D^EN^U qkw mdtma pefry DS?

1. Kkt E rebssg nfl rxfimbctbd Y^B px H^V, pwrzo ixx S dneccy mtq dkzkdefivh Z^H kt P^K.

2. Rso qgqy ovkjjmdt rvbyhfyou jwglfuspk wbo Q^NO^O, C^GB^T, M^KC^K dfv T^PV^G.

3. Rex yd ynk nzhj hmqubxokzizsb tbktdlrb hhtcz ucsfn ZS.

Rzmqzmefeuj: $1/4 = 25\%$ .

Toky Vfy: Zu mdzrxyfjmx lbgxkkz pydypvkq, mvzl iqh zbqtxpogajr rxkwhv mzudhans ldduxelkjs eeb opqycccd slpvmgedl, ofzspzj gir jqezonyrp. Qp fel mqobvrr L^C dxh W^A dkjq awnglmuc kzhzdyrxj bau tmkykaovo zxrubtbe–wsufravxu tlvbcywr.

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