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Chapter 7 Notes Heterozygous (Bb) – the alleles given are both dominant and recessive Homozygous dominant (BB) – the alleles given are both dominant Homozygous recessive (bb) – the alleles given are both recessive Genotype – genetic makeup Phenotype – physical characteristics Monohybrid cross – one trait Dihybrid cross – two traits Autosomes or autosomal chromosomes or body cells – chromosome sets 1-22 Gametes or Sex cells or sperm and egg – chromosome set 23 Section 1 2 copies of each gene is given to the offspring in sexual reproduction Many human genetic disorders are caused by autosomal genes. These can be predicted by using a Punnett square Disorders caused by recessive alleles 2 copies of the recessive allele must be present for a person to have this disorder. This disorder will most often appear in offspring of parents who are both heterozygotes. By being heterozytes, the parent is carrying a normal allele that masks the disease causing recessive allele They are said to be carriers – not showing the disorder but can pass it down o Ex. Cystic fibrosis is a severe recessive disorder that mainly affects the sweat glands and the mucus glands Disorders caused by dominant alleles Far less common than recessive disorders o Ex. Huntington’s disease a nervous system disorder that develops later in life Disorders caused by sex linked traits These are disorders that are linked either to the X or Y chromosome. XX – female XY – male Female can only give an X chromosome to the offspring Male can give either an X or a Y to the offspring Y chromosome only has the trait to determine the male gender X chromosome has many traits o Ex. Colorblindness and sickle cell anemia SECTION 2 Polygenic trait – poly means many genic means genes When several genes influence a trait The genes for this may be on the same chromosome or scattered Ex skin color, eye color, height, weight, hair color Incomplete dominance – an individual displays a trait that is intermediate between 2 parents This is a heterozygous phenotype that is somewhere between the 2 homozygous phenotypes Neither allele is completely dominant or recessive 1 trait is shown Ex. Red flower reproduces with a white flower and you get a pink flower Codominance – when 2 dominant alleles are expressed at the same time Both of the genes give are shown but neither allele is dominant or recessive Ex. Red flowers reproduce with a white flower and you get a white flower with red spots or stripes Sometimes phenotypes are decided by the environment instead of the sum of gene expression Ex. Turtles lay eggs in the sand. If the temperature is warmer the turtles will become females and if it is cooler they will become males Ex twins aren’t always identical SECTION 4 Pedigree – a chart that can help trace phenotypes and genotypes in a family. A family history that shows how a trait is inherited over several generations Like a family tree that shows genetic disease Pedigree tells us where a genetic disorder is found o Autosomal or sex linked (located on the x) o Dominant or recessive o Heterozygous or homozygous Pedigree rules Circle = female Square = male Vertical lines = offspring Read left to right for order of birth Horizontal line = mating Shading indicates disorder o Trait with whole color means it came from homozygous parents o Trait with ½ color ½ not means came from heterozygous parents Another method used to map out the human genes besides the pedigree is the karyotype Karyotype - a picture of all of the chromosomes in a cell Can show chromosomal changes or reveal a loss of a chromosome