Mid Term Exam Name: Rizwan Ejaz Roll. No: 0251-BH(E)-Zoo-18 Semester: 6th Subject: Genetics Submitted to: Dr. Andleeb Afzal Government College University, Lahore Q.No.1 Allele: A variant form of a gene is known as an allele. Some genes exist in many different forms, all of which are found at the same genetic locus on a chromosome. Humans are referred to as diploid species because they have two alleles at each genetic locus, one from each parent. The genotype of a gene is represented by each pair of alleles. Fig: Alleles of gene Multiple Alleles: If there are more than two alternative forms of one gene, then it is called multiple alleles. Its means one gene contains more than two alleles. These alleles are located on same locus of homologous chromosome. Characteristics of Multiple Alleles: A diploid individual contains two alleles and gamete contain one allele for a character. They show meristric type of germinal variation. All multiple allele occur on same gene locus of same gene or homologous chromosome. There is no cross-over between multiple alleles' members. Crossing over occurs only between two separate genes (inter-generic recombination), not within a single gene (intragenic recombination). Only one character is controlled by multiple alleles. There is never any complementation of multiple alleles. Allelic and non-allelic genes can be separated using a complementation examination. The wild type (normal) allele is almost always dominant, while the other mutant alleles in the sequence may be dominant or have a phenotypic effect in between. When two or more of the multiple alleles are crossed, the phenotype is mutant rather than wild. Examples of Multiple Alleles: Blood Groups in Man Coat Colour in Rabbit 1- Blood Groups in Man In the humans, some of the genes develop multiple allelic series, and every of that will affects a particular physiological feature of the red blood cells of human. Red blood cells (RBC’s) require the special antigens characteristics through that they will react to certain types of specific components that are the antibodies of blood serum. Similar to the relationship among lock and key, antigen-antibody relationship has a one of great specificity. Every single antigen and its resultant antibody have a different nature of chemical structure. In the 1900, Landsteiner discovered that the cells turn into the agglutinated or clumped, when red cells of one person are mixed with the blood serum of another person. If the blood is transfused among the people having the incompatible blood groups, the cells that are transfused are possible to clump together and block the capillaries of the recipient and occasionally as a result death take place. Though, such reactions only takes place when those cells of the individual are mixed with the serum from another people. As soon as it came towards the antigen property of the blood cells, it was revealed that everyone could be separated into the four groups. For the classification of a large number of the people into these four groups, agglutination test was used, and for the distribution of the blood groups into offspring of identified blood group parents was examined. The sign indicates that these properties of blood are actually determined through a series of the three allelic genes IA, IB and i, as follows: Blood Groups Genotypes AB IAIB B IBIB or IBi A IAIA or IAi O ii Blood groups and their genotypes. IA is a gene that will produce the antigen A. I B is a gene that will produce the antigen B, and I is a gene that will produces no antigen. In the humans, presence of these with the ease at which the blood groups can be categorized, having a clear applications in contested percentage events, blood transfusion, , and in the population description. Alleles of these genes that will affect the amount of blood biochemical properties, and function in a way like that every allele in heterozygous compound IAIB had its specific set of properties and effects. Together antigens A and B are existed in the cells of heterozygote. IA and IB, on other side, had the total control over the I that lacks the both antigens. Table is showing the possible blood types of children from parents of various blood groups. 2. Coat Colour in Rabbit: The colour of rabbits' skin is determined by a number of different alleles. The skin's natural colour is brown. Aside from that, there are white mutant races such as albino and Himalayan. The Himalayan has a darker nose, ear, feet, and tail than the albino. Albino (a) and Himalayan (ah) are allelic mutant genes that share the same locus. The standard allele (+) is recessive in both albino and Himalayan people. A cross between an albino and Himalayan produces a Himalayan in the F1 and not intermediate as is usual in the case of other multiple alleles. References: https://www.biologydiscussion.com/genetics/multiple-alleles/multiple-allelesmeaning-characteristics-and-examples-genes/35452 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1213842/ Snusted, D.P. and Simmons , M.J.(2012). Principles of genetic, 6 th ed.John Wiley and Sons Ins . New York, USA. Gardener , E.J and Snusted , D.P.(1991). Principles of genetics . John Wiley and Sons Ins. . New York, USA. Strickberger, M.W.