Ch. 5 Heredity Life Science

Section 1 – Genetics Learning Objectives 1. Explain how traits are inherited. 2. Identify Mendel’s role in the history of genetics. 3. Use a Punnett square to predict the results of crosses. 4. Compare and contrast the difference between an individual’s genotype and phenotype.

Section 1 – Genetics A. Heredity – the passing of traits from parent to offspring 1. Genes on chromosomes control the traits that show up in an organism 2. The different forms of a trait that a gene may have are alleles.

3. During meiosis a pair of chromosomes separates and the alleles move into separate sex cells. 4. Each sex cell now contains one allele for each trait.

5. The study of how traits are inherited is genetics.

B. Gregor Mendel – the father of genetics 1. Mendel was the first to use mathematics of probability to explain heredity and to trace one trait for several generations.

2. Hybrid – receives different genetic information for a trait from each parent a. Dominant allele – covers up or dominates the other trait. b. Recessive allele – the trait seems to disappear.

3. Probability helps you predict the chance that something will happen. 4. A Punnett square can help you predict what an offspring will look like. a. Upper case letters stand for dominant alleles. ( Y ) b. Lowercase letters stand for recessive alleles. ( y )

5. Genotype – the genetic makeup of an organism a. homozygous – an organism with two alleles for one trait that are the same (written YY or yy) b. heterozygous – an organism with two alleles for one trait that are different (written Yy)

6. Phenotype – the way an organism looks and behaves as a result of its genotype

Discussion Question How do heredity and genetics explain why people are different?

Discussion Question How do heredity and genetics explain why people are different?  People are hybrids. We receive different genetic information from each of our parents.  Our parents carry different alleles for the same trait. Example: Alleles = genes Trait eye color  These alleles can combine in different ways to create different traits in people.

Section 2 – Genetics Since Mendel Learning Objectives 1. Explain how traits are inherited by incomplete dominance. 2. Compare multiple alleles and polygenic inheritance, and give examples of each. 3. Describe two human genetic disorders and how they are inherited. 4. Explain how sex-linked traits are passed to offspring.

Section 2 – Genetics Since Mendel A. Incomplete dominance 1. Neither allele for a trait is dominant. 2. The phenotype produced is intermediate between the two homozygous parents.

B. Multiple Alleles 1. More than two alleles that control a trait are called multiple alleles. 2. Traits controlled by multiple alleles produce more than three phenotypes.

C. Polygenic inheritance 1. A group of gene pairs acts together to produce a trait, which creates more variety in phenotypes (Looks + behavior) 2. Many human traits are controlled by polygenic inheritance, such as hair and eye color.

D. Mutations – genes that are altered or copied incorrectly 1. A mutation can be harmful, beneficial, or have no effect 2. Chromosome disorders – caused by more or fewer chromosomes than normal 3. Down’s syndrome – caused by an extra copy of chromosome 21

Down Syndrome

E. Recessive genetic disorders 1. Both parents have a recessive allele responsible for the disorder and pass it to their child. 2. Because the parents are heterozygous, they don’t show any symptoms. 3. Cystic fibrosis is a homozygous recessive disorder

F. Sex Determination (Male or Female?) 1. Chromosomes that determine the sex of an organism are XX in females and XY in males. 2. Females produce eggs with an X chromosome only. Males produce sperm with either an X or a Y chromosome.

G. Sex-linked disorders 1. An allele inherited on an X or Y chromosome is a sex-linked gene. 2. Color blindness is a sex-linked disorder caused by a recessive allele on the X chromosome. 3. A pedigree follows a trait through generations of a family.

Discussion Question How does your environment affect your hereditary traits?

Discussion Question How does your environment affect your hereditary traits?  Although genes determine many of your traits, you may be able to influence their expression by the decisions you make.  For example, you may have genes that put you at risk for developing skin cancer, but if you limit your exposure to the sun, you may never develop skin cancer.

Section 3 – Advances in Genetics Learning Objectives 1. Evaluate the importance of advances in genetics. 2. Sequence the steps in making genetically engineered organisms.

Section 3 – Advance in Genetics A. Genetic engineering – changing the arrangement of DNA that makes up a gene 1. Recombinant DNA a. Insertion of a useful segment of DNA into a bacterium b. Insulin is made by genetically engineered organisms.

2. Gene therapy a. A normal allele is placed into a virus, which delivers the normal allele when it infects its target cell. b. May be used to control cystic fibrosis or other genetic disorders.

B. Genetically engineered plants – created by inserting the genes that produce desired traits in one plant into a different plant. GMOs (Genetically Modified Organisms) – genes are changed for desired traits Example: Corn that is resistant to drought or even resistant to the weed killer: Roundup

Discussion Question Explain how gene therapy could control cystic fibrosis and other genetic disorders.

Discussion Question Explain how gene therapy could control cystic fibrosis and other genetic disorders.  People with cystic fibrosis have received faulty genetic information form their parents.  Their genes tell their bodies to create thick mucus rather than thin fluid to lubricate the lungs.  Gene therapy can be used to infect their cells with viruses carrying normal alleles with correct genetic information.