4: Mendelian Genetics
- Page ID
- 171256
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- 4.1: Alleles and genes
- Genes as DNA instructions located on chromosomes, with alleles as alternative versions of the same gene. Clear links between allelic differences and observable traits, using simple, concrete examples.
- 4.2: Mendel’s First Law
- Equal segregation of paired alleles during formation of eggs and sperm, so each gamete carries one allele at random. Genotypes described as homozygous, heterozygous, or hemizygous, and recognition that populations can hold many alleles, both wild type and mutant.
- 4.3: Mendel and his peas
- Mendel’s focused questions, trait choices, and careful counting that revealed consistent patterns. The historical path from overlooked findings to recognition, and why peas made inheritance patterns easy to detect.
- 4.4: The law of segregation
- Connections between genetic makeup and visible traits, with predictions for F1 and F2 generations. Use of simple 2 by 2 grids and test crosses to infer genotypes and explain dominant and recessive outcomes.
- 4.5: The law of independent assortment
- Independent transmission of genes on different chromosomes, with dihybrid predictions that yield the classic 9:3:3:1 ratio. Noting linkage as a key exception when genes sit close together.
- 4.6: Relationships Between Genes, Genotypes and Phenotypes
- Meanings of locus, genotype, and phenotype, and how environment can shape expression. Clear contrasts among complete dominance, incomplete dominance, and codominance, illustrated with familiar examples such as flower color and ABO blood types.
- 4.7: Worked example - Punnett squares
- Stepwise problem solving with Punnett grids combined with product and sum rules. Practice that covers one and two traits, plus patterns like incomplete dominance, codominance, and multiple alleles.
- 4.8: Biochemical Basis of Dominance
- Why one working copy of a gene often produces enough product for a normal result (haplosufficiency), and when one copy is not enough (haploinsufficiency). Cases where mutant alleles create new activities and novel phenotypes.
- 4.9: Crossing Techniques Used in Classical Genetics
- Planned matings that reveal inheritance, including true breeding lines, reciprocal crosses, and test crosses. Model organisms such as fruit flies that make patterns clear, and how these tools connect with later molecular approaches.
- 4.10: Probabilities in genetics
- Efficient predictions for genetic outcomes using the product rule for independent events and the sum rule for exclusive events. Strategies that replace oversized grids for multigene problems and highlight frequencies such as recessive homozygotes.