Bio Test Meiosis and Mutation

There are 3 mai types of specialized cells in your body ● ● ● ● ● ● ● ● A specialized cell is a cell that has developed specific features and functions to perform a particular job in the body. Somatic Cells ko ○ are body cells that make up most of your body tissues and organs ○ DNA in your body cells are not lpassed onto your children germ cells ○ Germ cells are in your reproductive system ■ ■ as ovaries or testes ■ Germ cells develop into gametes Gametes are sex cells ○ ova or eggs in the female ○ spermatozoa or sperm cells in the male ○ DNA in gametes can be passed onto your children Each species has a fixed number of chromosomes in its body cells and in its DNA and cells, but the number in sex cells is half the number in body cells. ○ ○ ○ ○ The chromosome number is not related to complexity of an organism The number of chromosomes just depends on how the DNA is organized, not how advanced or complicated the organism is. each of your body cells have a set of 46 chromosomes, which come in 23 pairs ■ they are not genetically identical to one another because one comes from each ur mom and the other from your dad ■ cells use both sets of chromosomes to function properly ■ But they pair because they carry the same type of genes for characteristics in different versions. ■ ● We have different types of cells not because they have different DNA, but because they use different parts of that DNA ● That’s called gene expression, the process by which a cell turns certain genes “on” or “off” depending on the specific function it needs to perform. For example, a red blood cell turns on the genes responsible for producing hemoglobin, which helps it carry oxygen. ● ● ● For example, red blood cells have the same DNA as nerve cells, but they are different because they use different parts of the same DNA Autosomes ● ● There are two types of chromosomes: auyosomes and sex chromsomes Autosomes are the chromosomes that are not involved in determining the sex of an organism ● In humans, there are 22 pairs of autosomes, making a total of 44 autosomes. The last pair is not an autosome since it is a sex chromosome ● Each pair of chromosomes in your body is referred to as a homologous pair. ● They have the same structure and carry the same genes responsible for making the same traits. These genes are even located at the same positions on the chromosomes. ● However, the genes they carry are different versions, called alleles, and these alleles determine specific characteristics. ● One chromosome from each homologous pair is inherited from your mother, and the other is inherited from your father. They are similar in length, structure, and appearance. . ● ● ● ● chromosomes are organized from the largest to smallest. The largest pair of chromosomes is chromosome pair 1 chromosome pairs 1-22 make up your autosomes, chromosomes that contain genes for characteristics not relate to the sex of the organism homologous chromosomes are not identical, but they are very similar. Here’s why: ● They have the same genes arranged in the same order. ● But they may carry different versions of those genes (from the mother and the father). ● Sex Chromosomes ● ● ● ● ● Sex chromosomes make up the 23rd pair of chromosomes Most sexually reproducing species have sex chromosomes that control the development of sexual characteristics humans have 2 different sex chromosomes; X and Y In all mammals, including humans, an organism’s sex is determined by the XY system ○ an organism with two X chromosomes is female ○ an organism with an X and Y chromosome is a male Although X and Y chromosomes pair with each other, they are not homologous ○ the X chromosome is the larger sex chromosome and contains more genes, even some that are unrelated to sexual characteristics ○ the Y chromosome is the smaller sex chromosome that contains fewer genes that direct the development of the testers and other male traits ○ it is the smaller chromosome and carries fewest genes Diploid and Haploid ● Body cells and gametes have different number of chromosomes ● Body cells are diploid and gametes are haploid ● Diploid is when a cell carries 46 chromosomes, while haploid is when a cell carries only 23 chromosomes ● ● Diploid means that a cell has two copies of each chromosome : one from the mother and the other from the father ● diploid cells be represented in 2N, while haploid are represented as n ● haploid means that a cell only has 1 copy of each chromosome ○ Only gametes are haploid ○ ○ ● ● ● ● ● It means that the gamete does not carry pairs of chromosomes, just 