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Heredity and Meiosis Gregor Mendel- Austrian monk that studied heredity. He discovered that certain traits could be passed from generation to generation. He studied pea plants to study traits Heredity- the passing of characteristics from parents to offspring Trait- the characteristic that is inherited, can be seen or unseen Genetics- the study of herdity Sex cells are called gametes Both male and female make them When the male and female gametes unite it is called fertilization and a zygote is formed The zygote then undergoes mitosis and develops into the organism Why mitosis? Monohybrid cross Hybrid- a cross between parents that have different forms of a trait Tall and short stems Red and white flowers Monohybrid cross- a cross of only 1 trait Tall and short Each gene has 2 alleles 1 from mom and 1 from dad Dominant allele- the trait that expresses itself Recessive allele- the trait that is not expressed As long as 1 dominant allele is present that trait will show Law of segregation- each organism has 2 alleles per gene and when gametes are made, each gamete gets 1 of the alleles Phenotype- the way an organism looks or behaves Genotype- the genetic make up of an organism Homozygous- this organism contains the same alleles for a trait Both tall alleles Heterozygous- this organism contains different alleles for the same trait 1 tall and 1 short So how does this affect phenotype and genotype? 2 organisms can look the same, but be very different genetically Dihybrid cross- when you cross 2 alleles at one time Height and color Color and shape Law of independent assortment- each trait is inherited independently from each other. Punnett square Made by Reginald Punnett as a way to quickly see the genotypes of a certain cross. You can use the genotypes to see what phenotypes may occur within a certain cross Practice punnett squares Meiosis Meiosis- the division of chromosomes into gametes with half the information as the whole Cells contain thousands of pieces of genetic material called genes on segments of DNA that make up multiple chromosomes. The human body has 46 chromosomes 23 from each parent Diploid cell- has 2 sets of chromosomes Haploid cell- has 1 set of chromosomes gamete Meiosis Meiosis is used to divide the number of genes in half so that only 1 allele is given to the offspring. Has 2 separate steps similar to mitosis Meiosis 1 Interphase- DNA replicates and sister chromatids become attached by a centromere Prophase 1- chromosomes coil and create a tetradpairing of homologues chromosomes. Cross over occurs between non-sister chromatids and genetic information is split Metaphase 1- the tetrads line up and spindle fibers attach Anaphase 1- the tetrads separate but do not split, this makes sure that each new cell will receive only 1 chromosome per pair Telophase 1- 2 new cells are made, each contains 2 copies of a gene Meiosis 2 Prophase 2- spindle fibers form Metaphase 2-spindle fibers attach and they line up across equator of cell Anaphase 2- sister chromatids split and move to opposite ends Telophase 2- new membrane forms and 4 new single chromosomal cells are made Problems with meiosis Nondisjunction- when a homologous pair do not split information Trisomy-extra chromosome could occur zygote has 47 instead of 46 causing Downs syndrome Monosomy-missing chromosome usually causes death. In women a missing X chromosome causes Turners syndrome Karyotype- a physical way of looking at chromosomes in a specified order. Trisomy 21st chromosome has 3 copies Monosomy 22 chromosomes, missing X Polyploidy- most animals will die from this, many plants thrive with it. Can cause larger fruits and have huge commercial benefits for farmers DNA DNA controls the cells by determining a proteins structure They are needed in muscle, bone, and enzymes DNA contains all information for making proteins for a cell Even a virus, which is made of proteins, contains DNA Structure of DNA Nucleotide- a repeating unit that makes up DNA Contains: Deoxyribose sugar phosphate group Nitrogenous base( 4 possible) Nitrogenous bases Made of a nitrogen ring with other atoms arranged in different orders Purine- a double nitrogen ring Adenine Guanine Pyrimidine- a single nitrogen base Thymine cytosine The DNA molecule is made by the ribose sugar of one nucleotide binding to a phosphate group next to it. Because of the structure of the nucleotide, DNA twists so that the phosphate and ribose will match up Nitrogen base bonding Because DNA is a double helix, made of 2 strands, the nitrogen bases will only bind with the correct match through hydrogen bonding. Adenine with Thymine Cytosine with Guanine Notice it is one of each type of nitrogenous base DNA can store huge amounts of information because it is very long. Since there are only 2 possible choices of how nucleotides (A-T) (C-G) will match up, DNA sequences the information in different orders to code for different genes Can use these sequences to check for evolutionary relationships DNA Replication DNA makes a copy of the chromosome before mitosis and meiosis Starts with an enzyme that breaks the hydrogen bonds between nitrogenous bases and unzips the molecule. Free nucleotides then bind to their matching base and a new chain is formed for each side of the DNA Making Proteins First DNA must be transcribed into RNA. RNA is a single strand of genetic material made from one side of DNA RNA has 4 nucleotides just like DNA, but 1 is different RNA Uracil binds with DNA adenine RNA Adenine binds with DNA thymine RNA Cytosine binds with DNA guanine DNA unzips and free nucleotides join together to form RNA 3 types of RNA Messenger RNA (mRNA) Brings the instructions to make proteins from the nucleus to the cytoplasm Ribosomal RNA (rRNA) Makes ribosomes- where proteins are made Transfer RNA (tRNA) Transfers amino acids to the ribosome to make amino acid chains (proteins) mRNA is the message from DNA, but before proteins can be made the code must be translated. Amino acids are the code used for proteins 20 different amino acids that make up proteins But ONLY 4 nucleotide on RNA?????? To code for a protein, 3 nucleotides are used and are called a codon Each codon represents an amino acid Some codons are instructional Start codons at the front of mRNA Stop codons at the end of the protein section More than one codon can code for the same amino acid How to make a protein 1. mRNA from the nucleus moving into the cytoplasm and then attaching to a ribosome 2. amino acids must be brought to the ribosome by transfer RNA (tRNA) Each tRNA will attach to 1 type of amino acid Each tRNA has an anti codon that will match up with the mRNA code This is how nitrogen bases are translated into amino acids The ribosome will then allow the tRNA to bind to the active site of the mRNA and start a protein, one amino acid at a time. The process starts at a start codon and ends at a stop codon, both are recognized by the ribosome As one tRNA adds its amino acid to the chain, a peptide bond occurs between amino acids to hold the chain together. When a bond has been made the ribosome will then move on down the mRNA to the next active site and continue the process. The used tRNA then returns to the cytoplasm Mutations Mutation- a change in DNA sequence Mutations can be caused by errors in: Replication Transcription Cell division External factors Mutations in reproductive cells A change in sequence of DNA in a gamete If a zygote is made the mutated DNA would become part of the organism This can cause: Problems with protein synthesis, the proteins do not work Death to a zygote because proteins are non functional A positive mutation to help an animal to survive Mutations to body cells Caused by radiation or other external factors Once damaged the cell will continue to replicate with the damaged DNA as long as it can Loss of control because of DNA mutations can cause cancer or other issues because of lack of proteins Point mutations to DNA A point mutation is when a single nitrogenous base is switched with another. This could cause the entire structure of a protein to be changed because the codons would be messed up RUN DOG RUN RUN DOC RUN Frame shift mutation to DNA The deletion or addition of a nitrogen base to a DNA strand This could cause the entire structure of a protein to be changed because the codons would be messed up RUN DOG RUN RUD OGR UN DNA repair There are enzymes that repair DNA as mistakes are made. But even they can mess up. Chromosomal mutations- structural changes to chromosome May break or get lost during division If the break and rejoin they might join backwards Or on a different chromosome Often happens in plants Few chromosomal changes are passed to off spring because zygote dies from missing or wrong placed information