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KEY Name _________________________ Unit 3 Our Cells at Work DNA , Chromosomes, & Genes DNA is a molecule made of base pairs attached to two strands of sugars and phosphates (the “backbone”). The base pairs in DNA are: A pairs with ____ T ____ C pairs with ____ G ____ The order of the base pairs in DNA determine the order that the amino acids are linked together when proteins get built. Proteins are what living things are made up of; your traits (characteristics) are proteins…. which means, your DNA is the instructions to make you! You got these instructions from your biological parents. When a sperm fertilizes an egg, the nuclei combine….so ½ your DNA came from your biological mother, and ½ came from your biological father. Because we have so much DNA, it is organized into chromosomes (as shown in the diagram), which are protected in 46 the nucleus of the cell. Humans have a total of ______ chromosomes in the nucleus of every body cell….which means, ½ of 23 chromosomes came from your biological mother’s egg that, or ____ 23 chromosomes came from your biological (gamete) , and _____ father’s sperm (gamete). A segment (piece) of DNA is a gene. Each gene carries the instructions to build just one protein. Your genome has about 25,000 genes, so there are many genes on each chromosome. Each chromosome you got from your mother “matches” up with a chromosome that you got from your father…..so it is the “combination of instructions” that you received in those 23 pairs of chromosomes that makes you unique. Protein Synthesis (building proteins from the instructions in DNA) Protein Synthesis is the process that causes traits to be expressed…..the process that created your eye color pigments, your skin tissue and color, your muscle, your digestive enzymes, etc. The “instructions” (DNA) are stored and protected in the cell’s nucleus…..but proteins get built outside of the nucleus (at ribosomes). To get the instructions out of the nucleus, another nucleic acid – RNA – is needed….. A gene is transcribed by mRNA (messenger RNA). It does this by “paring up with” the genetic code on DNA – the only difference is there are no “Ts” in RNA, so, when there is an “A” in DNA, RNA will pair that with a “U”. C’s still pair with G’s. Once transcribing is complete, the instructions to build that protein are carried by mRNA out of the nucleus to a ribosome. When mRNA arrives at the ribosome, tRNA (transfer RNA) arrives carrying an amino acid. When tRNA locates the “drop off point” by reading the code on mRNA, it lets go of the amino acid so it can be linked to the others. A chain of amino acids is a protein. If this were a skin cell, the protein made might be the pigment melanin that gives your skin color. If the cell is a muscle cell, the protein made might be “myosin or actin” which are the proteins that muscle tissue is made of. If the cell was in your mouth, the protein made might be an enzyme in your saliva that helps break down food. Review: 6. Protein Synthesis Every organism that reproduces sexually has an even number of chromosomes in the nucleus egg of each of their body cells…..this is because ½ of them came from the mother’s ______ and sperm 46 ½ came from the father’s ___________. For example, humans have a total of ______ 23 came from the sperm, and ____ 23 came from the egg. chromosomes in every body cell -- ____ Chromosomes neatly package all of the DNA of that organism, and DNA is the instructions to make all of the proteins that make up that organism and allow that organism to function. What is the relationship between DNA , genes , and chromosomes? Both chromosomes and genes contain the molecule DNA. Chromosomes are structures that contain condensed DNA. Genes are specific sequences of DNA that code for proteins. Because genes contain DNA, genes are also found in chromosomes. What is the relationship between proteins, genes, and traits (characteristics)? Genes code for proteins which are expressed as traits based on the function of those proteins. For example, a gene coding for freckles will produce proteins that will express that trait. Proteins Synthesis Name the process that causes traits to be expressed in offspring: __________________ This is how it works: 1. A gene (segment of DNA) = GTC ATT GCA 2. …..is transcribed by mRNA = __CAG UAA CGU__ ; this takes place in the _nucleus__ of the cell. 3. ….mRNA caries the copy out of the nucleus to a _ribosome_ 4. ….at the ribosome, tRNA arrives carrying an _amino___ __acid____ that will be linked together