Chapter 16 Questions Describe the work of Gregor Mendel, and how it created the basis of modern transmission genetics. What organism did Mendel use to study genetics, and what did he discover? Mendel used pea plants to discover who the father is. Observed in very short time periods. Mendel used peas and he discovered that certain traits will skip generations and the principle of segregation of alleles and independent assortment of traits. What are genes and alleles? Genes are units of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring. Genes are units of heredity that are transferred from a parent to offspring. Alles are one of two or more alternative forms of a gene. What are dominant and recessive alleles? Dominant alleles are alleles that produce the same phenotype whether it's paired with identical or different allele. Recessive alleles are alleles that does not create a phenotype when a dominant allele is present. A dominant allele are traits that appear if at least one copy of the allele is present. Recessive traits are traits that appear when both alleles present are the recessive allele. Describe the principle of segregation of alleles in transmission genetics. What is the principle of segregation and what is its chromosomal basis? The principle of segregation is described how pairs of gene variants are separated into reproductive cells. (Mendel) The chromosomal basis is the idea that genes are located on chromosomes as well as the behavior of chromosomes. The principle of segregation is in gamete formation the two alleles for a trait segregate and only one is present in the gamete. After fertilization, the zygote has two alleles for each trait, one from each parent. How can a Punnett square be used to predict the expected phenotypic ratio in offspring when considering alleles at one locus? For example, consider two pea plants heterozygous for height that are crossed: Tt x Tt T t T TT Tt t Tt tt This yields the phenotypic ratio of 3 tall and 1 short. Describe the principle of independent assortment of different genes in transmission genetics. What is the principle of independent assortment and what is its chromosomal basis? The principle of independent assortment notes that traits assort independent of each other because nonhomologous chromosomes assort independently in prophase I of meiosis. How can a Punnett square be used to predict the expected phenotypic ratio in offspring when considering alleles at two loci? TtAa (tall plant that has purple flowers) x ttaa (short plant that has white flowers) TA Ta tA ta ta TtAa Ttaa ttAa ttaa ta TtAa Ttaa ttAa ttaa ta TtAa Ttaa ttAa ttaa ta TtAa Ttaa ttAa ttaa 1 tall purple; 1 tall white; 1 short purple; 1 short white Describe how the patterns of inheritance discovered in peas are also seen in other organisms, including humans. How is pedigree analysis used to determine if a trait is dominant or recessive? A dominant trait does not skips a generation, a recessive trait will. Describe the exceptions to the Mendelian rules of inheritance. What is incomplete dominance? An exception to Mendelian inheritance where the heterozygous has a phenotype that is different from the homozygous dominant and the homozygous recessive-usually halfway in between. What is epistasis? Epistasis is where genes at one loci affect the expression of genes at a second loci. What are incomplete penetrance and variable expressivity? Incomplete penetrance and variable expressivity is where the phenotype has different levels of expression in different individuals.