Living things inherit traits in patterns Parents and offspring are similar Characteristics (eye color, height, etc.) are also known as traits Some traits are inherited, others (like riding a bike or reading) are acquired during your life You may have inherited similar traits to your parent(s) traits

Genes are on chromosome pairs A GENE is a unit of heredity that occupies a specific location on a chromosome and codes for a particular product. Segments of DNA on a chromosome HEREDITY is the passing of genes from parents to offspring Individuals inherit genes from their parents The genes code for the expression of traits In most eukaryotes (multi-cellular organisms) cells contain pairs of chromosomes with one chromosome from each pair coming from each parent

Variations of the same gene (brown eyes/blue eyes) are called ALLELES For each gene pair one allele comes from the mother, one from the father. Each member of a gene pair helps determine a specific trait. Each species has a characteristic number of chromosomes Humans have 23 pairs, for a total of 46 chromosomes Human chromosomes are numbered 1-22, with the 23rd pair are the sex chromosomes Sex chromosomes are the X chromosome and Y chromosome, they are responsible for determining gender!! Human females have 2 X chromosomes (XX) Human males have an X chromosome and a Y chromosome (XY)

Genotype and Phenotype An organism’s phenotype describes the actual characteristics that can be observed: for example blue eyes, size of your feet etc. Physical appearance. An organism’s genotype is the name for the genes an organism has. Your genotype is not always obvious from your phenotype. Gene make up.

Dominant and Recessive When representing the genetic makeup (genotype) of an organism, upper case and lower case letters are used; two letters total for each trait. Alleles can be either dominant or recessive. A dominant allele is the one that is expressed in the phenotype even if only one copy is present in the genotype A recessive allele is one that is expressed in the phenotype only when two copies of the allele are present

Dominant and Recessive cont’d Dominant alleles are represented by a capital letter Recessive alleles are represented by a lower case letter Let’s use the letter Y for yellow seeds: Y would represent a dominant allele y would represent a recessive allele

Y would represent a dominant allele y would represent a recessive allele There need to be 2 letters to represent the trait (one from each parent) The choices are: YY or Yy or yy (This is the genotype) YY would be 2 dominant alleles Yy is one dominant and one recessive allele yy is two recessive alleles What are the phenotypes of these choices?