Human Karyotypes Karyotypes = pictures of homologous chromosomes lined up during metaphase 1 23 pairs of chromosomes (1 set from the mother & 1 set from the father) - - 22 pairs are autosomes 1 pair is sex chromosomes XX = female ♀ & XY = male ♂ About Chromosomes Chomosomes = structures of tightly coiled chromatin (DNA) Homologous chromosomes = chromosomes of same size & shape carry the same genes for the same traits Chromosomal Theory of Inheritance “Genes are located on chromosomes” Genes - are hereditary units of DNA control characteristics & abnormalities exist in different forms called alleles ALLELES Dominant – shows Recessive – shows whenever present - designated w/capital letters T = tall - - only if the organism is homozygous masked w/dominant alleles designated w/lowercase letters t = short GENOTYPE = genetic makeup HOMOZYGOUS (Pure) - organism has 2 identical alleles for a trait TT or tt HETEROZYGOUS (hybrid) - organism has 2 different alleles for a trait Tt PHENOTYPE Physical appearance an organism develops as a result of its genotype Phenotype Pure tall plant Genotype Pure short plant Hybrid tall plant tt (homozygous recessive) Tt (heterozygous) TT (homozygous dominant) Mendel’s Peas