Inheritance in biology Introduction to genetics

red hair recessive trait.

genes pieces of dna contain information synthesis of ribonucleic acids (rnas) or polypeptides. genes inherited units, 2 parents dividing out copies of genes offspring. process can compared mixing 2 hands of cards, shuffling them, , dealing them out again. humans have 2 copies of each of genes, , make copies found in eggs or sperm—but include 1 copy of each type of gene. egg , sperm join form complete set of genes. resulting offspring has same number of genes parents, gene 1 of 2 copies comes father, , 1 mother.

the effects of mixing depend on types (the alleles) of gene. if father has 2 copies of allele red hair, , mother has 2 copies brown hair, children 2 alleles give different instructions, 1 red hair , 1 brown. hair color of these children depends on how these alleles work together. if 1 allele dominates instructions another, called dominant allele, , allele overridden called recessive allele. in case of daughter alleles both red , brown hair, brown dominant , ends brown hair.

although red color allele still there in brown-haired girl, doesn t show. difference between see on surface (the traits of organism, called phenotype) , genes within organism (its genotype). in example can call allele brown b , allele red b . (it normal write dominant alleles capital letters , recessive ones lower-case letters.) brown hair daughter has brown hair phenotype genotype bb, 1 copy of b allele, , 1 of b allele.

now imagine woman grows , has children brown-haired man has bb genotype. eggs mixture of 2 types, 1 sort containing b allele, , 1 sort b allele. similarly, partner produce mix of 2 types of sperm containing 1 or other of these 2 alleles. when transmitted genes joined in offspring, these children have chance of getting either brown or red hair, since genotype of bb = brown hair, bb = brown hair or bb = red hair. in generation, there therefore chance of recessive allele showing in phenotype of children—some of them may have red hair grandfather.

many traits inherited in more complicated way example above. can happen when there several genes involved, each contributing small part end result. tall people tend have tall children because children package of many alleles each contribute bit how grow. however, there not clear groups of short people , tall people , there groups of people brown or red hair. because of large number of genes involved; makes trait variable , people of many different heights. despite common misconception, green/blue eye traits inherited in complex inheritance model. inheritance can complicated when trait depends on interaction between genetics , environment. example, malnutrition not change traits eye color, can stunt growth.

inherited diseases

some diseases hereditary , run in families; others, such infectious diseases, caused environment. other diseases come combination of genes , environment. genetic disorders diseases caused single allele of gene , inherited in families. these include huntington s disease, cystic fibrosis or duchenne muscular dystrophy. cystic fibrosis, example, caused mutations in single gene called cftr , inherited recessive trait.

other diseases influenced genetics, genes person gets parents change risk of getting disease. of these diseases inherited in complex way, either multiple genes involved, or coming both genes , environment. example, risk of breast cancer 50 times higher in families @ risk, compared families least @ risk. variation due large number of alleles, each changing risk little bit. several of genes have been identified, such brca1 , brca2, not of them. however, although of risk genetic, risk of cancer increased being overweight, drinking lot of alcohol , not exercising. woman s risk of breast cancer therefore comes large number of alleles interacting environment, hard predict.