1 of each kind, making 23 chromosomes No homologous pairs Sexual reproduction involves the fusion of two gametes: an egg and a sperm ○ results in offspring that are a genetic mixture of both parents when fertilization occurs, the nuclei of the egg and sperm fuse together to form one nucleus ○ this nucleus must have the correct number of chromosomes for a healthy new organism to develop ○ This is why egg and sperm cells have half the normal number of chromosomes each human egg or sperm cell has 22 autosomes and 1 sex chromosome, which is always an x, so a total of 23 chromsomes in the egg, the sex chromosome is always an X chromosome In the sperm cell, the sex chromosome can be an X or Y chromosome Chromosome Number ● Most organisms need the correct number of chromosomes to survive ○ if a chromosome is added or missing in the gamete during meiosis, it causes problems or diseases ○ When an organism has extra or missing chromosomes, it means there is a gain or loss of a whole chromosome (the entire structure, not just one chromatid). ○ PThis condition is called aneuploidy. ○ Definition of aneuploidy: ○ Aneuploidy is the presence of an abnormal number of chromosomes in a cell — either missing one or more chromosomes, or having one or more extra chromosomes. ○ When an organism has extra or missing chromosomes, it means the error happened in the gamete during meiosis. ○ ○ ● ● When the gamete receives extra full sets of chromosomes, during meiosis, it can create a new species, especially in plants. here’s how: An extra full set means the whole set of chromosomes (all of them) is copied again. ● ○ Normally, a gamete (sperm or egg) is haploid (1n), meaning it has one copy of each chromosome. ○ Sometimes, due to errors in meiosis, a gamete can end up with two copies of chromosomes (diploid, 2n) instead of one. ○ If this diploid gamete combines with a normal gamete (haploid, 1n), the result can be an organism with three sets of chromosomes (triploid, 3n) or even four sets (tetraploid, 4n). ○ This condition is called polyploidy, where an organism has more than two full sets of chromosomes. ○ Polyploidy is common in plants and can sometimes help create new species because the extra chromosome sets can make the organism different from its parent species. ○ ● Tetraploidy (4n) means the organism has four complete sets of chromosomes instead of two. ○ So instead of 2 copies of each chromosome, it has 4. ○ \This is common in plants but very rare in animals. Meiosis Vs Mitosis ● ● Germ cells in the reproductive system undergo meiosis to form gametes meiosis is a form of nuclear division that divides a diploid cell into haploid cells. ○ Because of this, it is also referred to s “reduction division” ○ essential for sexual reproduction ● Mitosis produces genetically identical cells while Meiosis produces genetically unique cells Mitosis results in diploid cells while Meiosis results in haploid cells Mitosis takes place throughout the organism's lifetime while meiosis only at certain times in an organism life cycle Mitosis is involved in asexual production while meiosis is involved in sexual reproduction ● ● ● ● Mitosis is a process that only occurs in body cells ○ produces daughter cells that are genetically identical to parent cell ○ in meiosis, DNA is only copied and divided once ○ both parent and daughter cells are diploid ○ ● ● ● ● Mitosis is used for development, growth, and repair in all types of organisms ○ also used for reproduction in asexually producing eukaryotes Meiosis occurs in germ cells to produce gametes DNA is copied once but divided twice makes genetically unique haploid cells from a diploid cell these haploid cells then undergo more processing in the ovaries of tested, forming mature gametes Meiosis ● ● ● ● ● Is a form of nuclear division that creates 4 haploid cells from one diploid cell involves 2 round of cell division: Meiosis I and Meiosis II each round has 4 phases Each half of the chromosome is called a chromatid ○ sister chromatids refer to the duplicated chromosomes that are attached at the centromere Homologous chromosomes are divided in meiosis I and sister chromatids are divided in meiosis II. Steps of Meiosis ● ● ● Before meiosis begins, DNA has already been copied in S phase After DNA replication, a diploid cell still has 46 chromosomes. Before DNA replication, each chromosome consisted of a single chromatid. After replication, the chromatids are duplicated and now attached to the centromere, forming duplicated chromosomes that are in an x shape. ● Meiosis I divides homologous