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Genetics Since Mendel

Genetics Since Mendel. Unit 9 – Lesson 2 Notes. 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. Incomplete Dominance.

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Genetics Since Mendel

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  1. Genetics Since Mendel Unit 9 – Lesson 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.

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

  5. 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

  6. 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.

  7. Polygenic Inheritance Example

  8. 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.

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

  10. 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

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

  12. 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

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

  14. 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.

  15. Pedigree • A pedigree follows a trait through generations of a family. • Carriers of trait are half shaded. • People with trait are fully shaded. • Squares show males. • Circles show females.

  16. Orange Shows the Trait Who carries the gene? M or F How many people are colorblind?

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