Introduction to Genetics Chapter 11

Introduction We have already learned about meiosis… Why is meiosis important?

Genetics: The scientific study of heredity The study of how gametes (from meiosis) combine and which traits are expressed!

History Gregor Mendel- Austrian monk, teacher, and gardener Studied heredity of pea plants –Which traits (color, texture, etc.) were expressed under different conditions and breeding situations Drew two conclusions from his experiments

Conclusion 1 Biological inheritance is determined by factors that are passed down from one generation to the next. –These “factors” are called genes. –Every trait is controlled by one or more genes. Different forms of genes are called alleles. Example: eye color=trait blue, brown, green, hazel=alleles Segregation is the separation of alleles during gamete formation---during meiosis!!

Conclusion 2 Some alleles are dominant, some are recessive. –If an organism has a dominant allele for a trait, that is the allele that will be expressed. –Example: Yellow peas are dominant over green peas. If the yellow pea allele is present even once, the peas will be yellow.

How did Mendel do it? Fertilization is the meeting of the gametes (in sexual reproduction). True-breeding plants self-pollinate to produce exact copies of themselves (clones). Cross-pollination occurs when gametes from two different individuals are combined. –Cross-pollination of individuals with different traits makes a hybrid. Mendel crossed pea plants to determine what traits would be expressed in the offspring.

How Pollination works:

Examples of Segregation: The first diagram shows segregation: each parent’s alleles separate and combine with the alleles of the other parent. The second diagram is a Punnett Square. It is used to show the segregation of alleles and the probability of combinations. What words can we use to describe this cross? Aa x Aa A aA a AA AaAa aa Aa AAAAa a aa

Description: Parents (Aa) are heterozygous: having two different alleles. There is a 50% chance the offspring will also be heterozygous. There is a 25% chance the offspring will be homozygous and recessive. (aa) There is a 25% chance the offspring will have AA, which is homozygous and dominant. (AA) –Homozygous: having two of the same alleles. Aa AAAAa a aa

Phenotype and Genotype Phenotype is a word used to described the physical characteristics expressed by the genes. (Think pheno=physical!) Genotype is a word used to describe the genetic makeup of that characteristic. (Think geno=genes!) –Example 1: “TT” would be the genotype while “tall” would be the phenotype. –Example 2: “Tt” would be the genotype while “tall” would be the phenotype.

Question: If A represents normal color and a represents albino: 1.Which is dominant…normal or albino? 2.What are the phenotypes of both parents? 3.What are the phenotypes of the four possible offspring? Aa AAAAa a aa