The Human Genome Chapter 14

Human Chromosomes Karyotype—picture of paired homologous chromosomes Humans have 46 chromosomes 2 of those are sex chromosomes (X or Y) Females have XX; Males have XY The remaining 44 are called autosomes.

Gametes All egg cells contain 22 autosomes and 1 X. 50% of sperm contain 22 autosomes and 1 X; the other 50% contain 22 autosomes and 1 Y The sperm determines the sex of the offspring!

Human Traits Pedigree Chart—shows relationships within a family; can be used to determine how a trait is passed from one generation to the next Many traits are polygenic Many traits are influenced strongly by environmental factors Environmental effects on gene expression are not inherited The gene may be expressed in a later generation under the right conditions

Human Genes The human genome contains tens of thousands of genes. Example: Chromosome 22 is one of the smallest human autosomes. 22 contains approximately 43 million DNA bases and contains as many as 545 different genes. Many human traits are controlled by more than one gene (polygenic) or have incomplete or co-dominant alleles.

Blood Typing ABO blood groups Controlled by a gene that codes for a hemoglobin protein, either A, B, or none The protein is what makes different blood types incompatible A & B are co-dominant O is recessive Rh factor—controlled by an additional gene, Rh+ is dominant; Rh- is recessive

Sex-Linked Genes Genes that are located on either the X or Y chromosome are called sex-linked. The X chromosome is much larger and contains hundreds more genes than the Y. Males have just one X chromosome. All X-linked alleles are expressed in males, even if they are recessive. Examples: Colorblindness, Hemophilia, and Muscular Dystrophy

X-chromosome Inactivation In females, one X chromosome is randomly switched off. It is called a Barr body. Different cells can switch off different X chromosomes. Example: All calico cats are female. Their patches of different colors are controlled by different X chromosomes. Male cats can have only one color of spots because they have only one X chromosome.

Chromosomal Disorders The most common error in meiosis occurs when homologous chromosomes fail to separate. This is called nondisjunction. If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes and a chromosomal disorder may result. Example: Down Syndrome (trisomy 21), Turner’s syndrome, and Klinefelter’s syndrome

Human Genetics DNA fingerprinting—a tool that analyzes sections of DNA that vary widely from individual to individual The Human Genome Project—started in 1990, scientists from around the world successfully mapped and sequenced all human DNA by the end of 2000. Gene Therapy—process of changing the gene that causes a genetic disorder. An absent or faulty gene is replaced by a normal, working gene.