chromosomes, producing two haploid cells with duplicated chromosomes (which were already duplicated during interphase). ● ● ● ● ● ● Prophase I: ○ the nuclear membrane breaks down ○ and the centrosomes and centrioles move to opposite sides of the cell ○ spindle fibers start to assemble The duplicated chromosomes begin to condense into an x shape (were in the form of chromatin) Each chromosome binds and pairs with its corresponding homologous chromosome they pair up precisely, gene for gene, down their entire length ○ the sex chromosomes also pair up ■ ● ● ● ● ● The homologous chromosomes in the diploid cell were not next to each other/ paired up before meiosis, they were just in the same nucleus Each homologus pair carries the same genes, but different variations When the homologous chromosomes pair up, they cross over, ○ Meaning, segments of chromatids from each chromosome exchange alleles. ○ ■ alleles are different versions off the same gene on the homologous chromosome pair The alleles the exchange on every chromosome, a random and result in different gene combination, results in genetic variety and explains why children are different from their parents and sibilings Metaphase I: ● ● ● ● ● ● ● ● ● ● ● ● The spindle fibers longate The homologous chromosomes , (meaning the 2 x shaped chromosomes) are randomly lined up along the middle of the cell by spindle fibers in pairs the result is that 23 chromosome pairs, (some from mother and father) are lined up along each side of the +cell equator one chromosome from each homologous pair can be on the right side of the equator, and the other can be on the left side. This arrangement allows chromosomal combinations. Each gamete ends up with a unique mix of chromosomes — some from the mother, some from the father — creating lots of genetic variety. This random orientation of 23 pairs results in 2^23 = 8,388,608 possible combinations, creating genetic diversity. Anaphase I: the paired homologous chromosomes separate from their corresponding pair because spindle fibers shorten They move toward opposite sides of the cell. The sister chroma-tids remain together during this step and throughout meiosis I. Telophase I: ● ● ● ● The nuclear membrane forms again in some species, the spindle fibers disassemble, and the cell undergoes cytokinesis. The end result is two haploid cells that each have a unique combination of 23 duplicated chromosomes coming from both parents note: there are no more homologous pairs ● In both mitosis and meiosis I, the chromosomes in a diploid cell exist as homologous pairs (one from the mother, one from the father), ○ but they are not physically paired together. ○ In mitosis, these chromosomes are not paired up at all, whereas in meiosis I, they eventually pair up physically during prophase I and then are separate ● Meiosis II: ● Divides the sister chromatids and results in undoubtedly chromosomes ● DNA is not copied again between these two stages Prophase II: ● The nuclear membrane breaks down ● centrosomes and centrioles move to opposite sides of the cell ● spindle fibers assemble Metaphase II: ● Spindle fibers align the 23 chromosomes at the cell equator ● each chromosome still has 2 sister chromatids at this stage Anaphase II: ● The sister chromatids are pulled apart from each other and move to opposite sides of the cell Telophase II: ● The nuclear membrane forms around each set of chromosomes at opposite ends of the cell ● the spindle fibers break apart ● cell undergoes cytokinesis ● the result is 4 haploid cells with a combination of chromosomes from the mother and father ● ● Mature gametes ● Haploid cells are the end of meiosis but are incapable for fertilization until they are processed ● They undergo gametoggeneis , the production of gametes ● the stages of gametogeneis differ between sexes sperm cell formation: ● The sperm is much smaller than the egg cell ○ its small size is importnat for its function bc it travels a long distance to fertilize the egg ■ ● the small size allows the sperm to move quickly and efficiently The sperm’s main contribution to an embryo is DNA ○ it carries half the genetic material required for the formation of a new organism ● sperm formation starts with a round cell and undergoes significant changes to be capable of movement ● During sperm development, DNA is tightly packed into the head, which makes it more compact and protected ○ ensures the genetic material remains intact during the sperm’s journey to the egg ● much of the cytoplasm is lost during sperm formation, resulting in a smaller, more efficient cell ● The sperm