Chapter 4 Genetics 4.1 Mendel’s Work

POINT > Describe who Gregor Mendel was POINT > Define heredity, trait, and genetics POINT > Explain why pea plants were so useful POINT > Describe Mendel’s experiments POINT > Define genes and alleles POINT > Define dominant and recessive

POINT > Describe who Gregor Mendel was Gregor Mendel (1822-1884) was an Austrian monk and botanist He discovered rules that control how characteristics get passed from parents to offspring He did his work using pea plants in his garden He is known as “The Father of Genetics”

POINT > Define trait, heredity and genetics A trait is a physical characteristic (hair color, eye color, height, leaf size, etc) Heredity is the passing of traits from parents to offspring Genetics is the study of heredity

CHECK: What kind of plant did Mendel use? What is genetics? What is heredity? What is a trait?

POINT > Explain why pea plants were so useful 1) Mendel noticed that some pea plants have different traits

POINT > Explain why pea plants were so useful 2) Mendel noticed that the offspring always had the same traits as the parent plant

POINT > Explain why pea plants were so useful The offspring pea plants always had the same traits as the parent plant = purebred 3) Pea plants are self-pollinating: the plant fertilizes itself

POINT > Explain why pea plants were so useful 4) Pea plant traits are dichotomous: traits were one way or the other, not in between

CHECK: What does dichotomous mean? Pea plants are self-pollinating. What does that mean? What does purebred mean? What are the 3 parts of a nucleotide? What part of the cell cycle includes DNA replication? What are the 3 parts of the cell cycle? What are the 4 phases of mitosis?

POINT > Describe Mendel’s experiments Mendel decided to cross-breed: fertilize plants that had different traits For example, cross a purple flower plant with a white flower plant

POINT > Describe Mendel’s experiments When Mendel did this cross, purple x white, all of the offspring had purple flowers The same result occurred with other traits

POINT > Describe Mendel’s experiments Purple x White = P generation (P=parent) The offspring (all purple) = F1 generation (F=filial)

POINT > Describe Mendel’s experiments Mendel decided to let the F1 generation self-pollinate (F1 x F1) Remember, all these plants had purple flowers

POINT > Describe Mendel’s experiments 25% of the F2 generation were white! The same was true of the other traits 75% -25%

POINT > Describe Mendel’s experiments In the F1 generation 100% showed one trait In the F2 generation there was always a 3:1 ratio

POINT > Describe Mendel’s experiments This was a mystery, but Mendel solved it He found that the factors that control traits come in pairs (2 factors for each trait) One of the factors comes from each parent One of the factors can cover up the other one

POINT > Define genes and alleles The factors that control traits come in pairs (2) We now call these factors genes. Genes control what traits appear in an individual Different forms of a gene for one trait are called alleles For example, there is an allele for purple flowers and an allele for white flowers

CHECK: What do genes do? What are alleles? What is a prokaryote?

POINT > Define genes and alleles For example, there is an allele for purple flowers and an allele for white flowers Ex. One allele for tall plants and one allele for short plants When two different alleles are in one plant, one of the alleles is dominant over the other allele

POINT > Define dominant and recessive One allele is dominant and the other allele is recessive Ex. The allele for purple flowers is dominant and the allele for white flowers is recessive A plant with one purple allele and one white allele will have all purple flowers

POINT > Define dominant and recessive We identify the dominant allele with capital letters: ex. P for purple flowers We identify the recessive allele by using small letters: ex. p for white flowers T = tall plant allele t = short plant allele

POINT > Define dominant and recessive Each individual has two alleles for a trait PP - plant has two dominant alleles (purple flowers) pp - plant has two recessive alleles (white flowers) Pp - plant has one dominant and one recessive allele (purple flowers)

CHECK: How many alleles are there for one trait? Which is the dominant allele: “R” or “r”? P is the dominant allele and gives purple flowers. p is the recessive allele and gives white flowers. If a plant has one P allele and one p allele, what color are the flowers? What are the alleles of a plant with white flowers?

Homework: Complete Study Guide Read pages 110-115 S.A. page 115 #1-2 GRAS pages 55-57