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Key Concepts
Alleles are different versions of a gene. The genotype is the combination
of alleles in an organism. The phenotype is the way the alleles are
expressed. Inherited traits in the genotype are expressed in the
phenotype. Punnett squares are used to predict the possible allele
combinations in the offspring of parents with known genotypes. They are
used to predict and analyze genotypic and phenotypic ratios and
frequencies. Mendelian genetic crosses include monohybrid (single-trait)
crosses and dihybrid (two-trait) crosses; they can be traced using Punnett
Squares. Non-Mendelian genetic crosses do not follow the same patterns
of inheritance as Mendelian crosses; they include crosses for traits that are
coded for by more than two alleles, or by alleles displaying codominance or incomplete dominance.
In higher organisms, meiosis produces gametes (sex cells) which contain
half the number of chromosomes of the original parent cell (i.e., haploid
cells). Eukaryotic multicellular organisms reproduce sexually by combining
two gametes containing homologous chromosomes (one set of
chromosomes from each parent) during fertilization. Crossing over during
meiosis allows for the reshuffling of genetic combinations between
individual homologous chromosomes in order to produce unique
offspring. Sexual reproduction creates variety in the gene pool because
DNA is inherited from both parents, resulting in new combinations of
alleles.
There are a variety of techniques used to study the genomes of
organisms. DNA fingerprinting is the process of comparing individual DNA
sequences to determine if samples have similar patterns. Genetic
modifications, including transformation by DNA recombinant technology
(plasmids and host bacterial cells), are used to study genetic disorders.
Bioinformatics is the process of using computational techniques to
organize and analyze nucleotide and amino-acid sequences to gain
insights into their functions, origins, and changes over time. DNA and RNA
probes are used in experiments to label nucleic-acid sequences for
chromosomal analysis. Karyotyping stains the chromosomes to visually
analyze them and search for possible genetic disorders.
Fundamental Questions
How are the possible genotypes and phenotypes of offspring predicted?
Why is meiosis significant to sexual reproduction?
What techniques are used to study the genomes of organisms?