develops a tail (flagellum) that acts as a propeller, allowing the sperm to swim rapidly towards the egg ● The sperm’s neck region is packed with mitochondria, which provide energy required for the flaguellum’s movement ● New proteins are added to the sperm’s cell membrane for recognition or interaction with the cell during fertilization Egg cell formation (oogenesis) ● The formation of an egg begins before birth, inside the developing body of a female embryo ○ process is not finished until that egg is fertilized by sperm years later ○ includes period of active development and long period of inactivity ● an egg gives its fair share of DNA to an embryo ○ also gives organelles, molecular building blocks, and other materials an embryo needs to begin life ● only one of the four haploid cells produced by meiosis actually becomes an egg ○ That cell that becomes the egg receives the most organelles, cytoplasm, and nutrients. ○ ● The rest of the cells are broken down and called polar bodies Inside the egg, certain important molecules (like proteins, RNAs, etc.) are located in specific areas and not spread out equally. ○ The uneven distribution helps embryo cells specialize into types like muscle or nerve cells during development. ○ ● When the egg is formed in meiosis II, three extra small cells are also made. ○ These are called polar bodies. They don’t get much cytoplasm or nutrients—just a little DNA—so they don’t become eggs and eventually break down. ● In many organisms (like humans), the polar body made during Meiosis often doesn’t divide again in Meiosis II—it just stays as it is and breaks down. Mutations ● A Mutation is a change in an organism’s DNA. ● Typically, mutations that affect a single gene occur during replication. ● Genes are specific regions of DNA that contain the instructions for building (or coding for) proteins. ● ● A mutation is a change in the nucleic acids. ○ Since mutations change the DNA sequence, they can affect an organism’s traits. ● Mutations that affect a group of genes or an entire chromosome happen during meiosis. ● Types of mutations: ○ Substitution: where the wrong base is added. ○ Insertion: an extra base is added. ○ Deletion: a base is removed. ○ Insertion and deletion mutations have the potential to be especially dangerous. ○ Insertion and deletion only typically occur in frameshift mutations Types of Mutations: ● Point mutation: A mutation where one nucleotide is substituted for another. ○ This means an incorrect nucleotide is placed where a correct one should be. ○ Point mutations do not involve insertions or deletions. Only substitution occurs. ○ It may permanently change an organism’s DNA. ○ It may change 1 amino acid during translation, resulting in a different protein. ○ If a substituted amino acid differs from the original one in size or polarity, the mutation could affect protein folding and affect the protein’s function. ● However, an incorrect amino acid might have little effect on a protein if it has about the same size or polarity as the original amino acid. ○ For ex, hemoglobin is a protein in your RBC that helps you carry oxygen ■ in the disorder sickle cell anemia, the gene that codes for hemoglobin in mutated ■ makes it difficult for red blood cells to carry oxygen bc its shape is affected ● Frameshift mutation: Involves the insertion or deletion of a nucleotide in the DNA sequence. ○ It usually affects a polypeptide much more than a substitution. ○ It shifts the entire sequence following the mutation by one or more nucleotides. ○ This change throws off the reading frame, which results in codons that code for different amino acids ○ ○ It may change more than one amino acid during translation, resulting in a different protein. ● A nucleotide sequence loses its meaning when an insertion or deletion shifts all the codons by one nucleotide. Gene mutations: ● Gene Mutations can have a big effect on an organism: ○ ○ coding region is a part of a gene (specifically part of the DNA) that contains the instructions for making a protein. ● ■ If a change happens in a coding region responsible for making an enzyme’s active site, it can cause a mutation, making the enzyme not be able to bind to its substrate. ● Active site: The part of the enzyme where the substrate (the molecule it acts on) binds and undergoes a chemical reaction. ● Also, a mutation causing an incorrect amino acid far from the active site (where the substrate binds) might have little effect on the enzyme’s function, especially if it doesn’t change the enzyme’s overall structure. ● ○ A mutation in a gene of