Mendelian inheritance

• Epistasis: one gene interferes with the expression of another gene
• The Principle of Segregation states that during meiosis, homologous chromosomes separate and each daughter cell receives a unique combination of genes from each parent.
• The Principle of Independent Assortment states that during meiosis, chromosomes line up randomly and independently, meaning daughter cells are equally likely to receive maternal or paternal chromosomes.
• In Mendelian genetics, the offspring of a genetic cross have a unique combination of genes due to the Principle of Segregation and the Principle of Independent Assortment.
• In Mendelian genetics, the parent, gamete, and offspring of a genetic cross can be represented by drawing chromosomes with alleles.
• The principle of independent assortment applies only to genes on different chromosomes due to the independent and random arrangement of homologous chromosomes in metaphase I.
• The principle of independent assortment states that alleles for one gene are inherited independently of alleles for other genes.
• The principle of segregation states that alleles of one gene are separated into gametes.
• Most genes have more than two alleles, for example, ABO blood type has three alleles: A, B, and O, where A and B are codominant and O is recessive to both A and B.
• What phenotype ratios do you predict in the offspring of Ai and Bi parents?
• Codominance is a phenomenon where heterozygotes express both phenotypes separately, for example, in the case of a roan horse, where BB is black and WW is white, but BW is a mixture of black and white hairs.
• Incomplete dominance is a phenomenon where the heterozygote phenotype is intermediate between the homozygote phenotype, for example, in snapdragons, where red and white homozygotes produce a pink heterozygote.
• Asexual reproduction produces genetically identical offspring from one parent.
• Sexual reproduction involves two parents, reproduction by meiosis and fertilization, and offspring have a unique combination of genes.
• In sexual reproduction, somatic cells are diploid cells with 2 sets of chromosomes, and gametic cells are haploid cells with 1 set of chromosomes.
• Homologous chromosomes contain the same genes, one inherited from each parent.
• In humans, each somatic cell has 46 chromosomes, 23 pairs of homologous chromosomes.
• Meiosis reduces the number of chromosome sets from 2 to 1, making 4 haploid daughter cells, and involves two stages of division: Meiosis I: Separation of homologous chromosomes (HCs) and Meiosis II: Separation of sister chromatids (SCs).
• DNA replication occurs before Meiosis I.
• Mendel used true-breeding plants that produced offspring of the same variety when self-pollinated.
• In a Punnett square, the sides represent alleles of sperm/eggs, the middle represents alleles of possible zygotes.
• Genetics is the study of variation and heredity.
• Mendel crossed true-breeding yellow and green seed plants, resulting in an F1 generation with all yellow seeds.
• A Punnett square is used to practice the principle of segregation.
• The principle of segregation also states that the two alleles for a gene separate during anaphase I, when homologous chromosomes are separated.
• The principle of segregation states that individuals have two alleles for each gene, which separate during meiosis, so each gamete only has one allele.
• In meiosis, haploid cells are formed when homologous chromosomes separate during telophase I and are joined together during cytokinesis.
• Nondisjunction is the failure of chromosomes to separate during meiosis.
• Down syndrome results from inheriting three copies of chromosome 21.
• Zygotes and adults have two alleles for each gene, but gametes only have 1 allele for each gene.
• There is no DNA replication between meiosis I and II.
• Gregor Mendel is the father of genetics.
• In Mendel's approach, self-pollinated F1 plants resulted in an F2 generation with approximately 3:1 yellow to green seeds.
• Chromosomes are composed of two sister chromatids during meiosis.
• Mendel concluded that individuals carry two alleles for each gene, which separate during gamete formation, so each gamete only has one allele.
• In Meiosis I, Prophase I involves synapsis where HCs pair up along their lengths and crossing over where exchange of DNA between HCs occurs.
• In Meiosis I, Prophase I also involves chiasmata, locations where crossing over occurred and HCs stay connected.
• In Meiosis I, Metaphase I pairs of HCs are pulled to the center of the cell, held together at chiasmata.
• In Meiosis I, Anaphase I chiasmata break apart and HCs separate toward opposite poles, with SCs still attached at centromere.
• Phenotype refers to observable characteristics or traits.