Sexual Reproduction and Meiosis Chapter 9 PDF

Sexual Reproduction and Meiosis Chapter 9  Why sexual reproduction? Asexual reproduction is easy and simple. Makes identical organisms (Save for some mutations) Found in all prokaryotes, unicellular eukaryotes, and some multi-cell...

Sexual Reproduction and Meiosis Chapter 9  Why sexual reproduction? Asexual reproduction is easy and simple. Makes identical organisms (Save for some mutations) Found in all prokaryotes, unicellular eukaryotes, and some multi-cellular eukaryotes. Sexual Reproduction requires two parents. Each parent makes a sperm or an ova (egg) Conjugation was a precursor to sexual reproduction. Two bacteria exchanging genes with one another. Doesn’t result in reproduction, but more genetic diversity  Sexual reproduction has costs 1 Sexual reproduction requires energy spent to attract mates. Frogs expend energy to produce sound to attract mates. Bluefooted (1) Boobies dance an elaborate courtship 2 ritual. animals Some (2) have to exert a lot of energy to find their mates. The angler fish is one where the male just swims till it finds a female, then it attaches itself to the 3 female and becomes Regardless, absorbed by thean finding female delivering individual his packet to mate of with requires sperm. energy being(3)expended, that asexual organisms do not have  Sexual Reproduction benefits Despite the costs of sexual Yes, what you are thinking is reproduction it has to have benefits, a benefit. It benefits us, because it has been occurring for at because it builds social least 1.5 billion years ago and is bonds, but this is just about successful for a lot organisms, the genetic benefits of sexual reproduction. including most multicellular eukaryotic Sexual reproduction leads to more organisms. genetic diversity. Asexual organisms depend upon mutation as their sole source of genetic diversity. Sexual organisms mix their genes and DNA up with another organism creating unique genomes. Fig. 9.2  Two pair of Chromosomes for every cell. A chromosome is a linear strand of DNA which contains multiple genes. The amount of chromosomes in a cell’s You know some nucleus varies based upon species. organisms are haploid as adult and some are Ploidy means the amount of complete set of polyploid. Polyploid chromosomes a cell contains. means they have Most eukaryotic cells are diploid many sets. Two sets of chromosomes di = two Sperm and egg are haploid One set of chromosomes Humans have two sets of 23 chromosomes per cell. One set from mom (23 from her ova) One set from dad (23 from his sperm)  Diploid cells In diploid cells chromosomes exist in pairs called a homologous pair. Homologous pairs are chromosomes which share the same genes. Or in other words are matching chromosomes. The genes may vary in the These three people all have genes protein building instructions. for hair color on the same For example, we have genes chromosomes, but because they for eye color, but not everyone have different alleles, they have has the same eye color. different results for their hair color. Variations in a gene (which leads to different eye colors, hair colors, etc.) are called alleles.  Karyotype A karyotype is a way of picturing the chromosomes of a particular organism. In humans the chromosomes all have numbers except for the last pair which are 22 pairs of chromosome designated x or y. are designated autosomes. These chromosome are found in all genders and code for proteins not involved with gender identity or sex organs. The last pair of chromosomes are called sex chromosomes and have genes involved with sex identity. In humans typically the genes on the X chromosome lead to a more female development while an individual with a y chromosome will typically develop male.  Meiosis is preparatory for Sexual Reproduction Meiosis involves the splitting of the DNA from one cell, ultimately into four haploid cells. The four haploid cells are called gametes Female gametes are ova (egg) Male gametes are sperm I am the result of The cell goes through a cell division after the fusion of the which the two cells which resulted from sperm of my dad the first cell division each go through with the egg of my their own cell division. Resulting in four mom. cells. Fertilization results in the formation of a zygote from the fusing of an ova with a sperm cell. A zygote will then begin divisions of mitosis to grow and develop into the adult form of the organism.  