to make a ___protein_______ 5. Proteins are your traits/characteristics. What is a characteristic of DNA that determines what protein is made? Sections of the DNA molecule which “code” for specific proteins are called genes. Genes have a specific starting point and ending point so the gene produces the exact same RNA every time in an individual. Differences in base pair sequences between individuals for any specific gene are called alleles. Different alleles “code” for different proteins which causes different characteristics in a population. So, describe how a rabbit ends up with pink eyes. The gene that determines eye color produces the RNA which is then translated into the protein that creates the red eye pigment. ____ COE: “It’s in the Genes #1” Mutations DNA Mutations are changes in _____ Mutations are fairly common in DNA, and, luckily most are harmless. Mutations can occur in several ways: Random errors during DNA replication – these are fairly common and occur when a nucleotide is substituted, inserted, or deleted from a gene. Since mRNA will copy the error, an incorrect amino acid will be inserted when the protein is being built. Exposure to certain chemicals and radiation can also cause DNA mutations. If a mutation occurs in a body cell of an organism…..like a skin cell, liver cell, muscle cell, bone cell, etc., it can cause “bad proteins” to be built and cause a defect in those cells and tissues. A body cell mutation will only impact the individual with the mutation….they _____ will ______ be passed on to the offspring!!! not If a mutation occurs in a gamete, or sex cell (sperm or egg) then it will not affect the “parent organism”, but the mutation ___________ cause a defect in an offspring – again, because could “bad proteins” could be made from the error in the “instructions” (DNA). Sometimes mutations can benefit an individual. So, if the gamete mutation resulted in a new trait that made that individual more likely to survive and reproduce, then that mutated gene would most likely be passed on to the next generation. …….and the next generation…….and the next….. If that gene gets passed on to enough individuals (through several generations), over time, most of the population will express this beneficial gene mutation --- so the population would have “changed”…..or evolved. Review: 7. Mutations DNA Mutations are changes in ___________ Original DNA strand: Mutated DNA: Mutated DNA: Mutated DNA: ATC GGC AAC G ATC GTC AAC *compare all mutations to the original DNA ATC GGA CAA C G ATG GCA AC (A inserted between G and C) Type of mutation: Insertion ___________________ Original DNA Strand: CGT AAT CTG (T substitutes for G) Type of mutation: Substitution ___________________ (G deleted between G and C) Type of mutation: Deletion ___________________ All of the mutations above are called point mutations. CGT TAT CTG Show what a substitution might look like: __________________________ CGT ATC TG Show what a deletion might look like: _____________________________ CGT AAA TCT G Show what a insertion might look like: ____________________________ An original DNA strand and the same strand after a mutation are shown below. Describe the type of mutation that has occurred in the strand. DNA: Mutated DNA: TAC GGT CCA TAC GTC CA In your description, be sure to: Identify the type of mutation Describe one way this mutation can occur Type of Mutation: The mutation is a type of point mutation called a deletion. In the example, a G was deleted from between the G and T. One way this mutation can occur: The following mutagens may cause mutations like the one above: 1) Chemical (smoking, alcohol, diet) 2) Physical (UV light, X-rays, gamma rays) 3) Infectious agents (HPV) A local pond has been receiving fertilizer run-off from a new farm nearby; the pond is now surrounded year around with green, lush vegetation. A mutation occurred in a duck egg resulting in offspring with a darker, greener coloration. Describe how this trait could allow the offspring to survive and reproduce in its pond ecosystem. A darker, green coloration may enable the offspring to avoid predators (camouflage) and or to better catch prey. This adaptation would both help the offspring stay alive longer and be better fed (healthier) than ducks of other coloration within the population. This may result in the dark-green ducks having a higher rate of reproduction relative to other colorations (unless of course dark green is not a desirable trait regarding sexual selection). Imagine that there is a new mutation in a skin cell (body cell) of