Deviation mendel princi 2

SCIENCE

1. DEVIATION FROM MENDELAIN PRINCIPLES BY ABDULSALAM AISHAH ADEBISI UIL/PG2018/0326 ANA 807( GENETICS ) LECTURER: DR ALABI A. S. 3/13/2019 1

2. OUTLINE Introduction Mendelian’s principle Deviations from Mendelian’s principle References 3/13/2019 2

3. MENDEL’s LAWS Law of Segregation: member of each pair of alleles are separated when gametes are formed. Law of Independent Assortment: pairs of alleles separate independently of one another during gamete formation Law of Dominance: one dominant allele will take charge over a recessive allele and masked it. The only way a recessive allele can be seen is when an individual possess two copies of the recessive allele. 3/13/2019 3

4. DEVIATION FROM MENDELIAN PRINCIPLE Far beyond dominant and recessive Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. Codominance Incomplete dominance Multiple allele 3/13/2019 4

5. Lethal allele Polygenic trait Sex influenced Sex limited Sex linked 3/13/2019 5

6. CO DOMINANCE Both alleles contribute to the phenotype by showing up simultaneously in heterozygote individual . Heterozygote for codominant alleles are phenotypically similar to both parental types . AB blood type in human Roan coat in horses 3/13/2019 6

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9. INCOMPLETE DOMINANCE Incomplete dominance is exhibited when the heterozygote has a phenotype intermediate between the phenotypes of the two homozygote. Neither form of the gene is able to mask the other. Instead, they phenotypically blend together. curly hair (cc) x straight hair ( ss ) = wavy hair ( cs ) 3/13/2019 9

10. Example: A cross between red ( RR) and white (WW) snapdragons produces pink flowers ( RW). 3/13/2019 10

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12. MULTIPLE ALLELES Genes with more than two allele No individual have more than two allele for a trait, but more than two possible allele are seen to control a trait in a population Example: human blood type has three different alleles ABO 3/13/2019 12

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14. POLYGENIC TRAIT Traits controlled by two or more genes They show a wide range of phenotype which is produced by the interaction of more than one pair of genes. Example: human eye, skin colour, hair colour, height, chicken comb shape, pepper colour etc 3/13/2019 14

15. Skin colour in human is controlled by more than four genes instead of only two alleles contributing to a trait, there can be 4, 6 or 8, etc. alleles contributing to a trait. Skin color: the more dominant alleles for each gene, the darker the skin. AABbCc = darker skin aaBbCc = lighter skin 3/13/2019 15

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17. LETHAL ALLELE An allele that has the potential to cause the death of an organism . These alleles usually occurs as a result of mutations in genes that are essential to growth or development. They can cause death prenatally or after birth. They may be recessive, dominant or conditional depending on the gene involved. 3/13/2019 17

18. RECESSIVE LETHAL ALLELES Expressed only in homozygous condition Heterozygous is not affected Example is seen in Sickle cell Anemia, Manx cat. 3/13/2019 18

19. DOMINANT LETHAL ALLELES They are expressed in both homozygous and heterozygous condition It requires the present of only one allele in the organism to be fatal. It is not usually found in population because, it usually result in the death of the organism before it can transmit its lethal gene on to its offspring. Example : Huntington’s disease. 3/13/2019 19

20. CONDITIONAL LETHAL ALLELE Allele that will only be fatal in response to some environmental factors. Example: Favism 3/13/2019 20

21. SEX LINKED TRAIT Also known as “X-linked Red-green colorblindness is a recessive trait linked to the X- sex chromosome X C = normal color vision X c = color blindness Y (doesn’t code for color-seeing) 3/13/2019 21

22. Hemophilia is a sex-linked recessive trait d isorder where individuals are missing the normal blood clotting protein. Uncontrolled bleeds from minor cuts or bruises. 3/13/2019 22

23. MUSCULAR DYSTROPHY X-linked recessive trait Progressive weakening and loss of skeletal muscle. Defective version of gene that codes for muscle protein 3/13/2019 23

24. SEX LIMITED TRAIT Sex limited characteristic is encoded by autosomal genes that are expressed in only one sex. Both males and females possess sex limited genes and transmit them to their offspring. Usually influenced by sex hormones like estrogen, testosterone „Breast development is normally limited to females Beard growth is normally limited to males 3/13/2019 24

25. SEX INFLUENCED TRAIT Traits where an allele is dominant in one sex but recessive in the opposite sex . Example: Pattern baldness in humans caused by an autosomal gene „Allele (dominant in males, but recessive in females) 3/13/2019 25

26. PENETRANCE Penetrance is the proportion of people with a specific genotype who manifest a particular clinical characteristic or phenotype. 3/13/2019 26

27. INCOMPLETE PENETRANCE Occurs when a dominant allele is not always expressed in the phenotype of the individual. Example: Polydactyl, the condition of having extra fingers or toes. Peavy , 2007 3/13/2019 27

28. EXPRESSIVITY Expressivity is the series of signs and symptoms that occurs in different people with the same genetic condition. The number of digits can vary in polydactyl. high expressivity: a person with several extra digits. low expressivity: a person with single extra digit. Peavy , 2007 3/13/2019 28

29. REFERENCES Hartl, D. L., & Jones, E. W. (1998). Genetics: Principles and Analysis 4th ed . Jones and Bartlett Publishers Lobo, I. (2008). Mendelian ratios and lethal genes. Nature Education , 1(1), 138. Miko , I. (2011). Gregor Mendel and the principles of inheritance . Nature Education (1). Peavy , T. (2007). Extension to Mendelian Genetics. Pierce, B. A. (2012). Genetics: A conceptual approach. Macmillan Watson J. and Crick F.(2015).Genetics and evolution. Chapter 5;Principle of inheritance and variation; Pages 72-94. 3/13/2019 29