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Non-Mendelian Genetics

Non-Mendelian Genetics. Complete dominance Law of segregation Law of independent assortment One gene  one trait. Mendelian Genetics. Codominance Incomplete dominance Multiple alleles Pleiotropy Epistasis Polygenic inheritance Sex-related inheritance. Non-mendelian Genetics.

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Non-Mendelian Genetics

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  1. Non-Mendelian Genetics

  2. Complete dominance • Law of segregation • Law of independent assortment • One gene  one trait Mendelian Genetics

  3. Codominance • Incomplete dominance • Multiple alleles • Pleiotropy • Epistasis • Polygenic inheritance • Sex-related inheritance Non-mendelian Genetics

  4. One gene, many phenotypic effects Pleiotropy (pleion, “more”)

  5. http://3.bp.blogspot.com/-bUvXE8h_wuE/TycwHFuFqrI/AAAAAAAAA4E/fWfyDR0ETNU/s1600/Phenylketonuria+(PKU).jpghttp://3.bp.blogspot.com/-bUvXE8h_wuE/TycwHFuFqrI/AAAAAAAAA4E/fWfyDR0ETNU/s1600/Phenylketonuria+(PKU).jpg

  6. Two genes affect coat color B  black, b  brown, E  pigment deposited, e no pigment • Effects of one gene are modified by one or several other genes • Examples: • Coat color in mammals • Color of wheat grains • Fruit color in squash • Bombay phenotype in ABO blood groups in man EpistasisOne gene affects expression of another

  7. Bombay phenotype

  8. Quantitative characters vary in a population along a continuum or gradation • Due to the presence of contributory or dominant (ABC) and non-contributory or recessive alleles (abc) • Expression can be affected by environmental factors Polygenic inheritanceAdditive effects of two or more genes on a phenotypic character

  9. Example: • Skin pigmentation controlled by at least three separately inherited genes • Each dark skin allele contributes a unit of ‘darkness’ to the individual • AABBCC  very dark • aabbcc  very light

  10. (very light) (very dark) Aa Bb Cc x Aa Bb Cc (medium brown) brown

  11. Petal length of a plant ranges from 4mm to 12mm to 20mm. Out of 770 plants, only 3 of them have 4mm petals. • How many genes affect petal length? • How many phenotypes are present for petal length? • Give one genotype for a plant with 12 mm petals. • Give two possible genotypes for plants with 6 mm petals • What proportion of plants have 14 mm petals? • What is the phenotype of plants with 7 contributory alleles? • How many contributing alleles does a plant with 8 mm petals have? Polygenic Inheritance Problem Solving

  12. sex is an inherited phenotypic character determined by the presence/absence of certain chromosomes • SRY (sex-determining region of Y) in humans • Sex-linked inheritance • Sex-limited inheritance • Sex-influenced inheritance Sex-related inheritanceexpression of traits is affected by the sex of the individual

  13. Gene linkage – genes located on the same chromosome are inherited together • Sex-linkage • Sex chromosomes contain genes for many characters unrelated to sex • X-linked/Y-linked gene Sex-linked inheritance

  14. Recessive alleles • Color-blindness • Duchenne muscular dystrophy • Hemophilia • Testicular feminization Dominant traits • Hypophosphatemia Examples of X-linked traits

  15. Transmission of genes from father to son • Testis-determining factor (TDF/SRY gene) • Hypertrichosis of the ears Examples of Y-linked (Holandric) Inheritance

  16. involves autosomal genes that are expressed only in either males or females • resulting in a part or function of the body that is present in one sex but not the other • Examples: • milk production • cryptorchidism • feathers in domestic fowl Sex-limited inheritance

  17. dominant in one sex but recessive in the other • autosomal • difference in expression due to the hormonal difference between the sexes • in heterozygotes, the expression of the trait is affected by sex hormones • homozygotes are unaffected and express the trait regardless of the hormone produced Sex-influenced inheritance

  18. pattern baldness • baldness allele is dominant in males but recessive in females • a heterozygous male is bald, but a heterozygous female is not Sex-influenced inheritance

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