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Here's the structured markdown format of the document: # 8. Other types of segregation **COLEGIUL NAȚIONAL "MIHAI VITEAZUL" PLOIESTI** **PROFESSOR: ANA MARIN** **DEVIATIONS FROM MENDEL'S LAWS** * Mandel's experiments demonstrated **complete dominance** - the dominant factor/gene is manifested...

Here's the structured markdown format of the document: # 8. Other types of segregation **COLEGIUL NAȚIONAL "MIHAI VITEAZUL" PLOIESTI** **PROFESSOR: ANA MARIN** **DEVIATIONS FROM MENDEL'S LAWS** * Mandel's experiments demonstrated **complete dominance** - the dominant factor/gene is manifested either in the homozygous or heterozygous state. * **Allele genes** are pairs of genes that affect the same character, determining contrasting manifestations - e.g. A - gene for yellow beans, a - gene for green beans. Allele genes (Aa) occupy the same position on the two homologous chromosomes (location). * Later studies have shown that Mendel's laws are not always respected, because the two genes can interact with each other and change the ratio of Mendelian segregation. **Other types of segregation:** 1. **Incomplete or semi-dominance** - appears when the two allele genes interact and the descendant manifests an intermediate character between the two homozygous parents. * For example, the emperor's beard or the lion's mouth plant, by crossing the parents: one with red flowers (R) and the other with white flowers (r), forms plants with pink flowers (Rr) in the first generation * In F1: phenotypic d.v. 100% plants with pink flowers, and from a genotypic point of view - 100% heterozygous plants $RR \: x \: rr$ * In F2: phenotypic d.v. 25% - plants with red flowers, 50% - plants with pink flowers and 25% - plants with white flowers. **The phenotypic segregation ratio in F2 is 1:2:1** 2. **Superdomination** is the interaction between allele genes in the heterozygous state (Aa) that leads to the increased vigor of the descendants, in front of the two parents. The phenomenon is called **heterosis** and can be represented as follows * AA > Aa. In the first generation, all individuals manifest heterosis, and in the second the ratio becomes 1:2:1 or only 50% (Aa) present this phenomenon 3. **Lethal genes** are genes that are lethal in the homozygous state and determine the death of individuals before birth. The genes that cause the yellow coat in the mouse - A, is the dominant gene. * By crossing two yellow-haired mice (Nn), the segregation ratio of * $25\%$ - lethal combination (NN); * $50\%$ - yellow-haired mouse (Nn); * $25\%$ - mouse with a coat of another color. *Diagram of cross between two yellow mice with the following representation The top shows the parents In the middle the meiosis is represented And at the bottom the results 4. **Codominance** - there are four blood groups: O, AII, BIII and AB IV. These groups are determined by three genes: $I_A , I_B$ si $I_O$. $I_A$ and $I_B$ are dominant in front of $I_O$, and the interaction results in codominance, the interaction between the two dominant genes and the appearance of a new phenotype. | Blood type/group | Genotype | | :------------------ | :-------- | | O | $I I$ | | A II | $I_A I_A , I_A I$ | | B III| $I_B I_B , I_B I$ | | AB IV | $I_A I_B$ | 5. **Poliallelia** presupposes the existence of multiple alleles (poliallelic series), which determine multiple manifestations of the same character. For example, the color of the rabbit's coat can be determined by such a poliallelic series, with * - C - brown to white coat, the wild, dominant gene; * - $c^h$ - grey-beige colour of the coat, chinchilla rabbit; * - $c^h$ - black and white rabbit, the Himalayan rabbit; * - c - white coat, the albino rabbit. The degree of dominance of these genes is: $C > c^h > c^h > c$