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Genotype the combination of alleles carried by an organism phenotype what an organism looks like as a consequence of its genotype 1st Mendel Law Inherited traits are controlled by factors (genes) which occur in pairs (alleles).  1 allele of each gene is present on each homologous chromosome. 2nd mendel law Principle of Dominance and Recessiveness: One factor (gene) in a pair may mask the other or prevent it from having an effect. 3rd mendel law Law of Segregation: The factors (genes) separate when the gametes are formed. Only one factor (gene) from each pair is present in each gamete. 4th mendel law Law of Independent Assortment: Pairs of factors (genes) separate independently of one another to form gametes, and therefore, all possible combinations of factors (genes) occur in the gametes. Example of heterozygous trait ff- has no freckles Example of homozygous trait Ff- has freckles polygenic inheritance 2 or more genes affect the same trait epistasis the ability of one gene to mask/prevent the genetic expression of another gene at a different chromosome locus; EX: albinism (recessive trait) pleitropy the ability of a gene to affect several different characteristics > syndrome: recognizable combination of traits; due to 1 dominant or 2 recessive alleles multiple alleles gene may have three or more alleles * Only two are present in any individual. incomplete dominance inability of either member of an allelic pair to exert dominance, resulting in an intermediate phenotype EX: Caucasians  neither straight nor curly hair is dominant HH' (the hybrid) has wavy hair codominance both members of an allelic pair are dominant & both phenotypes are expressed. EX: blood type AB - genotype IAIB * Do Marfan's Syndrome inability to produce normal connective tissue, resulting in skeletal, eye, and cardiovascular defects 1 dominant allele Genes and the environment * Environment can influence the expression of a gene. EX: Cuttings from parent plant (hydrangea) bloom in different colors according to soil pH EX: Himalayan rabbits & Siamese cats - cooler areas of body are dark X linked gene alleles for body traits which have no counterpart on the Y chromosome. explain why more males are color blind than females X-linked recessive allele For a female to have the disease, her father must have disease & her mother must also have the disease or be a carrier. non disjunction Wrong # chromosomes; happens during Meiosis I and II Turner's Syndrome Nonfunctional ovaries, puberty & menstruation do not occur, lack of breast development, stocky build, & tendency toward learning problems (Estrogen treatment can promote physical development.) - Increased risk of health problems such as cardiovascular disease & kidney defects - May show X-linked traits (only 1 X chromosome present) Kleinfelter's Sydrome Testes underdeveloped, some breast development, long limbs, sparse body hair, & may have learning problems but tend to be good with computer skills Trisomy X female XXX (1/1,000 births) - No physical deformities; delayed motor & language development Jacob's syndrome XYY males - taller than average, persistent acne, & tend to have speech & reading problems - high levels of testosterone; some - more aggressive than normal How can X linked traits be identified? -female can only have it if her father has the disease and mother does too or is a carrier. -all infected females will have sons with the same disease -skips a generation. purpose of genetic counseling to see if a couple's child will inherit unfavorable family traits. what causes down-syndrome an extra #21 chromosome sickle cell anemia red blood cells are sickle-shaped, have reduced ability to transport oxygen, & can block circulation * Other complications - jaundice, abdominal and joint pain, damage to internal organs, & poor resistance to infections; usually die by age forty; most common among those of African descent hemophilia bleeder's disease. blood cannot clot. common in children of inbreeding. muscular dystrophy any of several hereditary diseases of the muscular system characterized by weakness and wasting of skeletal muscles