University:
High School
Course:
High School Genetics
Academic year:

2023
Views:

321

Pages:

18
Author:

Dave D.

Causes of Variation Variation ⦿ Variation: small differences in a population Causes of Variation #1: Meiosis ⦿ Meiosis – crossing over & independent assortment Causes of Variation #2: Mutations ⦿ Mutation: a permanent change in the sequence of DNA (GCAT) • Causes: ●Errors during DNA Replication (S Phase) ●Environmental Factors – sunlight, radiation, smoking Mutations! Rare all-‐black penguin mutation. “This large whippet is named Wendy and she has something called “double muscling”, causing her to have much higher muscle mass than her lithe counterparts. Included in these photos are a few typical whippets to use as comparison. Wendy is friendly and by all accounts, happy, but if there’s ever a hulk television show starring dogs… we know who to cast.” ⦿ Mutations can be • BENEFICIAL – antibiotic resistance (good for bacteria NOT humans) • HARMFUL – Cystic Fibrosis • NEUTRAL ⦿ Passed on to offspring if they occur in gametes Mutations Can be “good” and “bad” – Sickle Cell Anemia Mutations & DNA Replication ■ Point Mutation: The substitution of a single nucleotide. Can be a missense or nonsense mutation. ■ missense – substitution of one nucleotide causes one amino acid to change ■ nonsense – codes for a premature stop Sickle Cell Anemia is caused by a point mutation. ■ Frameshift Mutation: ■ A type of point mutation when the addition or deletion of a single nucleotide causes the codons to be incorrectly grouped or shift. ■ If this type of mutation occurs near the beginning of a gene, it will prevent many codons from coding for the proper amino acids. Example of a substitution mutation… Original: Point Mutation: The fat cat ate the wee rat. The fat rat ate the wee rat. Example of a frameshift mutation… Original: Frameshift: The fat cat ate the wee rat. The fat caa tet hew eer at. (the “t” was deleted completely) Silent Mutations • Silent mutation – substitution mutation but will code for the same amino acid as “normal” DNA. ● In other words, the protein looks like no mutation is present, but the DNA tells otherwise. Causes of Variation #3: Mutations caused by environmental factors ⦿ Environmental mutations are caused by exposure to mutagens ⦿ Mutagen – any physical or chemical element that can induce a change in the DNA ⦿ Mutagens include – radiation, chemicals in food, drugs, alcohol, skin products Types & Sources of Mutagens “Frog mutations are not typically very cute, and they’re often correlated quite directly to pollution. While frogs don’t seem to mind having a few extra limbs here or there, it’s more disturbing when one knows the source of their discomfort and strange formation.” Are Environmental Mutations Inheritable? ⦿ Environmental mutations can lead to • Cancer • Birth Defects • Extra Limbs ⦿ NOT ALL mutations will be passed down unless they occur during sex cell formation * mom and baby are being exposed to smoke. Any mutations that result will not be passed down unless the mutation affects the sex cells that are forming in the baby. Damage to these can affect the grandchildren of this pregnant mom and thus be passed down.