DNA alters the mRNA sequence, which then changes the sequence of amino acids during protein production. This can lead to a different or nonfunctional protein. ● If a mutation happens in a noncoding region of DNA, it can still cause problems. ● A noncoding region is a part of DNA that does not code for proteins. ● One way a mutation can cause problems is by creating a premature stop codon. ○ This shortens the mRNA strand, which can lead to no protein being made or to a broken, nonfunctional protein. ● Another way is if the mutation affects a regulatory region — the part of DNA that controls when a gene is turned on or off. ○ A mutation here can make a gene constantly active, even when it shouldn’t be. ○ This leads to the production of too much of a protein, overwhelming the normal balance in the cell. ● Changes like these can disrupt the cell’s normal functions and negatively affect the organism’s health, development, or survival. ● However, many gene mutations do not affect an organism’s phenotype: ○ A phenotype is the observable traits of an organism, like eye color or height, ○ ○ Since many codons code for the same amino acid, some substitutions have no effect, especially those occurring in the third nucleotide of a codon. ○ A mutation that does not affect the resulting protein is called a silent mutation. ○ an incorrect amino acid might have little effect on a protein if it has about the same size or polarity as the original amino acid or if it is far from an active site. ● If a mutation occurs in a non-coding region, such as an intron (which does not code for proteins), it may not affect the encoded protein at all. Chromosomal mutations Here’s the information you provided with a structured format: ● Some Mutations can disrupt chromosomal structure or number: ○ If the structure of a chromosome is altered, it is called chromosomal aberration. ● Chromosomal mutations affect a lot of genes and tend to have a big effect on an organism. ● A mutation may break up a gene, which could make the gene no longer work, or it could make a new hybrid gene with a new function. ● ● Types of structural chromosomal mutations: ○ Deletion: A small segment of DNA is removed, resulting in a smaller chromosome. ■ If the segment has important genes, the genetic information is lost, leading to severe abnormalities. ○ Duplication: A segment of the chromosome is duplicated, making the chromosome longer. ■ ○ This results in an abnormality in the organism. Inversion: Two segments on the same chromosome flip or exchange their location, becoming inverted. ■ ○ It may or may not be harmful depending on the type of gene flipped. Insertion: A segment of a chromosome is removed and inserted into another chromosome. ■ ○ Both chromosomes will change drastically. Translocation: A segment from 2 non homologous chromosome gets exchanged. ■ Results in abnormalities as both chromosomes are altered completely. ● Mutations can also change the chromosomal number of a cell, called aneuploidy: ○ Aneuploidy: The presence of an abnormal number of chromosomes in a cell, specifically autosomes. ○ Sex chromosomes can also have an extra chromosome (XXY), resulting in Klinefelter syndrome. ○ A deletion of a sex chromosome can also occur, resulting in Turner syndrome. ● Another way chromosomal mutations can happen is during crossing Over meiosis : ● During meiosis, homologous chromosomes exchange DNA segments through crossing over: ● ● Normal Crossing Over: ○ In a normal exchange, chromosomes line up and swap equal pieces of genetic material. Each chromosome gives and receives an equal chunk. ● Unequal Crossing Over: ○ If the chromosomes don’t align properly, part of one chromosome may be swapped with a much larger or smaller part of the other chromosome. ■ One chromosome might get an extra segment, resulting in gene duplication. ■ The other chromosome might lose that gene entirely because it didn’t receive it during the exchange. ■ Result: One chromosome ends up with two copies of the gene, while the other may have none. ● Translocation: ○ Translocation is another type of chromosomal mutation. ○ It happens when a piece of one chromosome breaks off and moves to a different, non-homologous chromosome (a chromosome that is not its matching pair). ○ This movement can change the order of genes and sometimes mess up how they work, causing mutations. ○ ○ Translocations are Often reciprocal, meaning that two non-homologous chromosomes exchange segments with each other. ● Sometimes in meiosis, the chromosomes do not divide properly ● this is called nondisjunction ○ can