Download 3) Section 2 - Note Taking

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Chapter 20 – The Role of Genes in Inheritance
Section 2 – Genetics – The Study of Inheritance
A. Heredity - passing traits from parents to offspring.
B. Genetics - is the study of how traits are passed from parents to offspring.
C. A gene is a small section of DNA on a chromosome that has information about traits.
1. Thousands of genes are arranged on 23 pairs of chromosomes.
2. Humans should have a total of 46 chromosomes.
D. What determines traits?
1. Each gene of a gene pair is called an allele.
2. When a pair of chromosomes contains different alleles for a trait, the trait is called hybrid.
3. When a trait has two identical alleles, the trait is called pure.
E. Dominant and Recessive Alleles
1. A dominant allele will mask the other allele for a particular trait.
2. Recessive alleles show when two copies of the recessive allele are inherited.
3. To show a dominant allele a person can have 1 or 2 alleles for the trait.
D. Expression of Traits
1. The environment can play an important role in the way a trait is shown.
2. Variations are the different ways that a certain trait appears.
*examples are different hair color, eye color, and skin color.
3. A mutation is a change in a gene or chromosome.
*mutations can be helpful, harmful, or neutral.
4. Selective breeding results in organisms with desired traits.