Chapter E4.1 Living things inherit traits in patterns.

Parents and offspring are similar. Some traits inherited from parents Some traits acquired by learning or affected by environmental influence Some combine both influences.

Genes are on chromosome pairs. Gene=a unit of heredity a segment of DNA carries a code for a particular trait or function occupies a specific place on a chromosome Most functions and traits are coded for by more that one gene.

Humans Have 23 pairs of chromosomes ( a homolog from each parent) Homologs may have same or different alleles (variants of a gene) Human Females—have two X-chromosomes Human Males—one X-and one Y-chromosome

Gregor Mendel made some important discoveries about heredity. Experiments with pea plants—each parent contributes factors of heredity (now known as genes) Genes affect the traits of offspring.

Alleles interact to produce traits. Phenotype=observable characteristics (appearance) Genotype=the set of genes that it has Alleles can be dominant or recessive. Only one allele is necessary for a trait to be expressed if the allele is dominant. If alleles are recessive, two recessive alleles must be present for the trait to be expressed.