a frog. What effect could this mutation have on this organism (the frog)? If the same frog has a mutated sperm (gamete) what effect could this mutation have on this organism (the frog)? Effect of body cell mutation on the organism: Most mutations are neutral, meaning they produce no effect. However, a possible effect of a gene mutation in a body cell of the frog would be to disrupt the cell’s growth cycle, perhaps causing the cell to become cancerous. This may result in the death of the frog. Effect of sperm mutation on the organism: A mutation in a sperm cell may cause that gamete to become sterile. However, since many more healthy sperm are being produced by the frog, the mutation will most likely not have any effect on the reproductive success of the organism. On the other hand, a mutation could cause the sperm to become more productive, like making the sperm swim faster than others. If this sperm fertilizes an egg, the resulting offspring would inherit this mutation. Imagine that there is a new mutation in a skin cell (body cell) of a frog. What effect could this have on the organism’s offspring (the baby frogs)? Imagine that there is a mutation in a sperm (gamete/sex cell) of the frog. What effect could this have on the organism’s offspring (the baby frogs)? Effect of body cell mutation on the offspring: Because a body cell was affected, there would be no heritable effect on the offspring. The only way offspring could be affected is if the skin cell became cancerous and killed the parent while the offspring were still dependent on the parent for survival. Effect of gamete mutation on the offspring: Most DNA does not code for proteins or have any regulatory function. Therefore, most mutations will have no effect on the offspring. However, a mutation in a gamete’s gene that regulates some aspect of development may produce a visible variation in the offspring’s phenotype. For example, an inherited mutation could change the number or position of spots on the skin of a frog. Now let’s imagine that this frog’s sperm mutation gives the offspring the ability to produce a new skin protein that tastes really nasty. How can this mutation help the baby frogs survive and reproduce in their environment? Any predator that happens to eat a bad-tasting baby frog will likely remember the experience, and avoid eating any frogs that look like they might taste bad. Frogs under reduced predation pressures will have more opportunities to move about and feed themselves. These baby frogs will have a better chance of growing to a breeding age compared to tasty-looking frogs. How can that one mutation eventually benefit the entire population of frogs in this particular pond ecosystem? The process of natural selection could increase the population of nasty-tasting frogs and any frogs that mimic them. Because the mutation produces a nasty taste, predators that experienced it (the taste) would avoid eating any frog that closely resembles the bad tasting ones. With less predation, more frogs that look like they taste bad will survive and reproduce, increasing the frog population in the pond. ____ COE: “It’s in the Genes #2” How New Cells are Formed Before a cell can divide, it must make another copy of its DNA – so that the new cell has all of the DNA, too! This process is called DNA Replication… After replication, chromosomes look like this; the copy stays “attached” until it is time to for the cell to divide…then one copy goes to each cell. Mitosis Mitosis is the way you get more body cells for growth, development, repair of damaged tissues, replacing dead cells, etc. DNA replication occurs before a cell divides because there needs to be two copies of each chromosome --enough for each new cell to get a “full set” So, during mitosis, a cell that starts with 4 chromosomes will divide one time to create two cells, each with 4 chromosomes. ….so an identical cell is created. From the time an egg is fertilized, the organism grows and develops by creating new cells – and the process that makes new cells is mitosis. Mitosis is an organized way to divide the chromosomes into two separate nuclei….when this is done, the cell can divide. Different organisms have different numbers of chromosomes in their body cells: If that is true, then how come gorillas have the same number of chromosomes as potatoes (48); pigs have the same number as cats (38); and chickens have the same number as dogs (78)? Meiosis Meiosis only takes place in specialized cells located in reproductive structures of organisms. After DNA replication, the