Principles of Heredity Genetics Principles of Heredity

Mendel’s Work Gregor Mendel- known as the “Father of Genetics” Studied Pea plants in a Monastery’s Garden Mendel observed that the pea plants’ traits were often similar to those of their parents. However, sometimes the pea plants had different traits than their parents. The passing of traits (different physical characteristics) from parents to offspring is called Heredity. Mendel spent 10 years experimenting with thousands of pea plants. Mendel’s work formed the foundation of genetics, the scientific study of heredity.

Language Arts Connection Gregor Mendel presented a detailed description of his observations in a scientific paper in 1866. In the excerpt that follows, notice how clearly he describes his observations of the two different seed shapes. “These are either round or roundish, the depressions, if any, occur on the surface, being always only shallow; or they are irregularly angular and deeply wrinkled.” Choose an everyday object, such as a piece of fruit or a pen. Make a list of the object’s features. Then write a short paragraph describing the object. Use clear, precise language in your description.

Dominant and Recessive Alleles Allele-different forms of a gene. Dominant Alleles- is one whose trait always shows up in the organism when the allele is present. Recessive Alleles- is masked, or covered up, whenever the dominant allele is present.

Mendel’s Experiments Life’s Structure & Function Page 129 Writing to Learn- Imagine that you are a student in the 1860’s visiting Gregor Mendel in his Garden. Write a letter to a friend describing Mendel’s experiments with pea plants.

Principles of Heredity Genetics Principles of Heredity

Inheritance of Traits Phenotype- The appearance of an organism. Genotype- the genetic make-up of an organism, or the traits that it carries. Dominant alleles (genes) represented by = capital letters (T) Recessive alleles (genes) represented by = lower case (t)

Punnett Squares T t T T T T t t t t T t A punnett square is a table that shows all the possible combinations of traits among the offspring produced in a cross. T t Genotype of Parents T T T T t t t t T t

Problems Life’s Structure & Function: p133 Practice Problems: 1-2 Self-Check: p. 134 1-5

Phenotypes & Genotypes Homozygous- is an organism that has two identical alleles for a trait. Heterozygous- is an organism that has two different alleles for a trait. Phenotype Genotype Tall TT Tt Short tt Homozygous Heterozygous Homozygous

In codominance, the alleles are neither dominant nor recessive. In incomplete Dominance, no alleles are completely dominant.

Chromosomes Nucleus DNA

Activity Read pages 136-142. Self-Check p. 142 (1-5)

Genetic Disorders A genetic disorder is an abnormal condition that a person inherits through genes or chromosomes. Genetic disorders are caused by mutations, or changes in a person’s DNA. Cystic Fibrosis- a genetic disorder in which the body produces abnormally thick mucus in the lungs and intestine. -hard to breathe -caused by a mutation

Genetic Disorders Sickle-cell disease- a genetic disease that affects the blood. -suffer from lack of oxygen in the blood and experience pain and weakness. Hemophilia- is a genetic disorder in which a person’s blood clots very slowly or not at all. -a person with this disease can bleed to death.

Writing to Learn As the webmaster for a national genetics foundation, you must create a web site to inform the public about genetic disorders. Choose one human genetic disorder discussed in this chapter. Write a description of the disorder that you will use for the Website.

Problem Solving Suppose you are growing purebred green-skinned watermelons. One day you find a mutant striped watermelon. You cross the striped watermelon with a purebred green watermelon. Fifty percent of the offspring are striped, while fifty percent are solid green. Is the allele for the striped trait dominant or recessive? Explain your answer. In Rabbits, the allele for a spotted coat is dominant over the allele for a solid-colored coat. A spotted rabbit was crossed with a solid-colored rabbit. The offspring all had spotted coats. What were the genotypes of the parents? Explain