Specialized Cells go through Meiosis Somatic cells are involved with body growth and cell replacement throughout the life of a multicellular organism. Germ cells are specialized cells which go through meiosis and produces gametes. Animals and plants have different reproductive structures, but they have the same kind of cells. Amphibians, such as frogs, still Most animals produce their exhibit some of their fish ancestry gametes (also known as sex in they have to reproduce in cells) the same way and aquatic environments. reproduce the same. Fig. 9.5  Meiosis a powerful tool of increasing genetic diversity Meiosis cuts the number of chromosomes in half, from diploid (2n) to hapolid (n). Meiosis also mixes the alleles up between homologous pairs of chromosomes. Mitosis results Meiosis goes in a parent through two cell cell (2n or divisions. The diploid) first cell division producing splits up the (2n) daughter homologous cells. chromosomes from one another. The second cell division separates the sister chromatids from each other. The  Meiosis Metaphase of mitosis lines up all the chromosomes so their sister chromatids can be begins… Metaphase of mitosis separated. Metaphase 1 of Meiosis sets it up so the duplicated homologous may be …the same way as mitosis. It begins separated and Metaphase 2 separates with interphase. the sister chromatids S phase is when DNA is Metaphase I of Meiosis through a IIsecond Metaphase cell of Meiosis division. replicated G2 phase is when the proteins are made for cell replication. DNA only replicates once, but two cell divisions are to follow. Meiosis is similar in that they similar named phases of development, but split up into two rounds. Meiosis I Prophase I, Metaphase I, Anaphase I, and Telophase I Separation of the homologous chromosomes Meiosis II Prophase II, Metaphase II, Anaphase II, and Telophase II Separation of the sister chromatids.  First round of cell nucleus division and cell division Prophase I is the most time consuming Duplicated phase of meiosis. Chromosomes The spindle fibers begin to form and The two attach to the kinetochores of the duplicated duplicated chromosomes. homologous What is different is the homologous chromosomes chromosomes come together in what are joined in is called synapsis. synapsis. Crossing over between homologous chromosomes occurs as well. The homologous chromosomes can exchange DNA with one another creating more genetic diversity. A later slide will go into more detail.  Metaphase I and Anaphase I Anaphase I results in the Metaphase I results in the homologous chromosomes homologous chromosomes being pulled apart. lining up together along Note there sister chromatids the cell’s equator. are still attached to one another at the centromere.  Telophase I & Cytokinesis Telophase I results from the complete separation of the homologous chromosomes. Nuclear envelopes reform The two around the separated cells are chromosomes. the Spindle fibers dismantle result of The cell is divided into two the first cells. round of The two cells are now meiosis. haploid. They have half the chromosomes of the original cell. If it was a human cell then it would typically have 23 duplicated chromosomes (sister  Prophase II Prophase II is similar to Prophase of Mitosis. Occurs in the two daughter cells produced at the end of Meiosis I Spindle Fibers reform and connect to the kinetochores of the duplicated chromosomes. Nuclear envelope begins to dismantle and before the end of prophase II the nuclear envelope is non-existent.  Metaphase II & Anaphase II In Metaphase II the chromosomes line up along the cell’s equator. They are lined up to split the sister chromatids Anaphase II the sister chromatids are pulled apart. The kinetochore moves the sister chromatids along the spindles.  Telophase II & Cytokinesis II Original Cell before meiosis Telophase II commences once the chromatids have stopped moving. Nucleus reforms Spindle Fibers dismantle Chromosomes decondense Cytokinesis concludes once 4 cells are produced The four cells are haploid and unique. 4 haploid cells at the end of meiosis. Note that each of the cells are unique and they each have half the DNA of the parent cell.  Meiosis Generates Diversity Crossing over results in recombinant chromosomes. The DNA is exchanged between homologous chromosomes. Results in new combinations of DNA In the picture to the right, the genetics between the red and blue chromosomes have exchanged DNA creating 4 unique chromatids. The homologous chromosomes align separately from each other.  Random Fertilization That means that your parents each had 1 in a 70 trillion chance of being born. The chances that both of your Fertilization is the result of one parents were born is 1 in 4.9 x 1027. sperm meeting with one egg cell. It is remarkable that you were born, There are 8,388,608 different but even more remarkable that both of your parents were born, let alone sperm cells a male can donate. that they met. Chances of any There are 8,388,608 different particular person being born is egg cells the female can donate astronomically low, but the chances Though the females eggs of someone being born is high. We generally like sex. are created at birth and are fewer than 8,388,608, the number given is the amount of egg cells capable of being That meansproduced. every couple has 70 trillion individuals they are capable of producing.  