Genetics Since Mendel

1. Genetics Since Mendel Chapter 11 Section 2 Notes

2. Modern Genetics • We know about dominant and recessive genes, now we are going to learn about other types of genetic traits, such as • Incomplete dominance • Multiple alleles • Polygenic Inheritance • Mutations

3. Incomplete Dominance • Neither allele for a trait is dominant. • The phenotype produced is intermediate between the two homozygous parents.

5. Multiple Alleles • More than two alleles are multiple alleles. • Traits controlled by multiple alleles produce more than three phenotypes.

6. Multiple Alleles There are 3 alleles for the gene that determines blood type.(Remember: You have just 2 of the 3 in your genotype --- 1 from mom & 1 from dad). Notice that, according to the symbols used in the table above, that the allele for "O" (i) is recessive to the alleles for "A" & "B". ALLELEIAIBi CODES FORType "A" BloodType "B" BloodType "O" Blood

7. Polygenic Inheritance • A group of gene pairs acts together to produce a trait, which creates more variety in phenotypes. • Many human traits are controlled by polygenic inheritance, such as hair and eye color.

8. Polygenic Inheritance Example

9. Mutations • Mutations – genes that are altered or copied incorrectly. • A mutation can be harmful, beneficial, or have no effect. • Chromosome disorders – caused by more or fewer chromosomes than normal.

10. Mutations • Down syndrome – caused by an extra copy of chromosome 21.

11. Recessive Genetic Disorders Recessive Genetic Disorders • Both parents have a recessive allele responsible for the disorder and pass it on to their child. • Because the parents are heterozygous, they don’t show any symptoms. p P PP Pp Pp pp P Disorder Expressed p

12. Homozygous recessive disorders. PKU Cystic Fibrosis Sickle-Cell Anemia Recessive Genetic Disorders Examples Sickle-Cell

13. Other Genetic Disorders • Genes that determine the sex of an organism are XX in females and XY in males. • Females produce eggs with an X chromosome only. Males produce sperm with either an X or Y chromosome. Y X X X X Y Y X X X EGGS SPERMS

14. Other Genetic Disorders Disorders • Turners Syndrome XO • Triple X Syndrome XXX • Klinefelter syndrome XXY • XYY XYY

15. Sex-linked Disorders • An allele inherited on an X or Y chromosome is a sex-linked gene. • Color blindness is a sex-linked disorder caused by a recessive allele on the X chromosome.

16. Pedigree • A pedigree follows a trait through generations of a family.