Inheritance

1. Inheritance

2. Traits and Heredity • Trait: any characteristic of an organism • Characteristic: a feature or quality • Organisms get many characteristics from their parents • Heredity is the passing of traits from one generation to another • Organisms inherit traits when parent pass their genetic information (DNA) to their offspring during reproduction

3. DNA, Chromosomes, and Genes • DNA determines what traits are passed from one generation to the next • Deoxyribonucleic acid (DNA) is usually located in the cell nucleus • A molecule of DNA can be very long • To fit inside the nucleus, the DNA wraps around proteins and becomes tightly coiled • These structures that contain the genetic information are called chromosomes • A gene is a segment of DNA that determines a particular trait

4. Genes and Inherited Traits • Genes, or sections of DNA, determine what traits an organism inherits • Genes for a specific trait usually come in pairs • Each gene from the pair is called an allele • Different alleles of the gene produce different results • Offspring receive chromosomes from both parents • Different alleles produce different traits • Can be described in two ways: • Genotype: genes an organism carries represented by letters • Phenotype: an organism’s physical traits

5. Dominant vs. Recessive Traits • Inherited trait: a genetically determined characteristic that gets passed from parent to offspring and that distinguishes one organism from another • Usually, the trait carried by one allele is dominant over the other • Dominant trait: a trait that is always expressed in the phenotype of an organism • If the organism has that allele, it will show that trait • Other alleles are recessive • Recessive trait: expressed only when two recessive alleles are present • If the offspring receives one dominant allele and one recessive allele, the recessive trait is not expressed

6. Dominant and Recessive Traits

7. Inheriting Genotypes • Each pair of genes is a part of an individual’s genotype • The genotypes identifies the alleles that the organism has inherited • Genotypes are written as two letters • Dominant alleles are shown by capital letters • Recessive alleles are shown by lowercase letters • In humans, the allele for free earlobes is dominant over the allele for attached earlobes • So F is used to show the free earlobe allele, and f is used for the attached earlobe allele

8. Inheriting Genotypes • Since each parent contributes an allele for each gene, an offspring can have three possible genotypes • FF, ff, or Ff • Since free earlobes are dominant, the genotypes FF and Ff both result in free earlobe phenotype • Since attached earlobes are recessive, that phenotype appears only when a person has two recessive alleles, ff.

9. LEQs • 1. Where do the differences in traits come from? • Parents’ DNA • 2. Can we predict how inherited traits are passed from parents to their offspring and to the next generation? • Yes