Meiosis and Heredity

• Meiosis ensures the formation of haploid gamete cells in sexually reproducing diploid organisms
• Diploid: a body cell that has two full pairs of chromosomes (one from each parent) that differ in size, shape, genetic information, and centromere location
• Haploid: a cell that contains one set of chromosomes, ex. gametes
• Two haploid gamete cells come together in sexual reproduction to produce a diploid cell
• Prophase I: the nuclear envelope begins to disappear, fibers begin to form, DNA coils into visible duplicated (or double) chromosomes made up of sister chromatids, and double chromosomes pair up based on size, shape, centromere location, and genetic information. While paired, chromatids exchange genetic information with chromatids from the other chromosome (non-sister chromatids exchange genetic information)
• Metaphase I: double chromosomes remain in pairs and fibers align pairs across the center of the cell
• Anaphase I: fibers separate chromosome pairs and each double chromosome from the pair migrate to opposite sides of the cell
• Telophase I: the nuclear envelope reappears and establishes two separate nuclei, each nucleus contains only one double chromosome from each pair, nucleus only contains half of the total information the parent nucleus contained, and chromosomes will begin to uncoil
• Cytokinesis I: the two daughter cells are divided
• Prophase II: nuclear envelope begins to disappear and fibers begin to form
• Metaphase II: fibers align double chromosomes across the center of the cell
• Anaphase II: fibers separate sister chromatids and chromatids (single chromosomes) migrate to opposite sides of the cell
• Telophase II: nuclear envelope reappears and establishes separate nuclei, each nucleus contains single chromosomes, and chromosomes will begin to uncoil
• Cytokinesis II: separates the two cells into four daughter cells
• Daughter cells are haploid and genetically different from each other and parent cell
• Crossing over increases genetic diversity among gametes
• Crossing over occurs in prophase I of meiosis I and it is where nonsister chromatids of double homologous chromosomes exchange segments; results in recombinant chromatids and the formation of recombinant chromatids increases genetic diversity
• Random assortment of chromosomes serves to increase variation
• The order of homologous pairs during metaphase I affects which chromosomes end up in each gamete and different combinations of chromosomes in each gamete increase genetic variation
• Fertilization of gametes serves to increase variation
• Transmission of genetic information from one generation to the next provides for continuity of life 
• Mendel’s laws describe the inheritance of genes and traits on different chromosomes
• A gene is a unit of heredity coding for a trait and can be transferred from one generation to the next
• A trait is a genetically determined characteristic of an organism
• An allele is a specific variation of a gene
• Dominant allele - always shows in the phenotype if inherited (uppercase letter)
• Recessive allele - only shows in the phenotype when the dominant allele has not been inherited (lowercase letter)
• Law of segregation: chromosomes carry alleles (homologous chromosomes carry alleles for the same trait ); when chromosomes are separated into daughter cells during meiosis, the alleles for each trait are also separated. The separation of these alleles allows for genetic variation among gametes
• Law of Independent Assortment: two or more genes assort independently of each other, one trait is not automatically inherited with another trait, and alleles for separate traits can be packaged in every possible combination into gametes
• A monohybrid cross is an examination of how one trait is inherited 
• A dihybrid cross is an examination of how two traits are inherited
• Null Hypothesis (H) - States there is no relationship or no difference between two groups of data in an investigation
• Alternative Hypothesis (HA) - One of many possible hypotheses that state observed results are due to a nonrandom cause
• Chi-squared goodness-of-fit test: used to determine if there is a significant relationship between two groups of data, observed outcomes are compared to expected outcomes to see if variations could be due to chance, often used to test genetic crosses; can also be used for other analyses
• Linked Genes: Genes that are adjacent and close to one another on the same chromosome and that are inherited together
• Sex-linked traits: traits that are determined by genes located on sex chromosomes
• Genes that are adjacent and close to one another on the same chromosome may appear to be genetically linked and are typically inherited together and are less likely to be separated during crossing over in meiosis
• Map distance: tells you how close together a pair of linked genes is and is determined by how frequently a pair of genes participates in a single crossover event
• The probability that genetically linked genes will segregate as a unit can be used to calculate the map distance between them (ex. if a pair of linked genes has a recombination frequency of 5%, they are close together on the chromosome and are considered 5 map units apart)
• Sex-linked traits deviate from Mendel's model of inheritance