cell divides twice to create four cells, each with ½ the original chromosome number. So, meiosis is the organized way to reduce chromosome number so that each gamete only has one copy of each chromosome. This produces the gametes (sperm & egg). So, our organism with 4 chromosomes in every body cell, will produce gametes containing 2 chromosomes. Then, when the sperm fertilizes the egg, a new organism with 4 chromosomes will be produced. There are three events that take place during meiosis that lead to unique combinations of genes in the gametes: 1. Independent Assortment – the way that the chromosomes line up to start meiosis is completely random…..and then when they separate into the gametes, it is random as to which chromosome goes to which gamete. So it’s kind of like “shuffling a deck of cards and dealing out half the deck”……each gamete gets a different combination of genes. 2. Crossing Over – This occurs when the chromosome pairs first line up next to each other at the start of meiosis……some of the chromosomes “swap parts”, creating new combinations of genes 3. Mutations – it is possible for random mutations to occur during DNA replication that precedes meiosis; these “mistakes” can then end up in the egg or sperm and passed on to the offspring. 8. Mitosis Describe mitosis in a goldfish cell; or how a goldfish makes new body cells: 94 1. Each gold fish cell starts with ______ chromosomes in each body cell replication 2 copies of 2. DNA _______________________ has to occur first so there are ____ each chromosome before the cell divides. 3. The cell makes sure that the chromosomes get separated correctly then divides one _______ time 4. After mitosis, there are _____ cells, and each one has _____ chromosomes in the 2 94 nucleus. 9. Meiosis egg sperm Meiosis is the type of cell division that produces gametes, or ___________ and ________. This only takes place in very specialized cells in the organism’s body, and it reduces the total chromosome number by ½. How many chromosomes would be in the sperm or eggs of each of the following organisms? 39 dog ____ 3 ____ mosquito 19 cat ____ 23 human ____ 9 cabbage ____ Describe meiosis in a goldfish; or how a goldfish makes gametes: 94 1. Each gold fish cell starts with ______ chromosomes in each body cell, and in the specialized cells that produce sperm and egg. replication 2 copies of 2. DNA _______________________ has to occur first so there are ____ each chromosome before the cell divides. 3. The cell divides __________ twice 4. After meiosis, there are _____ 4 cells, and, in a goldfish, each one has _____ 47 chromosomes in the nucleus – which is ____ the original chromosome number. 1/2 Describe one event that takes place during meiosis that results in “unique” sperm or eggs. 1) Chromosome tetrads are able to independently assort during metaphase I of meiosis. For example, independent assortment in humans can produce 223 new chromosome combinations, or 8,388,608 unique cells. 2) Crossing over of non-sister chromatids in prophase I produce an almost limitless number of unique DNA recombinants. Coupled with independent assortment, the number of unique cells that can be produced is inexhaustible. Genes are pieces of DNA that code for specific proteins. You have your eye color because you inherited certain genes from your parents. We often describe genes with letters, and alleles are different forms of the same gene. You may have inherited a dominant brown eye allele (B) from one parent, and a recessive blue eye allele (b) from the other parent, so the combination of genes you inherited (your genotype) is Bb. Mom and Dad both have brown eyes (BB or Bb); two of their kids have brown eyes (BB or Bb), and two of their kids have blue eyes (bb). What is one event that occurs during the formation of egg or sperm (meiosis) that makes it possible for these two brown-eyed parents to have kids with brown eyes and kids with blue eyes? Mom and Dad must both be Bb. One event that makes it possible for blue eyes to appear in their children is the segregation of chromosomes during metaphase I and metaphase II that places either a B (brown allele) or a b (blue allele) in each sperm or egg cell. The second event is the complete randomness by which sperm and egg unite during fertilization. Both the B and b alleles from each parent have an equal chance of coming together in the formation of a zygote. Fertilization – Creating unique new organisms through sexual reproduction Fertilization sperm _____________________ occurs when the male gamete (___________) combines its