Genetics Where do you think the directions for making you came from?"

Inheritance: what makes you- YOU!  Inheritance occurs through sexual reproduction.  During sexual reproduction, a cell that contains genetic information from the mother and father join to form a completely new cell.  Each parent organism contains one-half of the genetic material need to create a new organism.

DNA  Stands for: Deoxyribonucleic acid  It is where genetic information is stored.  It determines every inherited physical characteristics of every living thing.  It controls how the cell replicates and functions.

What is a Gene?  A short unit of DNA that codes for a particular trait, like a recipe.  Genes are responsible for the inherited characteristics that distinguish one individual from another.  Genes for a specific trait come in pairs.  There are approximately 30,000 genes in each cell of the human body.  The combination of all genes make up the blue print for the human body and its functions  A person’s genetic makeup is called a genotype  The physical expression of genes is called phenotype.

Juicy Science Question?  What would happen if something went wrong in the DNA sequence?

Chromosomes  In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes.  Chromosomes come in pairs. Each member in the pair is called a homolog, or sister chromatid.  Genes have a specific location on the chromosome.

What is an Allele?  One gene from the pair of homologs is called an Allele.  An alternate form of a specific gene.  For example, one homolog of a chromosome may have an allele for Regular height (A) and the other homolog May have an allele for short height (a).  The alleles on a pair of homologs may or may not be different.

Chromosome Number  Each species has a characteristic number o chromosomes.  Chimpanzees: 24 chromosome pairs  Fruit flies have 4 chromosome pairs  Humans have 23 chromosome pairs

 Heredity is the passing of traits from one generation to another.  Heredity determines certain specific characteristics of plants and animals.  Animals can inherit behavioral, mental, and physical traits. Another word for heredity is inheritance.

Inherited Traits  Characteristics that are passed from parent to offspring.  For example:  Eye color  Eye shape  Hair type  Face shape  Some traits are dominant and some are recessive.

Dominant Traits  A trait that will always be expressed in the phenotype.  These are represented by CAPITAL letters. For example, A.

Content Check  What is the difference between phenotype and genotype?  Phenotype= physical characteristic displayed. Ex, eye color  Genotype= Set of genes carried by an organism

Recessive Trait  A trait that will only be expressed in the phenotype if two recessive alleles are present.  Represented by lowercase letters.  For example, a.  The genotype aa would express the recessive trait.  IN THE PRESENCE OF A DOMINANT TRAIT, THE RECESSIVE TRAIT WILL NOT BE EXPRESSED.

Sex Linked Traits  Males have an XY chromosome combination  Females have an XX chromosome combination  Genes that are carried by either sex chromosome are said to be sex linked  X-linked diseases usually occur in males. Males have only one X chromosome. A single recessive gene on that X chromosome will cause the disease.

 Austrian Monk & the “father” of genetics  Before he became a Monk, he attended university to study science and Math.  He studied pea plants to prove the existence of genes.  He hypothesized that genes Controlled several different traits : Height, seed shape, seed color, and flower color are a few examples.

Punnett Squares  Mendel observed seven traits in pea plants.  Mendal realized that each plant must have “two factors” for each possible trait, one factor from each parent.  Some traits like dwarf height could be masked. (recessive)  A Punnett square helps diagram the probability of each possibility genotype and phenotype in a generation.  Mendel described the pea plant factors as alleles

Punnett Squares  In a Punnett square, the top of the table shows the alleles provided by one parent.  The alleles for the other parent are placed along the left side of the table.  One allele from each parent is placed in the individual squares, forming a new gene pair.  The individual squares show the possibilities of allele pairs in the offspring.

Punnett Square Example The cross Tt x tt: tt T t Tt tt

 As the Punnett square shows, TT, Tt, and tt are all possible genotypes for the height of the offspring.  The offspring with the genotypes TT and Tt will have a phenotype of tall; the offspring with the genotype of tt will have a phenotype of short.  If the two alleles are the same (TT or tt), the genotype is considered purebred. If the two alleles are different (Tt), the genotype is considered hybrid.  This example shows the inheritance of a single characteristic (height). A cross that shows the inheritance of a single characteristic is known as a monohybrid cross.  It is sometimes difficult to predict certain traits in humans (for example hair color or eye color) because there may be several different genes that control these traits.