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# Introduction to Genetics ## Chapter 17 ### The Y Chromosome - The Y chromosome is much shorter than the X and is carried only by males. - A child inheriting two X chromosomes (XX) is female, while a child inheriting an X from the mother and a Y from the father (XY) is male. ### Structure of Chr...

# Introduction to Genetics ## Chapter 17 ### The Y Chromosome - The Y chromosome is much shorter than the X and is carried only by males. - A child inheriting two X chromosomes (XX) is female, while a child inheriting an X from the mother and a Y from the father (XY) is male. ### Structure of Chromosomes - Chromosomes are made of a tightly coiled strand of DNA, along with supporting proteins called histones. - There is a total length of about 2 meters of DNA in each body cell. - During replication, the telomere is shortened, which can damage the chromosome. This is repaired by an enzyme called telomerase. ### Genes - About 99% of the cell's DNA does not code for protein, referred to as filler DNA. - DNA sequences that code for proteins are referred to as genes; the human genome contains about 20,500 genes. - Genes typically exist in pairs, with one gene on each chromosome in the pair. ### DNA Structure - DNA is a double-stranded molecule made up of two chains of nucleotides, which consist of a sugar, a phosphate group, and a base. - The DNA molecule resembles a twisted ladder, where: - The uprights are formed by alternating chains of sugar and phosphate. - The bases link to the sugars, forming the rungs of the ladder. ### Bases in DNA - Four bases found in DNA: - Adenine (A) - Guanine (G) - Thymine (T) - Cytosine (C) - Bases are arranged to allow for protein synthesis, following complementary base pairing rules. ### Mitochondrial DNA - Each cell contains, on average, 5000 mitochondria holding mitochondrial DNA, important for energy production. - Mitochondrial DNA is inherited from the mother, resulting in specific patterns across generations. ### Mutation - A mutation refers to a heritable alteration in the genetic makeup of a cell. - Mutations can occur spontaneously due to errors in DNA replication and cell divisions. ### Figure 17.3 - Depicts Deoxyribonucleic acid (DNA) with labeled strands and bases. --- Page Reference: 477