Heredity Review Chapters 13-15

Genes Segments of DNA that code for a protein Locus is the location of a gene on the chromosome Autosomes: body chromosomes 1-22 Sex chromosomes: X and Y

Meiosis Reduces chromosome number in half (diploid to haploid) Meiosis I homologous chromosomes separate Meiosis II sister chromatids separate

Meiosis is Special Crossing over: regions of homologous chromosomes overlap and exchange DNA Makes 4 genetically different cells Occurs only in sex organs Gonads make gametes

Mendel’s Laws Independent Assortment: each homologous chromosome is divided into gametes randomly Segregation: each gamete gets one copy of each allele as they separate

Genetic Diversity Independent assortment of chromosomes creates different gametes (223) Crossing over changes chromosomes’ genes (2-3 times per chromosome) Random fertilization

Mendelian genetics Dominant vs. recessive Homozygous vs. heterozygous P vs. F generation Genotype vs. phenotype Codominance vs. incomplete dominance Monohybrid vs. dihybrid cross

Testcross To find the genotype of a dominant phenotype: Cross it with a homozygous recessive If any offspring are recessive, unknown was heterozygous If all were dominant, unknown was homozygous dominant

Interesting genetics… Pleiotropy: one gene, many effects Polygenic inheritance: many genes, one effect Epistasis: one gene controls the expression of another

Pedigrees Aka family trees Guys = square; ladies = circles Shaded = has the condition, ½ shaded means carrier, no shade means normal It allows you to identify genotypes by tracing phenotypes

Common genetic disorders Albinism, cystic fibrosis, Tay-Sachs, sickle cell anemia are all recessively inherited Achondroplastic dwarfism, Huntington’s are dominant Heart disease, diabetes, cancer are polygenic

Morgan Discovered gene linkage Linked genes occur on the same chromosome and are inherited together Genetic maps: determine order of genes based on crossing over frequencies

Sex-linked disorders Duchenne muscular dystrophy Hemophilia Red-green colorblindness All x-linked

Barr body One of female’s X chromosomes super condenses and is rarely used

Nondisjunction When chromosomes do not separate properly; they remain attached Some gametes get more, some less Trisomy 21 (Down syndrome) Trisomy 18 (death) Aneuploidy vs. polyploidy

Genomic imprinting Paternal and maternal chromosomes have special marks (methyl groups) Some disorders arise only from paternal or maternal chromosomes Prader-Willi = dad (retardation, obesity, short) Angelman = mom (uncontrollable laughter, jerky movements)