* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Homologous chromosomes
Survey
Document related concepts
History of genetic engineering wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Genomic imprinting wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Designer baby wikipedia , lookup
Microevolution wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Genome (book) wikipedia , lookup
Y chromosome wikipedia , lookup
X-inactivation wikipedia , lookup
Transcript
Welcome Back! Wednesday, November 30th. Bellwork: You have two types of cells in your body: somatic cells, and germ cells. Somatic cells are your body cells. They undergo mitosis when they need to divide. Germ cells are your reproductive cells also referred to as gametes. male gametes are called sperm cells female gametes are called egg cells. Sexual reproduction involves the fusion of two gametes that results in offspring that are a genetic mixture of both parents. 1 Gametogenesis the production of gametes. Sperm cells (male gamete) smaller than female gamete contribution to the embryo is DNA must be able to swim, modifications are made to the cell for this to happen. Egg cells (female gamete) gives DNA, contributes organelles, molecular building blocks, and other materials for a successful embryo to develop Fertilization the actual fusion of two gametes. Occurs when the sperm fertilizes the egg. A zygote is formed that will have the number of chromosomes in a diploid cell. Develops by mitosis into a multicellular organism. Diploid a cell with 2 copies of each chromosome, (2n) number of chromosomes, body cells are diploid. one from female parent one from male parent Haploid gametes that contain only one of each kind of chromosome (n) number of chromosomes. 2 Each organism has a specific amount of chromosomes in their cells. The number of chromosomes is not related to the complexity of an organism. Examples: Adder's Tongue Fern 1260(2n) 630(n) Fruit Fly 8(2n) 4(n) Humans 46(2n) 23(n) Autosomes chromosomes that contain genes for characteristics not directly related to the sex of an organism. Chromosome pairs 122 are autosomes Sex Chromosomes ones that control the development of sexual characteristics. Very different from one another. X and Y are standard XX indicates female, XY indicates male 23 chromosomes All other human cells have 46 chromosomes. If cells only reproduced through mitosis then when an egg cell and a sperm cell fuse, the new cell would have 92 chromosomes! Meiosis is the type of cell division that produces gametes with half the number of chromosomes as a parent's body cells. Two separate divisions occur (Meiosis I and II) Begins with 1 diploid (2n) cell, and results in 4 haploid (n) cells. 3 Homologous chromosomes two chromosomes (one from mom and one from dad) that have the same length and same general appearance. contain the same genes in the same order. Can you identify Homologous Chromosomes? The diagram below shows chromosomes 1 with four different genes present. These genes are represented by the letters F, g, h, and J. Possible homologous chromosomes of chromosome 1 are labeled 2 5. Examine the five chromosomes and the genes they contain to determine which of chromosomes 25 are homologous with chromosome 1. 4 1. Could chromosome 2 be homologous with chromosome 1? Explain. yes, because the genes are in the same location and position 2. Could chromosomes 4 be homologous with chromosome 1? Explain. no, because the last gene is not the same 3. Could chromsome 4 be homologous with chromosome 1? Explain. no, because they have completely different genes 4. Could chromosome 5 be homologous with chromosome 1? Explain yes, same as #1 Review Mitosis: 5 Prophase I DNA coils into chromosomes Spindle fibers form Nuclear membrane breaks down Centrioles move to opposite sides of the cell. Crossing over occurs here. Homologous chromosomes line up gene to gene in a fourpart structure called a tetrad. Tetrad is made up of 2 homologous chromosomes, with 2 sister chromatids. Sex chromosomes also pair up with one another 6 Crossing Over The exchange of chromosome segments between homologous chromosomes during prophase I of meiosis. Exchange of genetic material creates more genetic diversity. Results in a new combination of alleles, called genetic recombination. Can occur at any location on a chromosome and in several locations at the same time. Draw a detailed picture using colored pencils to show crossing over occuring. pg 190 In humans approximately 23 crossovers for each pair of homologous chromosomes. Linked Genes or (genetic linkage) genes that are close together on the same chromosome are more likely to be inherited together (linked together) the farther apart two genes are located, the more likely they are to be separated when crossing over. 7 Metaphase I Centromere attaches to spindle fibers Homologous chromosomes are lined up side by side in the middle as tetrads. **Remember: In mitosis they were a single file line** 8 Anaphase I: Homologous chromosomes separate and move to opposite ends of the cell. Centromere does NOT split, sister chromatids stay together. Ensures that each new cell will only have 1 chromosome from each homologous pair. Telophase I: Nuclear membrane forms again. Spindle fibers break down Cytoplasm divides We end up with 2 cells with a unique combination of 23 duplicated chromosomes coming from both parents. Note: Still contains doubled chromosomes. Therefore, a second cell division is necessary to separate the doubled chromsomes 9 Meiosis II: Exactly like mitosis. It divides sister chromatids resulting in undoubled chromosomes. The process described below relates to both cells. Note: DNA is NOT copied again between the two stages. Directions: Use pages 174175 to describe what occurs during each phase and complete a detailed picture of each stage. Prophase II The nuclear membrane breaks down Centrioles move to opposite sides of the cell. Spindle fibers form 10 Metaphase II Spindle fibers align the 23 chromosomes at the cell equator (in the middle). Anaphase II Sister chromatids are pulled apart from each other and move to opposite sides of the cell. Telophase II: Nuclear membranes form around each set of chromosomes at opposite ends of the cell. Spindle fibers break apart. cell undergoes cytokinesis END RESULT OF MEIOSIS Four haploid cells with a combination of chromosomes from mom and dad. Haploid cells become gametes transferring the genes they contain to the offspring. 11 12 13