genetic material (chromosomes) with the female gamete (_______) to egg create a fertilized egg, called a zygote. Each gamete only has ____ 1/2 set of chromosomes, so when they unite, they restore the original chromosome number, in the case of 46 (or ____ 23 pairs) humans, that number is _____ In the case of a dog…… 39 39 78 Review: 10. Fertilization Punnett Squares are used to show the probability of outcomes if fertilization were to occur. Brown eyes (B) are dominant over blue eyes (b). Mom and Dad both have brown eyes; 2 of their kids have brown eyes, and two of their kids have blue eyes. What is one event that occurs during fertilization that makes it possible for these two brown-eyed parents to have kids with brown eyes and kids with blue eyes? Explain your answer. Sperm Both parents must be Bb. B b B BB Bb b Bb bb Egg If a B sperm fertilizes any egg (B or b), the offspring will have brown eyes (75% chance). If a b sperm fertilizes a b egg, the child will have blue eyes (25% chance) ____ COE: “Bear Crossing #3” (Review 8, 9, & 10 before starting) Genetics The genes you inherit from your parents can come in different forms, or ___________. You only alleles inherit one allele from each parent, so the combination you inherit will determine which proteins are made…..these are your traits. Some alleles are completely dominant, which means, that if it is present, it will be expressed; we use a _______________ letter to represent the dominant allele. Some alleles are recessive, which means capital that the trait will not be expressed if a dominant allele was also inherited. The only way that a recessive trait would be expressed is if a recessive allele was inherited from both biological parents. We use a lower-case letter to represent recessive alleles. The combination of alleles that an organism inherits is its genotype. So a dominant genotype for a given trait could be _____ AA or _____; Aa a recessive genotype would be ______. aa If the two alleles in the genotype are the same, it is called homozygous; so _____ AA is a homozygous dominant genotype. An example of a homozygous recessive genotype would be aa ______. If the two alleles are different, the genotype is heterozygous…..he may have inherited a brown eyed allele (B) and a blue eyed allele (b), but his eyes will be brown because brown is dominant (Bb). Phenotype is what trait is expressed…or “what it looks like” because of the genes it inherited. So “blue eyes”, “long fur”, “spotted wings”, “yellow petals”, etc. are all phenotypes. Practice: Let’s say that in a certain butterfly, blue wings (B) are dominant over red wings (b). Use a Punnett Square to show the possible outcomes (genotypes and phenotypes) of cross between a homozygous blue winged bug and a red winged bug. Egg Sperm B B Homozygous dominant blue wings = BB Homozygous recessive red wings = bb b Bb Bb Genotypes: 100% Bb, or heterozygous (hybrid) b Bb Bb Phenotypes: 100% Blue wings hybrids The offspring produced in this example are called ____________, or “offspring of different parents”. Now, cross two of the hybrids and describe the possible genotypes and phenotypes of the offspring. Egg Sperm B b Heterozygous parents with blue wings = Bb B BB Bb Genotypes: 25% BB; 50% Bb b Bb bb Phenotypes: 75% Blue wings; 25% red wings In a certain breed of llama, black spots (S) are completely dominant over fur with no spots (s), and long floppy ears (E) are completely dominant over short, pointy ears (e). Cross a spotted, long floppy eared male llama (homozygous for both traits) with a female llama that has no spots and short, pointy ears. Describe the possible genotypes and phenotypes of the offspring. Sperm SE ssee Genotype of female: ________ Egg SSEE Genotype of male: ________ SsEe se 100% SsEe Genotypes of offspring: _______ 100% Black spots with floppy ears Phenotypes of offspring: __________________ Note: Since there was only one type of sperm and one type of egg possible, it was not necessary to use more than one box of the Punnett square. The offspring have grown into adult llamas. One llama, Lolla, is ready to reproduce. What are the possible allele combinations that could be found in Lolla’s eggs after the process of meiosis? SsEe Lolla’s genotype: _______ Lolla’s eggs: SE Se sE se Review: 11. Genetic Crosses A dihybrid cross means we are looking two traits, and the probability of outcomes if fertilization were to occur. In guinea pigs, brown fur (B) is dominant over white fur (b) and Pink eyes (P) are dominant over blue eyes (p). A male guinea pig is homozygous dominant for