Mitosis and Meiosis Overview Mitosis Meiosis Occurs in somatic cells Occurs in germ cells Homologous Homologous chromosomes line chromosomes don’t up together to be split apart align together. from one another Mitosis splits the sister After first cell division the sister chromatids from one chromatids are separated from another. one another Yields identical cells Yields unique cells One cell division after Two rounds of cell division, but the DNA is replicated only one time DNA is replicated 2 diploid daughter cells. 4 haploid daughter cells  Polyploidy Poly = many Ploidy = means the amount of complete set of chromosomes a cell contains. Polyploidy means many (more than 2) sets of chromosomes. Triploid means 3 sets Tetraploid means 4 Etc. When a germ cell fails to separate the Strawberries are octoploids (8 sets of DNA). The main reason why we use homologous chromosomes in the first them in our DNA extraction lab. The round of cell division, then a diploid other reason is they smell good. gamete maybe produced. Did someone Animals don’t do well with more than 2 say strawberries!! sets of DNA (diploid), but some angiosperms (flowering plants) are capable of producing functional polyploidy cells. Cells with more than a diploid set of chromosomes.  Nondisjunction Nondisunction is the result of one pair of homologous chromosomes failing to split. Results in gametes either missing a chromosome or gaining an extra chromosome. Most embryos with incorrect chromosome numbers cease development and terminate before birth. Trisomy 21 is the result of They account for 50% of the nondisjunction of chromosome Extra miscarriages chromosomes create less 21 and is the frequent cause problems than missing of Downs Syndrome. chromosomes.  Extra or Missing Sex Chromosomes Everyone is Normally females have an XX sex beautiful. I know chromosome allotment and males have it is cheesy, but it an Xy chromosome allotment is true!! Nondisjunction of sex chromosomes can result in a variety of different affects. XXX is called Triplo-X XYY Jacobs Syndrome Tallness, menstrual Generally very normal irregularities, normal IQ Maybe tall May produce some eggs with two X chromosomes. XXY is called Klinefelters X Turner Syndrome Sexually underdeveloped. Short and sexually Large hands and feet and long underdeveloped limbs Infertile, yet hormone May develop breast tissue supplements may promote growth and Y chromosomes always terminate in utero sexual development.  Small Scale Chromosome Abnormalities Deletion = The loss of one or more genes in a chromosome Cri du syndrome is the result of the deletion of several genes Children cry like cats Severe mental retardation and developmental delays. plication results in repeats in the parts of a chromosome. Fragile X syndrome is the result of repeating of a CGG sequence on the X chrom Results in mental retardation The severity of the effect is the result of how many replicates there are pres Can range form 10 to 200 Duplication of genes is a powerful tool for evolution Two genes allows for one gene to change without affecting normal metabolism. An example is a gene used to secrete calcium in tooth enamel of vertebrates duplicated and the duplicate (or the original no way to tell) changed into the gene which produces calcium rich breast milk.  Translocation Translocation is the result of nonhomologous chromosomes exchanging DNA with one another. 95% of people with chronic myelogenous leukemia have part of chromosome 9 translocate to chromosome 22. There are generally no problems if no genes are broken If the translocation takes part of a gene and attaches it to another chromosome, then the full gene is no longer functional. This often has a more drastic affect on the organism.  Gametes The end result of meiosis is four gametes. In humans the gametes of males form in testes and the females in Males produce 4 sperm cells ovaries. If the species is generally monogamous in nature then fewer sperm are produced for a single Gibbons by nature are monogamous. copulation event and most of the sperm is functional If the species is normally promiscuous then males produce more sperm and some of the sperm is dysfunctional Dysfunctional sperm block the Femalespassage ofproduce generally another 1males sperm. ova and 3 polar bodies Polar bodies are typically wasted cells. Chimpanzees are promiscuous. Females put a large investment in one of