1. Heredity- review, notes

2. Heredity Notes The passing of traits from parents to offspring is heredity. Every organism is identified by its characteristics or traits.

3. Some traits you can see: eye color, shape of ear, skin color etc. Some traits involve how the body works: color blindness, immunity controllers.

4. You are born with a code that contains directions for how you will look and how your body will work. You inherited this code from your parents. The code is found inside the chromosomes located in the nucleus of the cell. The chromosomes are made of deoxyribo nucleic acid (DNA).

5. DNA holds the code for thousands of traits by its unique shape- a ladder. The sides of the ladder are made of a phosphate group and a deoxyribose sugar group. The rungs of the ladder are made of four nitrogen bases- adenine, thymine, cytosine and guanine.

6. The order in which the bases are arranged ‘spell’ a message for each trait. A GENE is the message for the trait!

7. A chromosome is made up of a string of genes which is composed of DNA. Chromosomes normally appear in pairs- they have the same appearance and length and the same type of genes.

8. Every species has a certain number of chromosomes- humans- 46 (23 pairs), bats- 44 (22 pairs), chickens- 78 (36 pairs), goats- 60 (30 pairs).

9. For organisms that have two parents, genes are inherited from each parent. Humans get 23 chromosomes from the female, 23 chromosomes from the male, to combine to form the offspring with 46 chromosomes..

10. The reproductive cells (the egg and the sperm) then have half the number of chromosomes as the other cells in an organism. The process where reproductive cells are made is called MEIOSIS.

11. When the sperm and egg meet in human reproduction the results are up to chance- with 23 pairs of chromosomes matching up, there are over 1,000,000 different combinations possible. You will never be identical to a brother or sister born at a different time.

12. The study of inheritance is called genetics. An Austrian named Gregor Mendel studied pea plants- he found that pea plants are either tall or short. He experimented with these plants and discovered genetics- a tall plant crossed with a tall plant led to an tall plant, a short plant crossed with a tall plant led to a tall plant-

13. so the pea plant has a dominant gene for tallness. The tall gene will always overpower the short gene. The pea plant has a recessive gene for shortness.

14. The easy way to determine offspring of parents is to use a punnett square.

15. Phenotype- the physical appearance of offspring The phenotypes will be described as the traits themselves (tall or short) Genotype- the gene combinations of offspring The genotypes can be described as… Heterozygous (one of each)- Tt (also called hybrid) Homozygous (same) TT, tt (also called purebred)

16. Not all traits have dominant and recessive forms- some traits just blend together- ex- some flowers- red and white make pink, and human race.

17. Male- Xy chromosomes Females- XX chromosomes

18. Some genes carry sex-linked traits because the genes are on a sex chromosome. The most common example is color blindness- this is carried on the X chromosome- if a boy has an X y then he will be color blind.