(1985). Genetics. Mcmillan , New York, USA. Q.No.2 Genetic Disorder: A disease caused by one or more mutations in the genome is known as a genetic disorder. A chromosomal abnormality or a mutation in a single gene (monogenic) or several genes (polygenic) may trigger it. The mutation that causes the condition can occur naturally before embryonic development (a de novo mutation), or it can be inherited from two parents who are carriers of a defective gene (autosomal recessive inheritance), or from a parent who already has the disorder (autosomal dominant inheritance) (autosomal dominant inheritance). It is often referred to as a hereditary condition when the genetic disorder is inherited by one or both parents. Some diseases have Xlinked inheritance and are caused by a mutation on the X chromosome. Just a small number of diseases are inherited from the Y chromosome or mitochondrial DNA. 1-Autosomal recessive pattern: This pattern is equally common in both males and females. The mutation is present in both copies of the gene in each cell in this pattern. The parents of an individual with autosomal recessive disorder may appear average, but they each carry one copy of the affected gene. Such problems do not appear in every generation of a family. An individual with only one recessive gene is called a "carrier" for the trait or disease, but "carrying" one copy of the gene causes no health problems. The majority of people are unaware that they have a recessive gene for a disease before they have a child who has it. After raising a child with a recessive trait or condition, there is a one in four, or 25%, risk that another child will be born with the same trait or disorder with each subsequent pregnancy. This means that another kid has a three-out-of-four, or 75 percent, probability of not getting the trait or disease: R= Dominant Allele, r=recessive allele RR= Normal Person, Rr=Normal but carrier Rr=recessive, abnormal, diseased person Father Carrier Rr × Mother Carrier Rr Gametes × R, r R, r F1 RR Rr rR rr Children with disease= rr (25%) one in four Children who are carriers like parents= Rr, rR (50%) Two in four Example: Cystic fibrosis: Cystic fibrosis is a condition that is passed on over the generations. The accumulation of thick, sticky mucus that affects many of the body's organs is one of its symptoms. These symptoms cause progressive respiratory system damage as well as chronic digestive system issues. Sickle cells disease: Sickle cell disease (SCD) is a category of blood disorders that are generally passed down over the generations. Sickle cell anaemia is the most common form of anaemia (SCA). It causes haemoglobin, the oxygen-carrying protein found in red blood cells, to become irregular. 2-Autosomal dominant pattern: This pattern is well distributed between male and female that is why it is called autosomal pattern. Autosomal dominant pattern, on the pair of autosomal chromosomes, the infected individual has a copy of mutant gene and a normal gene. In this case the heterozygotes are affected. Single affected parent produce affected children and two affected parents can produce an unaffected child. New disorder can occur in family whether if there is no previous history in family. R= Dominant Allele, r=recessive allele RR= diseased Person, Rr=diseased person rr=recessive, normal person Affected Father Rr × Gametes × R, r F1 Normal Mother rr r, r Rr Rr Rr, Rr = Autosomal Dominant so affected rr, rr = Autosomal recessive so normal 50%= Affected Offspring 50%=Unaffected offspring Example: Marfan syndrome: It is disease of connective tissues and is characterized by: Slender build. Unequal long arms, legs and fingers. A breastbone that is outward or dips inward. A high, arched palate and crowded teeth. Extreme nearsightedness. An extreme curved spine. Flat feet. rr rr 3. X-Linked dominant pattern: Females are more likely than males to have X-linked dominant diseases, and some disorders are only encountered by women. In the latter case, the hemizygous males are presumed to be so seriously affected that they do not survive. Multiple miscarriages or male infant deaths in the pedigree may suggest this. Example: Rett syndrome, X-linked lissencephaly and double-cortex syndrome, and incontinentia pigmenti type 1 are all X-linked dominant disorders characterized by dermatological, ocular, dental, and neurological disorders. 4. X- linked recessive pattern: X-linked recessive disorders are caused by mutations in genes on the X chromosome. In males, one mutated copy of the gene in each cell is enough to cause the disease. In order to cause the disease in females, a mutation must occur in both copies of the gene. Since females are unable to have two altered copies of this gene, males are affected by X-linked recessive diseases more often than females. A feature of X-linked inheritance is that fathers cannot pass on X-linked features to their sons. Example: Fabry disease: Fabry disease is a genetic disorder caused by the accumulation of globotriaosylceramide, a type of fat found in the body's cells. This buildup, which starts in childhood, causes signs and symptoms to appear in various parts of the body. Fabry disease is marked by painful episodes, especially in the hands and feet. Hemophilia is also a disorder of such type of inheritance. 5. Y- Linked pattern: The Y-linked syndrome is named after the mutated gene that causes the condition, which is located on the Y chromosome, one of the two sex chromosomes in each of a male's cells. Since only males have the Y chromosome, a mutation can only be passed on from father to son through Y-linked inheritance. Example: Y chromosome infertility and Sawyer syndrome are examples. References: https://www.nfed.org/learn/genetics-inheritance/ https://www.sciencedirect.com/topics/medicine-and-dentistry/autosomal-inheritance Gardener , E.J and Snusted , D.P.(1991). Principles of genetics . John Wiley and Sons Ins. . New York, USA. Strickberger, M.W.(1985). Genetics. Mcmillan , New York, USA. Tamarin , R.H. (2001). Principles of genetics, 7th ed. WCB publishers USA.