both traits --- he has brown fur and pink eyes. He is being bred with a female that is homozygous recessive for both traits – she has white fur and blue eyes. BBPP Male’s genotype: ____________ bbpp Female’s genotype: __________ When sperm and egg are formed, each will only have one copy of each “allele” (gene), but each has to have a “fur color gene” and an “eye color gene”….. BP Genes in every sperm: _________ bp Genes in every egg: __________ BbPp What will the genotype of the offspring be when the sperm fertilizes the egg? __________ 100% Brown fur and pink eyes What will the phenotype of the offspring be? _________________________________ Now let’s imagine that the offspring are old enough to mate. We will take one female from this litter, and mate it with a male that has white fur and blue eyes. What are the parent genotypes? bbbp Male’s genotype: _______________ BbPp Female’s genotype: ___________ bp Genes in every sperm: ___________ Possible gene combinations in eggs: BP ____ Bp ____ bP ____ bp ____ Determine the possible genotypes and describe the odds of each phenotype for their offspring: Sperm: bp Eggs: 25% Brown w/ pink eyes: _______ 25% Brown w/ blue eyes: _______ 25% White w/ pink eyes: _______ White w/ blue eyes: _______ 25% BP BbPp Bp Bbpp bP bbPp bp bbpp Note: Since there was only one type of sperm, it was not necessary to use more than one column of boxes in the Punnett square. In the next pair to breed, the male is homozygous dominant for fur color and heterozygous for eye color. The female is white with blue eyes. BBPp Male’s genotype: _______________ bbpp Female’s genotype: ___________ Possible gene combinations in sperm: bp Genes in every egg: ___________ Bp ____ ____ BP ____ ____ Determine the possible genotypes and describe the odds of each phenotype for their offspring: Sperm: Eggs: 50% Brown w/ pink eyes: _______ 50% Brown w/ blue eyes: _______ 0% White w/ pink eyes: _______ 0% White w/ blue eyes: _______ bp BP Bp BbPp Bbpp Children inherit traits from their biological parents, because traits are encoded in the DNA that they receive from the sperm and egg. Describe the process that will cause these traits to be expressed in the newborn baby. The process which codes for traits in a newborn baby is called protein synthesis. During protein synthesis, activated genes transcribe mRNA within a cell’s nucleus. mRNA then makes its way into the cytoplasm where it is translated into proteins by ribosomes. Ribosomes “read” the sequence of codons in mRNA and assemble amino acids that correspond to that sequence. It is the sequence of the amino acids in a protein that determine the protein’s function. Humans, like other animals, eat food to acquire energy, attain the required molecules to build and repair tissues, etc. Describe how you transform the energy from the salad you ate for lunch into a form of energy that your cells can use for life functions such as growth and development. Identify the process that transforms the energy in plants into energy that you can use for life functions Identify the molecule that contains energy in plants and the molecule that contains the energy that you can use The process that plants utilize to transform energy that can be used for life functions is photosynthesis. Through photosynthesis, plants store energy from sunlight in the chemical bonds of glucose. When we eat plants or eat animals that eat plants, we obtain plant-made glucose. We then “burn” glucose during cellular respiration to release its energy. Some of the energy in glucose is released as heat. The rest is stored in the chemical bonds of ATP. ATP is what our cells use to carry out metabolic functions. Many plant products can be used to make biofuels, like ethanol, that are added to gasoline (a fossil fuel). Describe two similarities and differences between cellular respiration in humans and the burning of fossil fuels, like gasoline. Similarities: Both processes release energy stored the chemical bonds of fuels. Both processes require oxygen to burn the fuel. Both processes release heat, water, and carbon dioxide. Differences: Cellular respiration occurs in cells; burning fossil fuels occurs in machines, like cars. Cellular respiration uses glucose; burning fossil fuels uses fuels like oil, coal, and natural gas. Cellular respiration produces ATP; burning fossil fuels produces ash and soot. Cellular respiration releases small amounts of heat; burning fossil fuels releases large quantities of heat. ____ COE: “Planning a School Garden #4” ____ COE: “Columbia White Tailed Deer #3”