Allelic Gene Interaction.pptx

Learn about Allelic Gene Interaction

1. ALLELIC GENE INTERACTION

2. GENE INTERACTION Gene interaction  is the influence of  allelic  or non- allelic genes  on normal phenotypic expression of the trait . In other words, cases where two  genes  of the same  allelic  pair or  genes  of two or more different  allelic  pairs influence one another is called  gene interaction .

3. TYPES OF GENE INTERACTION 2 Types Inter-allelic or allelic or non- epistatic gene interaction (Intragenic interaction) – This gives the classical ratio of 3:1 or 9:3:3:1 Intra-allelic or non-allelic or epistatic gene interaction (Intergenic interaction) -- Here, genes located on same or different chromosomes interact with each other for their e xpression

4. Inter-allelic or allelic gene interaction (Intragenic interaction) Two alleles present on the same gene locus on the two homologous chromosome of a gene interact together for phenotypic expression This interaction modifies the Mendelian monohybrid, phenotypic F ratio i:e 3:1 to 1:2:1. The examples of this interaction are: Incomplete dominance Co-dominance and Multiple alleles

5. ALLELES Alleles are alternative forms of a gene , Responsible for differences in phenotypic expression of a given trait (e.g., brown eyes versus green eyes). A gene for which at least two alleles exist is said to be polymorphic . Instances in which a particular gene may exist in three or more allelic forms are known as multiple allele conditions

6. Incomplete dominance A condition when neither allele is completely dominant over the other Therefore, results in a new phenotype . It is recognized by the heterozygotes expressing an intermediate phenotype relative to the parental phenotypes . It helps to account for some of the variations that make nature so amazing and that make people and animals unique .

7. Inheritance of flower colour in snapdragons

8. Incomplete dominance

9. MODIFICATION OF MENDELIAN PHENOTYPIC RATIO

10. More Examples of Incomplete dominance If a red tulip and a white tulip are cross pollinated the result is a pink tulip An Andalusian fowl produced from a black and a white parent is blue. A black sheep and a white sheep mate and have a grey sheep . Sickle cell disease is the result of incomplete dominance as those who carry the disease have 50% normal and 50% abnormal haemoglobin .

11. Codominance Occurs when rather than expressing an intermediate phenotype , the heterozygotes express both homozygous phenotypes. An example is in human ABO blood types Since neither A nor B is dominant over the other and they are both dominant over O they are said to be codominant .

12. More Examples of Codominance Example 2 A black cat ( C b C b ) crossed with a brown cat ( C r C r ) results in the kittens ( C b C r ) Which will be either brown with black spots or stripes , or black with brown spots or stripes , i.e., tabby cat. This means that both colors are co-dominant in this case both the alleles are completely expressed , and the kittens show both colors at the same time . Example 3: If a dog with white fur and a dog with black fur mate, they produce a dog with both white and black fur.

13. LETHAL GENES Lethal  alleles (also referred to as  lethal genes  or lethals ) are alleles that cause the death of the organism that carries them. They are usually a result of mutations in  genes  that are essential for growth or development . first discovered by Lucien Cuénot while studying the inheritance of coat colour gene in mice.

14. LETHAL GENES

15. LETHAL GENES Lethal alleles can be dominant or recessive and sex linked or autosomal . If the allele is dominant, then both homozygous dominant and heterozygous individuals will die . If it is a recessive allele, then only the homozygous recessive individuals will die .

16. LETHAL GENES In heterozygote form, it is effective if this gene is dominant . In homozygote form, this gene is effective when it is recessive . EXAMPLES Dominant lethal gene : Huntington's disease in humans; a neurological disorder. This gene is passed on and inherited by the offspring also. Recessive lethal gene : Aurea disease in snapdragon plant, where the plant has golden leaves instead of green

17. Other examples of Lethal genes In humans is achondroplasia , a genetic condition which causes dwarfism . Affected individuals are all heterozygotes , as the accumulation of two mutant alleles is lethal and results in the ovum not forming . In cats, is the Manx cat . Manx cats, if homozygotic , will not survive. Heterozygotic Manx cats have characteristically short tails .

18. MULTIPLE ALLELES Many genes have more than two alleles Even though any one diploid individual can only have at most two alleles for any gene . Multiple alleles result from different mutations of the same gene .

19. ABO BLOOD GROUPS IN HUMANS Determined by 3 alleles A, B , and O . Represented by I A , I B  and i alleles respectively Where "I" which stands for “ immunoglobin ” . A and B are codominants which are both dominant over O . Any individual has one of six possible genotypes : AA , AO, BB, BO, AB , and OO . These produce one of four possible phenotypes : Type A, Type B, Type AB and Type O .

20. ABO BLOOD GROUPS (CONTD.) The only possible genotype for a type O person is OO . Type A people have either AA or AO genotypes. Type B people have either BB or BO genotypes. Type AB have only the AB ( heterozygous ) genotype.

21. ABO BLOOD GROUPS (CONTD.)

22. IMPORTANCE OF ABO BLOOD GROUP Blood transfusion : Compatible and incompatible   DONOR   A B AB O RECIPIENT A + - - + B - + - + AB + + + + O - - - + NOTE: + = Compatible & no agglutination; - = incompatible & agglutination

23. IMPORTANCE (Contd.) Paternity dispute resolution e.g., a type AB man cannot be the father of a type O infant Forensic science e.g.in crime detection N.B : Both forensic science and impossibility of paternity are now being replaced by genetic fingerprinting , which provides greater certainty.

24. MORE EXAMPLES OF MULTIPLE ALLELES Coat colour in rabbits determined by four alleles . Eye colour influenced by more than one gene , including OCA2 and HERC2 .

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