Genetics Introduction! Heredity and Variation

Objective I will be able to explain how chromosomes separate randomly to create genetic variation.

Review 1. What gets separated during meiosis I? A. spindle fibers B. mitochondria C. sister chromatids D. homologous chromosomes 2. Which of these correctly describes a chromosome? A. proteins that form enzymes B. contains genes that code for traits C. phospholipids that make up cell membranes D. molecules that create the nucleus

What is genetics? The study of: heredity patterns variation

What exactly is heredity? Heredity: Passing of traits from parents or ancestors to offspring. Example: Type 1 Diabetes may be passed from your parents to you.

What is a trait? Trait: A characteristic that is inherited from parents What is a trait you’ve inherited from your parents or ancestors?

Genetic Variation Variation: Differences in physical traits of an individual from the group to which it belongs Even though traits are passed on from the parents, each new generation shows variation

Human Variation in Skin Color

What are the ways variation is produced? …It’s all about meiosis and sex!

1. Law of Segregation Note: segregation = separation The homologous chromosomes get separated when the gametes are formed. Each gamete only gets one copy of the chromosome pair, so the next generation has a 50-50 chance of inheriting a particular trait

2. Law of Independent Assortment Each pair of chromosomes line up and separate randomly and independently of each other Example: Just because you have brown hair doesn’t mean you’ll inherit brown eyes It all depends on how the chromosomes line up during meiosis!

What are the chances of two gametes having the same chromosomes? The number of chromosome combinations = 2n Humans = 223 That’s about 8 million different gametes per person!

Sperm (8 million) x Egg (8 million) = 3. Random Fertilization Any sperm can fuse with any egg. So what are the chances of siblings having the exact same chromosomes? Sperm (8 million) x Egg (8 million) = 1 in 70 trillion!

And if that’s not enough variation there’s also CROSSING OVER! During meiosis I chromosomes may “trade” a section of DNA This is a normal process that further increases variation in the offspring.

Review Question #1 The puppies pictured are all brothers and sisters. What is the primary cause of the variation seen in these offspring? A. Independent assortment of chromosomes B. Cytoplasmic division during cytokinesis C. Environmental changes D. Mutation Answer: D Learning Goal: LG 4.e: Compare the processes of mitosis and meiosis with respect to their significance to sexual and asexual reproduction, genetic variation, number of cells produced, and number of chromosome in daughter cells. Objective: LO 4.e.iii. Explain the significance of crossing over in generating genetic variation during meiosis. Source: Teacher-created 16

Review Question: #2

Review #3