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Chapter 11-4 Meiosis
Transcript of Chapter 11-4 Meiosis
The Principle of Independent Assortment states that genes segregate according to chance.
(related to the chapter, he made more than just this one) Menel's Principle First, an organism with 2 parents must inherit a single copy of every gene from each parent Second, when that organism produces gametes (sex cell), those two sets of genes must be separated so that each gamete contains just one set of genes chromosomes (strands of DNA and protein inside the cell nucleus) are gene carriers, which are located in specific positions on the chromosomes homologous refers to chromosomes in which one set comes form the male parent and one set from the female a cell that contains both sets of homologous chromosomes is called diploid meaning "two sets" the diploid cells of most adult organisms contain two complete sets of inherited chromosomes and 2 complete sets of genes the diploid number of chromosomes is sometimes represented by the symbol of N2 some cells have only a single set of chromosomes, meaning they also have a single set of genes they are called haploid meaning "one set" gametes of sexually reproducing organisms are haploids including fruit flies the haploid number is 4, written as N=4 a process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell (undergoes a round of chromosome replication during interphase, and each replicated chromosome consists of 2 identical chromatids joined at the center like mitosis) in prophase 1 of meiosis, each replicated chromosome pairs with its corresponding homologous chromosome, the pairing is called tetrad which contains 4 chromatids crossing-over is a process that homologous chromosomes form tetrads first, the chromatids of the chromosomes over one another and then the cross sections of the alleles containing chromatids are exchanged, causing crossing-over therefore to produce new combinations of alleles in the cell Prophase 1 Metaphase 1 Prophase 1 when anaphase 1 is complete, the separated chromosomes cluster at opposite ends of the cell
in telophase 1 a nuclear membrane forms around each cluster of chromosomes
cytokinesis follows, forming the 2 cells Telophase 1 Cytokinesis Meiosis 1 results in 2 daughter cells
because each pair of the two homologous chromosomes was separated, neither of the 2 cells has has the 2 complete sets of chromosomes Conclude Meiosis 1 the chromosomes become visible but do not pair to form tetrads because homologous pairs were already separated Prophase || the final 4 phases of meiosis || are similar to the ones in meiosis |, but result in 4 haploid cells
each daughter cell receive 2 chromosomes and contain the haploid number (N) The last four phases asexual reproduction
daughter cell receives 1 complete set of chromosomes
does not usually change the chromosome number of the original cell, diploid cell enters with 8 chromosomes and will divide into 2 daughter cells with each having 8 chromosomes
is a single cell division, with two genetically identical diploid cells sexual reproduction
homologous chromosomes line up and move to separate daughter cells
chromosome number is reduces in half, a diploid cell enters with 8 chromosomes and will pass through 2 meiotic divisions to make 4 haploid gamete cells, each with 4 chromosomes
meiosis requires 2 rounds of cell division and produces a total of 4 daughter cells in most organisms which are genetically different haploid cells Would they be inherited? Thomas Hunt Morgan ran a experiment in 1910 with fruit flies
after identifying more than 50 fruit fly genes, he noticed they were linked, which violated the principle of independent assortment
he noticed that some genes were inherited and were in 4 linkage groups and 4 pairs of chromosomes in the fruit fly, he concluded that each chromosome is a group of linked genes, and that Mendel's principle of independent assortment was still true
its the chromosomes that assort independently not individual genes
Alleles of different genes tend to be inherited together from one generation to the next when those genes are located on the same chromosome Fun Fact: Human sperm and egg cells have 23 chromosomes each, and when they combine in fertilization, they produce a single cell with 46 chromosomes, or 23 similar pairs. method of identifying and locating genes on chromosomes
by studying the inheritance of trait within a family, scientists can map the gene that controls the trait to a position on a particular chromosome
modern techniques of gene mapping focus on DNA unlike previous methods which used breeding and crossbreeding
today a chromosome's DNA is cut into gene-sized fragments Fact: Each human body has an estimated 20,000 to 30,000 total genes D
E as prophase 1 ends a spindle started to form and attaches to each tetrad
during meaphase 1, paired homologous chromosomes line up across the center of the cell
as the cell moves into anaphase 1, the pairs separate
during anaphase 1, spindle fibers pull each homologous pair toward opposite ends of the cell in male animals, these gametes are called sperm
in some plants, pollen grains have haploid sperm cells
in female animals, there is usually one cell for reproduction called an egg
after fertilization this egg becomes a zygote which undergoes cell division, eventually forming into an organism Article Link: http://ic.galegroup.com/ic/suic/ReferenceDetailsPage/ReferenceDetailsWindow?failOverType=&query=&prodId=SUIC&windowstate=normal&contentModules=&mode=view&displayGroupName=Reference&limiter=&currPage=&disableHighlighting=false&displayGroups=&sortBy=&source=&search_within_results=&action=e&catId=&activityType=&scanId=&documentId=GALE%7CCV2644031394