GENETICS

 What is DNA?  Hereditary material that contains information for an organism’s growth and function  Chemical code—like an alphabet  Stands for Deoxyribonucleic acid  DNA is stored in the  It is copied during cell division and passed to new cells nucleus

 1952s—Rosalind Franklin discovered DNA’s structure using X-ray  1953—Watson and Crick made a model of DNA  They said DNA looked like a double helix or a twisted ladder

 Each side of the ladder is made up of two parts  Deoxyribose—a sugar  Phosphate D P D P D P D P D P D P  The sugar and phosphate alternate forming the backbone of the model.

 The steps of the ladder are made of nitrogen bases  The bases pair together with two at each step D P D P D P D P D P D P A A T T G C  Four bases—always pair following this pattern AdenineThymine GuanineCytosine

 When chromosomes are copied in mitosis & meiosis, DNA is doubled too  The sides of the DNA unwind (like a zipper)  New bases are added to each old strand  A—T  C—G

 Which cell structure makes proteins?  Proteins are made up of chains of amino acids  Most of your characteristics, eye color, height, how things taste to you, depend on the proteins made by your cells  DNA has the instructions for making these proteins ribosomes

 Each chromosome contains hundreds of genes  The instructions for a certain protein are found on genes  Genes are sections of DNA on chromosomes that contain certain instructions for building proteins  The gene determines the order of amino acids in a protein  Changing the order of the amino acids makes a different protein

 Genes are found in the nucleus, but proteins are made on ribosomes in the cytoplasm  How does the ribosome make the protein if the DNA is in the nucleus?  RNA (ribonucleic acid)  carries the code from the nucleus to the ribosome  only has one strand  has the same bases, except it has Uracil (U) instead of thymine  made in the nucleus from a DNA pattern A A G T

 Three kinds of RNA  mRNA: messenger RNA  moves to cytoplasm and ribosomes attach to it  rRNA: ribosomal RNA  makes up ribosomes  tRNA: transfer RNA  brings amino acids to the ribosomes

 Inside the ribosome  3 mRNA bases pair with 3 tRNA bases  the tRNA has an amino acid attached to it (brought from rRNA)  Each amino acid bonds together, forming a protein

Controlling Genes  Not every cell makes the same proteins  Each cell uses only the genes that direct the making of proteins that it needs  Example: Muscle cells use genes that make muscle proteins—Nerve cells don’t need those muscle proteins so they don’t make them  Cells have the ability to turn on or turn off genes

 What happens if the DNA is not copied correctly?  Causes mistakes or mutations  Permanent changes in DNA  X-rays, sunlight, and some chemicals can cause mutations  Can be good or bad depending on how it affects the organism

5-1: Mendel’s Genetics  All of your characteristics or features (eye color, hair color, nose shape) is inherited from your parents  An organism is a collection of these features which are called traits  Heredity is the passing of traits from parents to offspring.

 Remember, genes on chromosomes control traits or characteristics of organisms.  There can be different forms of those traits on the same gene.  Those different forms of traits are called alleles. Alleles for this trait are A and a. Organisms with the same alleles are homozygous. Organisms with different alleles are heterozygous. Aa

 When chromosomes separate during meiosis, one allele goes into each sex cell.  Sex cells contain only 1 allele for each trait.  The new offspring will now have 2 alleles.

 Genetics is the study of how traits are inherited.  Gregor Mendel—“The Father of Genetics”  responsible for starting the science of genetics  worked with pea plants and studied their traits

 He found that tall plants crossed with short plants produced all tall plants.  Tall form is dominant because it dominates or covers up the short form.  Short form is recessive because it seems to disappear.

 By studying his pea plants so closely, Mendel could predict what the offspring would look like based on which parent plants he crossed.  He did so using a Punnett Square Letters represent dominant and recessive alleles. Always represent dominant alleles using capital letters. Always represent recessive alleles using lowercase letters. Y y

 Punnett squares show us  Genotype: genetic make-up for the trait (alleles)  Phenotype: physical appearance for trait (what they look like); results from genotype Cross for Seed Color Y = yellow y = green YY = Yy = yy = yellow green Genotype Phenotype

Tongue-rolling is dominant to non-tongue rolling. A father who is homozygous for tongue-rolling and a mother who is homozygous for non- tongue rolling have a baby. What is the probability that the baby will be able to roll their tongue?

5-2: Genetics Since Mendel  Not every trait follows the simple dominant/recessive pattern that Mendel studied  There are several different ways that traits can be expressed

Incomplete Dominance  Sometimes the heterozygous offspring will look like a mixture of the homozygous parents  This is called incomplete dominance  Some flowers and horse colors are this way

Multiple Alleles  Some traits are controlled by more than 2 alleles  They are said to have multiple alleles and produce more than 2 phenotypes  Human blood types are multiple alleles  The alleles for human blood are A, B, and i  These three alleles can produce type A, type B, type AB, or type O blood in humans

Polygenic Inheritance  Traits controlled by more than 1 gene are said to be polygenic  Examples include eye color, skin color, and height  Environmental factors also influence polygenic expression

Chromosome Disorders  Mistakes during meiosis can cause the offspring to have more or less than the normal number of chromosomes  Example: Down’s Syndrome  occurs when an extra #21 chromosome is put into a sex cell (chromosomes don’t separate correctly)

Genetic Disorders  Most inherited disorders are recessive, meaning you have to have 2 alleles (rr) for it to show up  Examples include:  Cystic fibrosis  Tay-sachs  PKU

Sex Determination  Female eggs will contain one X chromosome  Male sperm will contain either one X or one Y chromosome  Babies can either be female (XX) or male (XY) Y XX Female Y XY Male

Sex-Linked Traits  Alleles on sex chromosomes (X or Y) are sex- linked traits  Examples  Color-blindness  Hairy Ears

Pedigrees  A visual tool for following a trait through generations of a family

5-3: Advances in Genetics  Scientists have been able to change DNA sequences to help people with disorders  Genetic engineering is the science of changing the arrangement of DNA  Has been used to make medicines

 Recombinant DNA  Putting a “good” piece of DNA into a bacteria  The bacteria will then make more of that DNA piece  Used to make insulin, growth hormone, and other chemicals

 Gene Therapy  put a normal allele into a virus and then insert the virus into a person with the disorder  the virus then replaces the bad allele with the good one  using this with cystic fibrosis and cancer

 Genetically Engineered Plants  produces better crops  bigger plants  better-tasting plants