Living things inherit traits in patterns

1. 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

2. 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

3. 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)

4. 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.

5. 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

6. 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

7. 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?