Mendelian Genetics Section 6.3, 6.4. and 6.5

6.3 Mendel and Heredity

 What are traits? Traits are distinguishing characteristics such as eye color, leaf shape and tail length. Traits are passed down from generation to generation.

 Who is Mendel and what is the study of genetics? Gregor Mendel is a an Austrian monk who studied thousands of plants and described how traits were passed from generations. Genetics – is the study of the biological inheritance patterns and variations in organisms.

 What was Mendel’s experiment? Mendel chose pea plants because they reproduce quickly. Pea flower typically self-pollinates and a long line of self-pollinated flowers are called purebred He removed the male parts of the flower and cross-pollinated with sperm from another flower.

 What seven traits did Mendel examine? Pea shape, pea color, pod shape, pod color, plant height, flower color and flower position.

 What is a cross and give an example of one of Mendel’s crosses? A cross is the mating of two organisms. Mendel crossed a purebred white-flowered pea plant with a purebred purple flower pea plant. Parent Generation – P generation First Filial – F1 generation – all were purple flowers and allowed to self-fertilize Second Filial – F2 generation – plants had purple flowers or white flowers.

What is the law of segregation? Organisms inherit two copies of each gene, one from each parent. Organisms donate only one copy of each gene in their gametes. The two copies of each gene segregate, or separate, during gamete formation.

6.4 Traits, Genes and Alleles

 What is the difference between a gene and an allele? A gene is a piece of DNA that provides a set of instructions to a cell to make a certain protein. An allele is any of the alternative forms of a gene that occur at a specific locus. Your cells have two alleles for each gene. Alleles are often represented by a capital or lowercase letter.

 What is the difference between homozygous and heterozygous? Homozygous describes two of the alleles at a specific locus. Both code for purple flowers. Heterozygous describes two different alleles at a specific locus. One might code for purple flowers while the other codes for white flowers.

 What is a genome? A genome is all of an organism’s genetic material. Your unique genome determines all of your traits.

 What is the difference between phenotype and genotype? A genotype typically refers to the genetic makeup of a specific set of genes. The phenotype is the physical appearance of an individual organism such as blue eyes, or blond hair.

 What is the difference between dominant and recessive alleles? A dominant allele is the allele that is expressed when two different alleles or two dominant alleles are present. A recessive allele is the allele that is only expressed when two copies are present.

 How are alleles important in determining the phenotype? Two genotypes can produce the same dominant phenotype. Homozygous dominant (TT) or a heterozygous dominant (Tt) could produce a tall plant. A homozygous recessive (tt) is the only one that produces a small plant.