Creating Variation Sexual Reproduction & Mutations

Variation ► Variation is the ultimate goal of sexual reproduction. ► Variation allows for a variety of adaptations within a species = survival of the species. = Success. ► Variation is caused by genetic recombination.

Variation

Genetic Recombination ► Basically how organisms recombine their DNA to make another – ie. Sexual reproduction  Includes 4 processes ► 1. Crossing Over ► 2. Random Assortment of Homologous Chromosomes ► 3. Fertilization ► 4. Mutations

Crossing-Over ► When homologous chromosomes swap the same gene.  The mom (maternal) and dad (paternal) genes swap alleles for the same trait.

Original pair Copied for meiosis A mom and dad chromosome swapped genes for the same trait Adds more gamete possibilities

Random Assortment ► Adding to Mendel’s Law of Independent Assortment, Sutton, Bateson, Punnett, and Morgan found that alleles do not separate randomly, but that homologous chromosomes do.  Chromosome Theory of Inheritance

Random Assortment ► With this there is total possible combination of 2 n, where n= the haploid number of chromosomes (# of homologous chromosomes) ► How many then are possible in humans?  8,388,608 – without crossing over

Fertilization ► Union of 2 gametes ► Take the millions of possible gamete types and the requirement that 2 individual unite one of each of their gametes and that increase variation. ► Two of the same coming together is therefore ultimately impossible.

Mutations or Errors ► 3 major types  1. Nondisjunction: Error in separation of chromosomes during Meiosis.  2. Gene Mutation: Affects an entire gene – several nucleotides in length  3. Nucleotide Mutations: Changes in one nucleotide.

Nondisjunction ► Results in either extra or a lack of entire chromosome.

Nondisjunction Scenario ► During Meiosis I the 21 st pair of homologous chromosomes does not separate. ► What is the result? ► What is the disease when the one with and extra chromosomes combines with a normal gamete?

Nondisjunction Scenario ► During meiosis I the 23 rd pair of chromosomes does not separate in a female. ► What is the result? ► What would be the genotype of a child who was composed of the gamete that is lacking the X chromosome with a normal X sperm? ► Disease? ► What would be the genotype of a child who was composed of the gamete with the extra chromosome that is combined with a normal Y sperm? ► Disease?

Gene Mutation ► 4 Types  Deletion: a Gene is deleted  Duplication: 2 copies of a gene  Translocation: Gene moves to a new location  Inversion: 2 genes invert on the same chromosome.

Nucleotide Mutations ► 2 types  1. Frameshift: - missing or extra nucleotide  2. Point: a change in the nucleotide to another type.

Review ► Complete the review sheet provided