Chapter 4: Patterns of Heredity

1. Chapter 4: Patterns of Heredity 4.1 Living things inherit traits in patterns 4.2 Patterns of heredity can be predicted 4.3 DNA is divided during meiosis 4.4 Cells use DNA and RNA to make proteins 4.1 Before you learned: Life comes from life Cells contain chromosomes Some organisms reproduce with asexual reproduction 4.1 Now, you will learn: How traits are passed from parent to offspring About discoveries made by Gregor Mendel About dominant and recessive traits

2. Parents and offspring are similar Unique combination of characteristics: “Traits” Inherited traits: Resemble parents: Traits such as hair color, eye color, blood type Acquired traits: developed through your life Leaned behaviors: reading, writing, bike riding Examples that combine both inherited and acquired traits? Musical skills, athletic skills Examples that are not learned but results from interaction with the environment? Skin color How are inherited traits and acquired traits different? Inherited traits are not learned behaviors but are passed from parent to offspring. Eye color is inherited. Acquired traits are learned

3. Genes are on chromosome pairs Inheritance happens through Sexual reproduction: a cell containing genetic information from the mother and a cell containing genetic information from the father combine into a completely new cell, which becomes the offspring Genes are on chromosome pairs Processes are coded for by genes: a unit of heredity that occupies a specific location on a chromosome and code Heredity is the passing of genes from parents to offspring Genes code for the expression of traits Traits are not inherited: the gene code for the trait is. Many genes can code for one trait

4. Genes are on chromosome pairs Cells contain pairs of chromosomes One chromosome of each pair coming from each of two parents Homolog: chromosomes in a pair Sites where specific genes are located Homologous Chromosomes

5. Genes are on chromosome pairs • Specific genes are located • Whether or not a plant is tall is located at place A on a pair of homologs • Both homologs have the gene for height at site A, though the genes may not be identical • Variations: various forms of the same gene are called alleles • The homolog from one parent might have an allele for regular height at site A, the other parent has allele for short height at site A

6. Alleles • Two different forms of the same gene • Humans have 23 pairs of chromosomes = 46 chromosomes • Numbered 1 through 22; 23rd pair = sex chromosomes • Sex Chromosomes: X and Y; Female: XX ; Male = XY

7. Gregor MendelJuly 22, 1822 – January 6, 1884 • Trained in science and math • A monk • Began his study of the inheritance of traits by studying pea plants • Traits: • Plant height, flower and pod position, seed shape, seed color, pod shape, pod color, flower shape • Began with true breeding plants to isolate traits (ones that will always produce offspring with a particular trait when allowed to self-pollinate

8. Mendel: Inheritance • Book’s example: • 1) Mendel began with two true breeding plants: one with regular and one with short heights • Deliberately paired as parents one plant from each set: first generation • Results: all offspring were regular height, the short seemed to have disappeared • 2) Let 1st generation plants self-pollinate: 2nd generation; ¾ were regular height, ¼ short • Short height trait reappeared?!!

9. Mendel: • Suggested each plant must have two “factors” for each possible trait: one from each parent • Some traits could be masked unless both the plant’s factors were for it…such as dwarf height • How many factors or genes does each plant have for each possible trait? • Two

11. Alleles interact to produce traits • Mendels’ plants were single genes, each of which were on a different chromosome • Most traits are controlled by many genes • Phenotype: actual characteristics that can be observed – eye color, height, feet size, eyelid fold • Genotype: genes an organism has.

12. Dominant and Recessive Alleles • Eyefolds and no-eyefolds… • a dominant allele is one that is expressed in the phenotype even if only one copy is present in the genotype – even if the other allele is an alternative form • A recessive allele is one that is expressed in the phenotype only when two copies of it are present on the homologs

13. The Human Genome Project - video • What were some of the strange and unexpected things that scientists discovered when they analyzed the human genome? • Why do scientists compare the DNA of bananas, worms, fruit flies, and humans? How can this information be helpful • Scientists have likened the human genome to a parts list. Explain what they mean. Can you think of another analogy?