Genetic Variation and Change

Independent Assortment: Independent Assortment is the random separation of homologous chromosomes during meiosis 1. Independent Assortment is when homologous chromosomes line up in random along the cell center. Spindle Fibers attack to the chromosomes and pull apart at random into one of two daughter cells. Each daughter cells will end up with a random selection of chromosomes and alleles.

Segregation of Alles: Segregation is the independent assortment of alleles on different chromosomes. Segregation is the separation of homologous pairs into the gametes. Genetic Variation occurs as each new gamete has different alleles. Segregation is where homologous chromosomes are pulled apart and separated. Only one chromosome from each pair is separated.

Crossing Over is when duplicated chromosomes pair up and pairs of the chromosomes can cross over one another at a point called a chiasma. This allows for genetic information to be exchanged allowing for unique chromosomes with new combinations of alleles. Crossing over is the swapping of DA segments between non sister chromatids of homologous pairs.

Co Dominance is when two different alleles for a particular is expressed in a heterozygous individual rather than one being dominant and one being recessive. This means that both phenotypes are physically expressed, and they do not blend.

Incomplete Dominance is similar to Co Dominance however the two phenotypes blend, creating an intermediate phenotype.

Multiple Allelism is when 3 or more alleles are present for a particular genetic trait. Although an individual can only have 2 alleles for each genetic trait (one from each parent). However, there can be many of alleles of that genes present in the wider population. This can be good for increasing genetic variation.

Lethal Alleles are alleles that if present will cause the premature death of an individual. Lethal Alleles are usually present in a homozygous form. Lethal Alleles are usually recessive meaning that for the lethal allele to be present two copies of the allele are needed, one from each parent.

The expected phenotypic for a normal dihybrid cross when crossing two heterozygous individuals 9:3:3:1.

Linked Genes are genes located on the same chromosomes. Genes located on the same chromosome are more likely to be inherited together during crossing over. Two genes located on different chromosomes are likely to be separated during meiosis. Linked genes can however be separated however it is unlikely. Linked genes can change the expected phenotypic ratio

Meiosis is a type of cell division that reduces the chromosome number by half, creating genetically unique daughter cells. During sexual reproduction they fuse together to form a full zygote with the correct number of chromosomes. There are two stages of Meiosis, these are Meiosis 1 and Meiosis 2.

PMAT1 (Meiosis I)

  1. Prophase I: Homologous chromosomes pair up and exchange genetic material through crossing over.

  2. Metaphase I: Paired chromosomes (tetrads) align at the cell's equator.

  3. Anaphase I: Homologous chromosomes separate and move toward opposite poles.

  4. Telophase I: Two new cells form, each with half the original chromosome number, but chromosomes are still duplicated.

PMAT2 (Meiosis II)

  1. Prophase II: Chromosomes condense again in the two newly formed cells.

  2. Metaphase II: Chromosomes line up individually along the equator.

  3. Anaphase II: Sister chromatids separate and move to opposite poles.

  4. Telophase II: Four haploid cells result, each with a single set of chromosomes, forming gametes.

The key purpose of Meiosis is to generate genetic variation which is essential for evolution

Gene Pool is all the different alleles present in a breeding population.

Allele frequency is how frequent a gene occurs in a gene pool

Gene Flow refers to migration. Migration is the movement of individuals, if those alleles are not present in the new populations gene pool it creates genetic variation.

Genetic Drift is the random change in the allele frequency due to random chance and random events. Genetic Drift Affects small populations the most

Founder Effect is when a group of individuals leaves one population and moves to a different place which is usually isolated (such as an island). This reduces genetic variation, and mutations are the only source of genetic variation. After 1000’s of years the new population will look nothing like the founding population.

Genetic Bottleneck is the sudden drop in population size, resulting in a loss of biodiversity. Genetic Bottleneck can be caused by things like massive weather events e.g. a tornado. A bottlenecked population is more vulnerable to genetic drift