Heredity

1. Heredity Chapter 5 Life Science

2. Section 1 Mendel and his peas • Characteristics of humans are determined by a complicated process of parents sending information to their offspring. • Heredityis the passing of genetic traits from parents to offspring. • Gregor Mendel is given credit for discovering the principles of heredity while studying pea plants. • His discoveries took place while serving as a monk in a monetary. He has been given the title of “Father of Genetics”. • From working with plants, Mendel knew that the patterns of inheritance were not always clear. • Some traits seem to disappear for a generation and then reappear. To determine how this happens, Medal concentrated on one type of plant, the pea plant. • Pea plants were a good choice because they grow quickly and self-pollinate.

3. Section 1 • Self pollinating plants have both male and female reproductive structures. • The pollen of one plant can fertilize the ovule of the same plant or another plant. • If the offspring have all the same traits as the parent, they are called truebreeding plants. • In cross-pollination, pollen can be carried by wind, water, or insects to the second plant. • Mendel studied one characteristic at a time. He called these characteristics traits. • Mendel used true-breeding plants to study each trait and controlled whether they self-pollinated and cross-pollinated. • In Mendel’s experiment, one trait would always seem to show up. He called this the dominate trait. The trait that seemed to disappear, he called a recessive trait. • The recessive trait reappeared in the second offspring. • Mendel decided to determine the ratio that each trait shows up.

4. Section 2heredity • Scientists now call these instructions for inherited trait genes. Each parent gives one set of genes to the offspring. • The offspring has two genes, called alleles, for each characteristic. • Dominant alleles are represented by capital letters while recessive alleles are represented by lowercase letters. • An organism's appearance is known as phenotype. The inherited information (alleles) is called the genotype. • An organism with two dominant or recessive alleles is homozygous while an organism with one dominant and one recessive allele is heterozygous. • A Punnett square is used to organize all the possible combinations of offspring from particular parents. • The mathematical chance something will occur is called probability. • Exceptions can occur with Mendel’s findings. Incomplete dominance is when one trait cannot cover another. • Other exceptions include one trait controlling many traits, many genes controlling one trait, or the environment can be a factor in traits adapting to conditions.

5. Section 3 meiosis • Mitosis is the asexual reproduction of cells where chromosomes are copied and the cells divides once resulting in a new cell with the same # of chromosomes as the parent. • Meiosis is the reproduction of sex cells where the cell divides twice after the chromosomes are copied. The new cell has ½ the # of chromosomes as the parent. • Meiosis occurs in the sperm and egg cells of animals and humans. • Sex chromosomes determine if an offspring is male or female. If the pair is XX, the offspring is female. If the pair is XY, the offspring is male. • There are some sex linked traits and disorders. Common disorders are color blindness and hemophilia. • A pedigree is a diagram that shows the occurrence of a genetic trait in several generations of a family. • In the process of selective breeding, organisms with desirable traits are mated.

6. Punnett Square practice • In pea plants, yellow seeds are dominant to green seeds. Find all possible genotypes and phenotypes of across between a heterozygous yellow seed plant and a green seed plant. • In rabbits, black fur is dominant to grey fur. Cross two heterozygous black rabbits and find the genotypes and phenotypes.

7. Daily assignment • Page 133 # 2-6, 8-10 answers only • Pages 136 and 137 # 1-15, 17 – 23 answers only