Extensions of Mendelian Genetics

1. Extensions of Mendelian Genetics

2. Sex determination • In humans and many other organisms, sex is determined by the ___________________. • Sons get their X-chromosome from their ___________ only. • Fathers must pass their X-chromosome to their _________. X and Y chromosomes mothers daughters

3. X- linked Traits • Genes that are found on the X chromosome follow a have a special pattern of inheritance: • X-linked traits are never passed from father to _____. son

4. Males are much more likely to be affected than females. If trait is recessive, daughters have a second X chromosome so they can be heterozygous. Sons only have one X chromosome and are called __________ for that trait. hemizygous

5. carriers • Daughters can be ________ and pass the trait to their sons. • For example: Color blindness, hemophilia (ineffective blood clotting)

9. Codominance alleles • When two different _________ are present, both alleles are expressed. • Neither trait is recessive, so different letters are used to represent each allele.

10. For example: blood type. • Red blood cells are coated with different _________________. • Each person contains either A, B, A and B or neither protein. marker proteins

11. Multiple Alleles: more than 2 alleles

12. Codominance: Sickle cell There are threephenotypes Normal Normal individuals have two normal hemoglobinalleles Sickle cell anaemia, a severe form where all the red blood cells are affected. Sickle cell anemiapatients have two sickle cell alleles in their genotype Sickle cell trait, a mild condition where 50% of the red blood cells are affected. Sickle cell trait individuals are heterozygotes, having one of each allele

13. Incomplete Dominance • Heterozygote results in blending of traits • Ex: carnations: red x white  pink

14. Polygenic Traits • A characteristic that is affected by more than one gene. • Alleles are ______ or ________. • Active alleles are __________. • Results in a ________ of phenotypes, not just 2 different phenotypes. active inactive additive range

15. For example hair color. • In general, human hair color is determined by two color pigments, ____and ______. red brown

16. converted A gene controls whether the red pigment is __________ to the brown pigment. • RR: almost all red pigment is converted to brown. • rr: red pigment is NOT converted to brown.

17. Other genes control HOW MUCH pigment is made. • HHHHHHHH: If all genes are _______ then hair is ______. • hhhhhhhh: If all genes are ________ then hair is _______. • There is a range of hair colors depending on how many genes are active. active dark light inactive

18. More examples: • Skin color, height • Diseases: cancer, diabetes

19. Other inheritance patterns for genetic disorders- recessive • Cystic Fibrosis: • Cystic fibrosis transmembrane conductance regulator protein (CFTR) • Creates mucus that clogs lungs and pancreas • Tay-Sachs: • Mutation in gene for an enzyme in lysosome allows waste to build up • Deterioration of central nervous system and death in early childhood

20. Other inheritance patterns for genetic disorders- dominant • Dwarfism (Achondroplasia): • Failure of bones to grow due to a mutation or inherited mutation in the fibroblast growth factor receptor 3 gene • One copy of the gene results in dwarfism, two copies of the mutated gene is fatal