cause an egg or sperm cell that has too many or too few chromosomes Impact on Phenotype ■ Chromosome mutations can affect many genes at once, leading to noticeable changes in an organism’s traits. ■ A chromosomal mutation may also break up a gene, making it non-functional. ■ example on how chromosomal mutations affect phenotype: ■ Translocated genes may come under the control of gene promoters when they are moving during translocation, the process where parts of two chromosomes break off and switch places. ■ Promoters are a short stretch of the DNA before a gene, and they act like start signals, telling us when to turn the gene on, or how much of a protein to make from the gene. They also determine how active or inactive the gene is, affecting protein production. ■ When A translocated gene is controlled by a new promoter, it may become overactive or underactive, causing too much or too little protein being made, changing how traits are expressed. ■ This kind of misregulation can sometimes lead to diseases like cancer, especially when genes that control cell growth or division are affected. ■ ■ Impact on Offspring ● Mutations happen in both body and germ cells ● Mutations in body cells only affect the organism in which they occur. \ ● ● Mutations in germ cells may be passed to offspring and influence their traits ● Mutations are the main cause of genetic variation, introducing new changes in DNA sequences that lead to different traits. ● If these mutations are harmful, they may interfere with normal development or even cause death before the offspring can reproduce. ● Some of these harmful mutations are less severe but lead to less adaptive traits (phenotypes), meaning the organism might be less suited to its environment. ● Natural selection removes these harmful mutations from the population over time. ○ Natural selection is the process where organisms with traits that help them survive and reproduce are more likely to pass on their genes. ● ○ Over generations, individuals with harmful mutations are less likely to survive or reproduce, so the harmful mutations gradually disappear from the population. ● Rarely, a mutation results in a beneficial trait (phenotype) that helps the organism survive or reproduce better. ● These beneficial mutations are favored by natural selection and increase in the population over generations. ● ● Mutations are the main cause of genetic variation, introducing new changes in DNA sequences that lead to different traits. Mutations can be caused by several factors ● Organisms have tools to repair mutations ○ However, events and substances can make mutations happen faster than the body’s repair system can handle ● Mutations can also happen naturally . For ex, a small number of replication errors are not fixed by DNAP during replication ○ ● they build up overtime and affect how the cell works Mutagens are agents in the environment that can change DNA ○ they speed up the rate of replication errors and sometimes break DNA strands ○ Some mutagens occur naturally, such as UV rays in sunshine while others are industrial chemicals ● The human body has DNA repair enzymes that help find and fix mutations ○ for ex, Uv light can cause neighboring thymine nucleotides to break their bond with Adenine and bond with each other instead ○ Usually, one enzyme removes the bonded thymines, another replaces the damaged section and bonds the new segment, and the third bonds the new segments in place ■ Sometimes, these enzymes don’t work properly due to mutations in the DNA. ■ Mutations in DNA can damage systems that control the cell’s behavior. ■ These systems regulate gene expression and protein production. ■ When damaged, the cell may not respond properly to signals. ■ For example, mutations can disable cell cycle checkpoints, ● which normally stop the cell from dividing if there’s a problem. ■ If checkpoints are damaged or bypassed, ● the cell may keep dividing even with DNA errors. ■ This can lead to uncontrolled cell growth and eventually cancer. ■ The three smallest types of mutations are: insertion, deletion, and substitution. ■ Interphase occurs only once during meiosis, and crossing over happens in meiosis, not in mitosis. A mutation can affect an organism to different degrees. The effect depends on factors such as the number of genes involved and the location of the mutation. Some cancer drugs take advantage of mutagenic properties by causing similar damage to cancer cells. One type of drug wedges its way between nucleotides, causing so many mutations that cancer cells can no longer function.