*Define heredity.

* Heredity is the passing of traits from parent to offspring.

*What are genes and where are they located?

*Genes are located on chromosomes and control the traits that show up in an organism.

*Define genetics.

*Genetics is the study of how traits are inherited.

*What are alleles?

*Alleles are the different forms of a trait that a gene may have.

*What happens during meiosis?

*During meiosis a pair of chromosomes separates and the alleles move into separate cells.

*How many genes does each chromosome contain for each trait?

*Each chromosome contains one gene for each trait.

*Gregor Mendel
The Father of Genetics

*Describe Mendel’s contribution to genetics.

*Mendel was the first to use mathematics of probability to explain heredity and to trace one trait for several generations.

*What is probability?

*Probability helps you predict the chance that something will happen.

*Define hybrid.

*If an organism is hybrid, it received different genetic information for a trait from each parent.

*Define dominant allele.

*A dominant allele will cover up or dominate the other trait.

*Define recessive allele.

*With a recessive allele, the trait seems to disappear. A recessive trait can only be seen when recessive alleles for the same characteristic are inherited from both parents.

*What is a Punnett square?

*A Punnett square is a diagram used to show all possible combinations of alleles for a given set of parents. It can be used to help you predict what an offspring will look like. Upper case letters are used to show dominant alleles. Recessive alleles are shown using lower case letters.

*Define genotype.

*What is homozygous?

*An organism is homozygous for a trait if it has two alleles for that trait that are the same. It would be written TT or tt.

*What is heterozygous?

*An organism is heterozygous for a trait if it has two alleles for that trait that are different. It would be written Tt.

*Define phenotype.

*The way that an organism looks and behaves as a result of its genotype is called the phenotype.

*Define incomplete dominance.

*In a case of incomplete dominance neither allele for a trait is dominant. The phenotype that is produced is intermediate between the two homozygous parents.

*What are multiple alleles?

*Multiple alleles are more than two alleles. Traits that are controlled by multiple alleles will produce more than three phenotypes. An example of a trait that is controlled by multiple alleles is blood type in humans.

*Define polygenic inheritance.

*Polygenic inheritance occurs when a group of genes act together to produce a trait. This creates more variety in phenotypes. Many human traits such as hair color and eye color are controlled by polygenic inheritance.

*What are mutations?

*Mutations are changes that occur when genes are altered or copied incorrectly. A mutation can be harmful, beneficial, or have no effect.

*What are chromosome disorders?

*Chromosome disorders are caused by having more or fewer chromosomes than normal.

*What causes Down Syndrome?

*Down Syndrome is caused by having an extra copy of chromosome 21.

*Describe and give an example of a recessive genetic disorder.

*Recessive genetic disorders are caused when both parents have a recessive allele responsible for the disorder and both pass it on to their child. Because both parents are heterozygous, they don’t show any symptoms of the disorder. An example of a homozygous recessive genetic disorder is Cystic Fibrosis.

*What are sex-linked disorders and how are they inherited?

*The genes that determine the sex of an organism are XX in females and XY in males. Female only produce eggs with an X chromosome. Males produce sperm with either an X or a Y chromosome. An allele inherited on an X or Y chromosome is a sex-linked gene. Color blindness is a sex-linked disorder caused by a recessive allele on the X chromosome.

*What is a pedigree?

*A pedigree is a visual tool that is used to trace a trait through several generations of a family.

20. traits