HSC 4555 Lecture Notes - Lecture 3: Genomic Imprinting, Fetus, Polysomy
Document Summary
Human dna is organized into 46 chromosomes (23 pairs). Paired chromosomes look similar under the microscope but differ in dna sequence. One member of each pair is inherited from the mother, and the other from the father. The remaining pair, the sex chromosomes, confers maleness (xy) or femaleness (xx). During meiotic cell division, the chromosomes are distributed to daughter cells. Meiosis results in four daughter cells, each having one-half the normal number of chromosomes (23). Genes that code for a particular trait come in several forms or alleles. Genotype refers to the particular set of alleles an individual receives. People with different genotypes may have similar phenotypes. Some traits involve only one gene locus and are called single-gene traits. The transmission of these traits from parent to offspring follows predictable patterns. The expression of single- gene traits is determined by whether the gene is dominant or recessive. Dominant genes usually code for functional enzymes; recessive genes do not.
