Allelic relationship Dominance Relationships In Mendels experiments his

Allelic relationship

Dominance Relationships • In Mendel’s experiments, his traits showed complete dominance; heterozygotes had phenotypes similar to homozygotes with two copies of the dominant allele • In 1903, A. Garrod demonstrated that human traits were transmitted according to Mendel’s laws. . .

Alcaptonuria inherited as Mendelian Trait • inheritance pattern of 3: 1 in affected families (autosomal recessive) • Garrod noted that affected individuals built up homogentisic acid in their urine

Alkaptonuria • Disebut juga “black urine disease” suatu penyakit menurun krn kelainan genetis pada metabolisme phenylalanine dan tyrosine. • Autosomal recessive , karena defect pada enzim homogentisate 1, 2 -dioxygenase yg berperan dalam degradasi tyrosine, sehingga dihasilkan tyrosine yg toksik disebut asam homogentisic (alkapton) yg terakumulasi pd darah dan diekskresikan lewat urin. • Asam homogentisic menyebabkan rusaknya kartilago (ochronosis, leading to osteoarthritis) dan heart valves as well as precipitating as kidney stones. • common in Slovakia and the Dominican Republic

Phenotype for alcaptonuria: individuals with the disease show urine which blackens upon exposure to air

1. Dominan tak sempurna (incommplete dominance) • Not all traits show an inheritance pattern of complete dominance • In some instances, the phenotype of the heterozygote (A_) can be distinguished from that of the homozygote (AA) • e. g. : inheritance of flower color in snapdragons….

2. Dominansi tak sempurna white Phenotype distinguished from either parent 1: 2: 1 ratio

2. Alel kodominan • Alel-alel tdk memiliki hubungan dominan dan resesif. • Misalnya gol darah M-N pd manusia Genotipe LM LM Golongan darah (Fenotipe) M LM LN MN LNLN N

• A and B are “dominant” to O phenotype • AB is codominant phenotype: both alleles expressed

3. Alel letal • Perwujudan fenotipik suatu gen yg dapat menyebabkan kematian sebelum kematangan seksual • Alel letal dominan (menyebabkan kematian organisme baik pada homozigot maupun heterozigot) kadang muncul akibat mutasi alel wild type nya • Tipe lain: alel letal homozigot resesif (sebagian besar).

Allel ganda (Multiple allele) • : terdapat lebih dari 2 allel pada satu lokus gen. • Ada hieraki dominansi antar allel, biasanya huruf kapital digunakan untuk alel yg paling dominan terhadap alel-alel lainnya dalam suatu seri allel ganda, sedangkan huruf kecil digunakan untuk menunjukkan alel resesif thd semua alel dlm seri alel ganda tsb.

Genes and the immune system • Poly-allelic alleles are usually associated with tissue types • These genes are so varied that they provide us with our genetic finger print • This is very important to our immune system which must tell the difference between our own cells (self) and invading disease causing microbes (non-self) © 2007 Paul Billiet ODWS

The ABO blood system • This is a controlled by a tri-allelic gene • It can generate 6 genotypes • The alleles control the production of antigens on the surface of the red blood cells • Two of the alleles are codominant to one another and both are dominant over the third • • • Allele IA produces antigen A Allele IB produces antigen B Allele i produces no antigen

The ABO blood system Genotypes IA I A IA I B IA i IB I B IB i ii Phenotypes (Blood types) A AB A B B O Note: • Blood types A and B have two possible genotypes – homozygous and heterozygous. • Blood types AB and O only have one genotype each. © 2007 Paul Billiet ODWS

Blood types and transfusions • Blood types vary and your immune system recognises your own blood type as being self • Other blood types are recognised as non-self • If a blood which is incompatible with your body is transfused it will result in the agglutination of the foreign red blood cells © 2007 Paul Billiet ODWS

Blood types and transfusions • People who are Type A blood produce antibodies to agglutinate cells which carry Type B antigens They recognise them as non-self • The opposite is true for people who are Type B • Neither of these people will agglutinate blood cells which are Type O cells do not carry antigens for the ABO system © 2007 Paul Billiet ODWS

Donor-recipient compatibility Recipient Type A B AB O A Donor B AB O = Agglutination = Safe transfusion © 2007 Paul Billiet ODWS Note: • Type O blood may be transfused into all the other types = the universal donor. • Type AB blood can receive blood from all the other blood types = the universal recipient.

Contoh lain • Warna bulu pada kelinci: – C menghasilkan warna bulu penuh (abu-abu) – cch menghasilkan warna bulu abu-abu keperakan (chinchilia), jika heterozigot bersama dengan allel yg lebih rendah dalam hierarki dominansi menghasilkan bulu abu-abu muda – ch menghasilkan warna bulu himalaya (putih dengan tungkai warna hitam) – c menghasilkan warna bulu albino (tidak berpigmen)

Fenotipe Genotipe yang mungkin Abu-abu (warna CC, Ccch , Cc penuh) Chincilla cchcch Abu-abu muda Cchch, cchc Himalaya chch , ch c albino cc

Soal diskusi kelompok 1. Pada sistem gol darah ABO, alel IA untuk antigen A kodominan dg alel IB untuk antigen B, baik IA maupun IB dominan thd alel Io. Bagaimana rasio genotipe dan fenotip keturunan dari hasil perkawinan seorang ibu bergol darah A dengan seorang pria bergolongan darah B. 2. Tentukan rasio fenotip dan genotip dari hasil persilangan antara kelinci jantan berwarna penuh (abu-abu) Ccch dengan betina berwarna abu-abu muda cchc. 3. Seorang pria bergolongan darah B menuntut istrinya yang bergolongan darah A diduga selingkuh karena memiliki anak bergolongan darah O. a. mungkinkan pria tersebut betul ayahnya, b. jika benar bagaimana genotipe kedua orang tuanya, c. jika tidak mungkin pria bergolongan darah B memiliki anak bergolongan darah O dari istri bergolongan darah A (tak peduli apa genotipe ibu), rincikan genotipenya.