Meiosis Mcguire - Meiosis Objectives 10.1.1 – Describe...

Info icon This preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Meiosis Objectives 10.1.1 – Describe Describe the the behavior behavior of of the the chromosomes chromosomes in in the the phases of phases of meiosis. meiosis. 10.1.2 – Outline the formation of chiasmata in in the the process of croscros- sing sing over. over. 10.1.3 – Explain how meiosis meiosis results results in an effectively infinite genetic variety in in gametes through through crossing over over in prophase and random prophase I random orientation in metaphase metaphase I. I. 10.1.4 – State Mendel’s law of of independent independent assortment. assortment. 10.1.5 – Explain the the relationship relationship between Mendel’s law of of independent pendent assortment assortment and and meiosis. meiosis. 4.2.5 – State that, in karyotyping, chromosomes are arranged in pairs pairs according according to their their size and structure. structure. (Review) 4.2.7 – Analyze a human karyotype to determine gender and whether whether non-disjunction non-disjunction has occurred. occurred. (Review) Definition of meiosis (Review) 4.2.1 4.2.1 Meiosis is a reduction division of a diploid (2n) nucleus to form haploid (1n) nuclei. Eukaryotic species have a characteristic number of chromosomes in the nucleus. Human somatic somatic (body) cells have 46 chromosomes. Human gametes gametes (sperm & eggs) eggs) have have 23 chromosomes. Blue & red represent chromosomes from mother & father. Sperm has an uneven mix of red & blue, and some that are combinations. Mitosis vs. meiosis (Review) 4.2.1 Meiosis reduces chromosome number from 2n to 4.2.1 1n. Chromosomes replicate before either mitosis or meiosis. In mitosis 1 cell division produces 2 diploid daughter cells. In meiosis: 2 cell divisions produce 4 haploid daughter cells. Homologous chromosomes (Review) chromosomes 4.2.2 4.2.2 Homologous are chromosome pairs of the same length, centromere position, and staining pattern that possess genes for the same characters at corre-sponding loci. One homologous chromosome is inherited from the father and one from the mother. A set of homologous chromosomes produces a karyotype. Homologous chromosomes (Review) chromosomes 4.2.2 4.2.2 Homologous are chromosome pairs of the same length, centromere position, and staining pattern that possess genes for the same characters at corre-sponding loci. Homologous Homologous pairs pairs of of chromosomes chromosomes Centrome re Process of meiosis Meiosis reduces chromosome number from 2n to 1n. In interphase each chromosome of a pair replicates form-ing two identical sister chromatids joined at centromere. Process of meiosis Meiosis reduces chromosome number from 2n to 1n. In prophase I, pairs of sister chromatids join to form tetrads and exchange segments – called crossing over. Note Note tetrads tetrads in in prophase prophase II made made of of 2 2 pairs pairs of of sister sister chrochromatids, matids, all all 4 4 homologous. homologous. Process of meiosis Meiosis reduces chromosome number from 2n to 1n. In metaphase 1, homologs line up at metaphase plate. They line up randomly, introducing genetic variation. Process of meiosis Meiosis reduces chromosome number from 2n to 1n. In anaphase 1, tetrads split, but sister chromatids remain attached and move to opposite poles of the cell. Process of meiosis Meiosis reduces chromosome number from 2n to 1n. In telophase 1, two cells form and separate, each with a pair of sister chromatids. Nuclei may or may not reappear. Process of meiosis Meiosis reduces chromosome number from 2n to 1n. nd cell division separates After telophase 1, a 2nd the sister chromatids. Each gamete then has only 1 copy of DNA. Formation of chiasmata During prophase 1, the four homologous chromosomes in tetrads are so close together that non-sister chromatids can cross over and fuse. From parent’s Mother Father Crossing over Haploid (1n) gametes Result: Result: no no sperm sperm or or eggs eggs are are identical. identical. Tetrad: the 4 homologous chromosomes One parent’s DNA The crossing (fusion) points within the tetrads are called chiasmata. Formation of chiasmata Crossing over – non-sister chromatids of homologous chromosomes exchange genetic information: the genomes of the mother & father of this parent mix. Result: Result: no no sperm sperm or or eggs eggs are are identical. identical. Chiasmata – the cross over points Genetic variation Crossing over in prophase I, and the random orientation* that occurs in metaphase I, introduce genetic variation (also the random joining of a unique sperm and egg at fertilization). This This is is the the advantage advantage of of sexual sexual reproduction reproduction over over asexual. asexual. *There There are are 23 23 chromochromo- Assort in 2n different ways; n = haploid #. Here 22 = 4. (Metaphase I) some some pairs pairs in in human human germ they germ cells, cells, therefore therefore they can can line line up up in in 23 = 2 ferent 223 = 8,388,608 8,388,608 difdifferent ways. ways. Sperm and > Sperm and egg egg can can produce produce > 64 individuals. 64 trillion trillion unique unique individuals. Genetic variation Mendel’s Law of Independent Assortment: alleles of different genes assort independently of one another during gamete formation. In a dihybrid cross: From From a a parent’s parent’s genotype, genotype, determine determine his/her his/her gametes: gametes: Genetic variation Mendel’s Law of Independent Assortment: alleles of different genes assort independently of one another during gamete formation. (when they are on different chromosomes!) Mendel’s law results from metaphase I of meiosis. Assort in 2n different ways; n = haploid #. Here 22 = 4. (Metaphase I) Non-disjunction (Review) 4.2.4 4.2.4 Non-disjunction: an accident of meiosis or mitosis in which the members of a pair of homologous chromosomes or sister chromatids fail to move apart properly. Some gametes get 2 of one chromosome; others get get none. Ex: Down syndrome (trisomy 21) Non-disjunction (Rev.) Down syndrome (trisomy 21) 3 copies of chromosome 21 The The karyotype karyotype Karyotyping (Review) 4.2.5 4.2.5 In karyotyping, chromosomes are arranged in pairs according to their size and structure. A picture of one’s chromosomes Karyotyping (Review) 4.2.6 4.2.6 Karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities. The The chorion chorion is is aa membrane membrane forming forming the the placenta. placenta. Karyotyping (Review) 4.2.6 Social and 4.2.6 ethical issues of karyotyping unborn fetuses Abortion of fetuses with abnormalities Abortion based on gender or superficial characteristics Eye color? Karyotyping (Review) 4.2.7 4.2.7 Analyze a human karyotype to determine gender and whether non-disjunction has occurred. What is the sex? Karyotyping (Review) 4.2.7 4.2.7 Analyze a human karyotype to determine gender and whether non-disjunction has occurred. XYY XYY syndrome syndrome -- Affected Affected individuals individuals are are usually usually very very tall tall and and thin. thin. Many Many experience experience severe severe acne acne during during adolescence. adolescence. Additional Additional symptoms symptoms may may include include antisocial antisocial or or behavioral behavioral problems problems and and learning learning disabilities. disabilities. Intelligence Intelligence is is usually usually normal, normal, although although IQ, IQ, on on average, average, is is 10 10 to to 15 15 points points lower lower than than siblings. siblings. Karyotyping (Review) 4.2.7 4.2.7 Analyze a human karyotype to determine gender and whether non-disjunction has occurred. Trisomy 18 18 is a disorder that shows symptoms symptoms as as soon as the child is born. About 25% of Edward's Edward's syndrome victims die before before they are are one one month month old, old, and only 10% live for one year....
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern