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Lecture 12.1 Chromosomes and Inheritance Genes are short segments of DNA that determine our traits Sex chromosomes determine the sex (gender) of an individual and the remaining chromosomes are called AUTOSOMES. Female have XX (sex) chromosomes and 44 autosomes .Males have XY (sex) chromosomes and 44 autosomes.Dads determine the sex of a child, since their sperms can either have an X or Y chromosome. Sex linked genes Genes that exist on the sex chromosomes are called X linked or Y linked. A sex linked trait is coded for by an allele found on a sex chromosome. Because males have only one X chromosome, a male who carries a recessive allele on the X chromosome will have the sex linked trait. Linked Genes These genes are inherited together since they are close to each other on the same chromosome. The further apart the genes are located, the more likely a cross over will occur. Chromosome maps show the position of the genes. Mutations A mutation is a change in the nucleotide base sequence of a gene or DNA. They are constantly being generated in a gene pool. Germ cell mutations occur in the sex cells. They don’t affect the organism, but are passed on to the offspring. Somatic cell mutations occur in the body cells and affect the organism but not the offspring (skin cancer).Mutations can be lethal or beneficial. Chromosome Mutations These are changes in the structure of a chromosome or loss or gain of an entire chromosome. Gene mutations are changes in the nucleotides in a gene. Lecture 12.2 Human Genetics The inheritance of genetic traits can be studied by using a PEDIGREE chart. Squares stand for males and circles for females. A filled symbol means the person has the disease and empty means he does not. A half filled symbol shows they are carriers of the disease. Patterns of inheritance. An autosomal trait shows up equally in males and females. A sex linked trait usually show up in males, and many are caused by recessive genes (color blindness and hemophilia) Polygenic inheritance. This is when many genes control a trait like skin color. Multiple alleles Many genes have more then three alleles,the ABO blood group in humans is an example. X- linked traits These are traits that are carried on the X chromosome ,like color blindness.A pedigree will show many males are affected and no affected female. Sex influenced traits Males and females can show different phenotypes even if they have the same genotype. Male pattern baldness is an example. The high level of testosterone in males is responsible for this. Detecting genetic diseases. Amniocentisis tests a fetus’s fluid for defective disorders. Gene therapy allows us to replace a defective gene with a healthy one.