5.5 Sources of Inherited Variation

1. 5.5 Sources of Inherited Variation • Darwin’s book “On the Origin of Species” did not answer the question: • Where does the sources of variation of individual traits come from?

2. I.) Mutations • DNA • Found in chromosomes of all cells • Composed of long sequences of 4 nucleotide bases: • Adenine, guanine, thymine, cytosine • Sequence of bases codes for specific inherited traits • Genes are segments of DNA that code for specific traits

3. Mutations • Random changes in DNA sequence in a chromosome • Provide a continuous supply of new information • Caused by: • Environmental factors • Errors while cell is making copies of DNA • Relatively rare in individuals

4. Types of mutations • Neutral mutation • No immediate effect on an individual’s fitness or reproductive success • Most common • Harmful mutation • Reduces an organism’s fitness • Beneficial mutation • Enhances an organisms’ fitness • Provides a selective advantage of others

7. II.) Sexual Reproduction and Variability • Asexual reproduction • Production of offspring form a single parent • Offspring inherit genes of that parent only • Very little inherited variability • Mutations may still occur

8. Sexual reproduction • Production of offspring by the union of sex cells from two different parents • Offspring inherit a combination of genes from both parents

9. 3 reasons for variability among sexually – reproducing individuals • Sexually reproducing species have 2 copies of each gene • Both parents contribute one copy of each gene to the offspring • Offspring has a different combinations of genes from either parent • Unique set of traits

10. 2. Assortment of genes an offspring inherits from either parent is random • The greater the # of genes a species has, the larger the # of combinations and the greater variability of the species as a whole

11. 3. Sexually reproducing species choose different mates • Each combination of parents will give rise to different combinations of genes and traits in the next generation