Heredity Basic Notes PP. 126-132

Heredity Basics Notes: Heredity is the passing of traits from parent to offspring. The study of how these traits are inherited is genetics.

What is genetics? 2. Genes are found on chromosomes and control the traits that show up in an organism. The different forms a gene may have for a trait is an allele. During MEOSIS, a pair of chromosomes separate and the alleles move into separate gametes. Each gamete now contains 1 allele for each trait.

Mendel – The Father of Genetics 3. Mendel was the first to use mathematics of probability to explain heredity and to trace one trait for several generations.

Hybrid & Purebred 4. Hybrid organisms receive different genetic information for a trait from each parent. 5. An organism that always produces the same traits generation after generation is called a purebred. PUREBRED organisms receive the same or identical genetic information for a trait from each parent.

Dominant and Recessive 6. The dominant allele covers up or dominates the other allele (use capital letters to represent trait). 7. The recessive allele seems to be covered up or “disappears” (use lower case letter to represent trait).

Probability Punnett Squares 8. Probability helps one predict the chance that something will happen. Punnett Squares 9. A Punnett square can help predict what an offspring will look like. 10. Upper case letters stand for dominant alleles. Lower case letters stand for recessive alleles.

Genotype & Phenotype 11. The genotype is the genetic makeup of an organism (examples: RR, TT, Tt, Rr, Ll, LL). The phenotype is the way an organism looks or behaves as a result of the genotype (examples: brown hair, blue eyes, tall, short). The PHENOTYPE is the EXPRESSION of the GENOTYPE!

Homozygous & Heterozygous 12. An organism with two alleles that are the same is said to be homozygous. Would this organism be hybrid or purebred for the trait? PUREBRED An organism with 2 alleles for one trait that are different is said to be heterozygous. Would this organism be purebred or hybrid for this trait? HYBRID

Math Skills Activity p. 131 This is Punnett Square: It is a simple way to calculate the PROBABILITY of a genetic cross.

Practice Problem: 1. In peas, the color yellow (Y) is dominant to the color green (y). According to the Punnett square, what is the probability of an offspring being yellow? 2. What is the probability of an offspring having the yy genotype?

Table 2 Principle of Heredity 1 Traits are controlled by alleles on chromosomes. 2 An alleles effect is dominant or recessive 3 When a pair of chromosomes separates during meiosis, the different alleles for a trait move into separate sex cells (gametes).

Genes are located on chromosomes Genes are located on chromosomes. The chromosomes in a pair may have different alleles for some genes and the same alleles for others. For which gene is this organism heterozygous? Aa Homozygous? BB A B a B