Chapter 3: Genetics Section 1: What is Heredity? The passing of traits from parents to offspring Genetics – the scientific study of heredity “Father of Genetics” - Gregor Mendel

Why did Mendel study Peas? Pea plants have many traits that exist in only two forms Garden peas produce a large number of offspring in one generation

How did Mendel’s experiments work? Mendel crossed plants with opposite forms of a trait, for example, tall plants and short plants Purebred – An organism that always produces offspring with the same form of a trait as the parent

What other traits did Mendel study? Stem Height Seed shape Seed color Seed coat color Pod shape Pod color Flower position

What are genes and alleles? Genes – A segment of DNA on a chromosome that codes for a specific trait Alleles – the different forms of a gene Each offspring inherits two alleles – one from each parent

What are the types of alleles? Dominant – An allele whose trait always shows up in the organism when the allele is present (ex. TT Tt) Recessive – An allele that is masked when a dominant allele is present (tt)

What is a Hybrid? An organism that has two different alleles for a trait; an organism that is heterozygous for a particular trait (Tt)

How are alleles represented in shorthand? Geneticists use letters Dominant allele = capital letter (T) Recessive allele = lowercase letter (t)

Section 2: Probability and Genetics What is Probability? The likelihood that a particular event will occur What is likely to occur; not necessarily what will occur More trials brings you closer to the actual results

How is probability related to genetics? Mendel discovered that the mathematical principles of probability applied to his work The principles of probability can be used to predict the results of genetic crosses Example: Probability of producing a tall plant 3 in 4 Probability of producing a small plant 1 in 4

What is a Punnett Square? A chart that shows all the possible combinations of alleles that can result from a genetic cross They show all the possible outcomes of a genetic cross and determine the probability of a particular outcome

How do you read a punnett square to determine genetic probability? When Mendel performed his cross he discovered that 75% of the plants had tall stems (3 out of the 4 plants) and 25 % of the plants had short stems ( 1 of the 4 plants)

What are two of the terms geneticists use to describe organisms? Phenotype – an organism’s physical appearance, or visible traits (Ex. Stem height phenotype, tall or short) Genotype – An organism’s genetic makeup, or allele combinations

What are two additional terms geneticists use to describe an organism? Homozygous – Having two identical alleles for a trait (Ex: TT, tt) Heterozygous – Having two different alleles for a trait (Ex: Tt)

What term did Mendel use to describe heterozygous pea plants? Hybrid

Found in Erminette chickens and cattle What is Codominance? A condition in which neither of two alleles of a gene is dominant or recessive Found in Erminette chickens and cattle

Genes are carried from parents to their offspring on chromosomes Section 3: The Cell and Inheritance Who is Walter Sutton and what did he discover? Walter Sutton was an American geneticist whose idea came to be known as the chromosome theory of inheritance Genes are carried from parents to their offspring on chromosomes

What is Meiosis? The process that occurs in sex cells (sperm and egg) by which the number of chromosomes is reduced by half There are 46 total chromosomes in your body; 23 pairs; 23 came from your dad and 23 came from your mom

The same is true for the egg cells from the female parent How can Punnett Squares be used to show how alleles separate when sex cells form during Meoisis? Half of the sperm cells from the male parent will receive the chromosomes with the P allele; the other half receive the p allele The same is true for the egg cells from the female parent

If you unwrap all the DNA in your cells you could reach the moon!!! If we only have 23 pairs of chromosomes how do we exhibit so many different traits? Each body cell contains more than 60,000 genes and each of those genes controls a particular trait If you unwrap all the DNA in your cells you could reach the moon!!!

Section 4: The DNA Connection What is the Genetic Code? Cells are made up of chromosomes; chromosomes are made up of DNA; DNA is made up of nitrogen bases The order of nitrogen bases along a gene forms a genetic code that specifies what type of protein will be produced A group of three bases codes for the attachment of a specific amino acid Cell Chromosome DNA Nitrogen bases

What are amino acids? The building blocks of proteins The order of the bases determines the order in which amino acids are put together to form a protein - like a three-letter code

How do cells make Proteins? Protein Synthesis – the cell uses information from a gene on a chromosome to produce a specific protein Takes place on the ribosomes in the cytoplasm

What must happen before protein synthesis can take place? A “messenger” must first carry the genetic code from the DNA inside the nucleus to the cytoplasm – called RNA

How is RNA different from DNA? DNA looks like a twisted ladder while RNA almost always looks like only one strand, or side, of the ladder Instead of Thymine RNA contains Uracil RNA

What are the types of RNA? Messenger RNA – copies the coded message from the DNA in the nucleus Transfer RNA – carries amino acids and adds them to growing proteins

What is the process of protein synthesis? A DNA molecule “unzips” between its base pairs allowing the RNA bases to pair up with the DNA bases – Adenine with Uracil Messenger RNA leaves the nucleus and enters the cytoplasm, where it attaches it a ribosome and production of the protein chain begins (3 letter code) Transfer RNA attaches to messenger RNA putting the amino acids it is carrying in the correct order Protein production is complete when the ribosome reaches a three-letter code that acts as a stop sign – completed protein chain is released

How do Mutations affect DNA? Mutations can cause a cell to produce an incorrect protein during protein synthesis Some of the changes brought about by mutations are harmful to an organism; however, some are helpful or neither harmful or helpful