Chapter 7 Reproduction & Meiosis PDF

Chapter 7 Part 1  Compare and contrast sexual and asexual reproduction  Asexual reproduction  Sexual reproduction  Diploid life cycle  All living organisms reproduce, how they achieve this can differ. Asexual Reproduction: Sexual Reproduction: Produces identica...

Chapter 7 Part 1  Compare and contrast sexual and asexual reproduction  Asexual reproduction  Sexual reproduction  Diploid life cycle  All living organisms reproduce, how they achieve this can differ. Asexual Reproduction: Sexual Reproduction: Produces identical offspring (clones) Produces variable offspring  A generation of offspring produced by a single individual  Offspring genetically identical to parent and siblings  This type of reproduction can be achieved by various methods:  Binary Fission  Mitosis Advantages How do they introduce genetic variation/diversity?  Budding  Cloning  Vegetative Propagation  Parenthogenesis Disadvantages  And more…  Advantages  Meiosis + fertilization Disadvantages 1. Meiosis = production of haploid cells 2. Fertilization = fusion of haploid cells from two parents to form a single, unique diploid cell  New cell undergoes mitotic cell division to grow into an adult organism  Evolutionary success?  Most eukaryotes reproduce sexually  Multicellular organisms that reproduce asexually are exceedingly rare!  Only mode of reproduction for many How do they introduce animals genetic variation/diversity? Haploid Animals  Rare!  Limited to invertebrate animals  Examples:  Male bees  Wasps  Ants Polyploidy in Animals  Common in plants  Rare in animals  Two species of birds  One mammal:  South American red viscacha rat  Slightly more common in:  Insects  Crustaceans  Fish  Reptiles  Amphibians  Some species of salamanders, frogs and leeches Part 2  Compare and contrast mitosis & meiosis  Describe the stages of meiosis and the important events that occur at each stage  Including the movement of chromosomes  ___________________ Prophase Prometaphase ___________________ Metaphase Mitotic Phase ___________________ Anaphase Telophase ___________________ 2n G2 Cytokinesis 2n S G1 2n G0 Interphase Label the ploidy the of cells produced Label the diagram by mitotic cell of the cell cycle division  1n 1n Meiosis 1 & 2 1n=23 1n Cytokinesis 23 are sister chromatids G2 2n Meiosis I Meiosis II Separation of homologous Separation of chromosomes sister chromatids S 1n G1 1n 1n=23 1n Label the diagram Label the ploidy the of of the cell cycle cells during meiosis 1n=23 Mitosis Meiosis  Involves one cell division  Involves two cell divisions  Produces two diploid (2n) somatic  Produces four haploid (1n) gametes cells that are genetically identical that are genetically unique Steps resemble mitosis, EXCEPT: Two rounds of cell division!  Meiosis preceded Label the parts of the chromosome: by normal interphase Mitotic G1 Spindle S 3 3 Fibers G2 1 Centromeres Chromosome replication in S (tetrad) 2 phase makes 1 2 identical sister Kineto- chromatids Diploid chores 2n=6 All chromosomes are duplicated Sister Chromatids Each consists of 2 identical sister chromatids  Most animals are diploid (2n)  2 sets of chromosomes  1 set from each parent  Meiosis  Results in reduction of chromosome #  Produces haploid (1n) gametes  1 single set of chromosomes  Chromosomes begin to condense AND PAIR UP!  Each chromosome carefully aligns with its homologous partner so that they match at corresponding positions along the length of the chromosome  Homologous chromosomes exchange part of their DNA in a process called crossing over 1. Homologous chromosomes pair-up 2. Synaptonemal complex holds them together in synapsis (physical connection of two chromosomes) 3. Segments of chromosomes exchanged through crossing over  Results in the exchange of genetic information  Produces recombinant chromosomes (chromosomes that carry genes derived from two parents) Visible structures at crossing over points are called chiasmata Note: chromosomes are actually on top of each other as shown above, but to help show crossing over are shown side by side here  Chiasmata sister chromatids Spindle 1. During which step in meiosis does Fibers crossing over occur? 2. Label the structures 3. Is this a diploid or haploid cell? Nuclear Envelope Centrioles centrosome 4.How many homologous chromosomes would a diploid cell have? Tetrad (pair of homologous chromosomes)  Spindle fiber microtubules attach to the kinetochore proteins at the centromeres  Homologous chromosomes still held together at chiasmata  Nuclear membrane completely broken down  Spindles attached to chromosomes  Chromosomes line up in the center of the cell along the metaphase plate Notice: chromosomes “assort independently” along the metaphase plate (i.e. line up randomly!)  Independent Assortment:  Homologous pairs of chromosomes line up randomly at the metaphase plate during metaphase I  Assort themselves without regard to any other chromosomes pair  Homologous chromosomes (genes/alleles) will separate during meiosis without influence from another chromosome (gene/allele)  Key Maternal set of chromosomes Possibility 1 Possibility 2 Paternal set of chromosomes Two equally probable arrangements of chromosomes at metaphase I Metaphase II Each pair of homologous chromosomes is sorted into Daughter daughter cells cells independently of the other pairs Combination 1 Combination 2 Combination 3 Combination 4  Microtubules pull tetrads apart  Homologous pairs move toward opposite poles of the cell  Tetrads separate  Chiasmata are broken but sister chromatids remain attached at the centromeres  Separated chromosomes arrive at opposite poles  Nuclear membrane sometimes reforms and the chromosomes de-condense  (depends on the organism) Result: two haploid daughter cells!  Division of the sister chromatids  Process is basically the same as mitotic division  EXCEPT:  Sister chromatids are NOT genetically identical  Results in daughter cells that are haploid and genetically different  MITOSIS MEIOSIS Parent cell (before chromosome replication) Chiasma (site of crossing over) MEIOSIS I Prophase Prophase I Chromosome Chromosome replication replication Tetrad formed by Duplicated chromosome 2n = 6 synapsis of homologous chromosomes (two sister chromatids) Chromosomes Tetrads positioned at the positioned at the Metaphase I Metaphase metaphase plate metaphase plate Anaphase Sister chromatids Homologues separate during separate Anaphase I Telophase anaphase during Telophase I anaphase I; sister Haploid chromatids Daughter n=3 remain together cells of meiosis I 2n 2n Daughter cells MEIOSIS II of mitosis n n n n Daughter cells of meiosis II Sister chromatids separate during anaphase II Part 3  Explain nondisjunction and how it leads to chromosome abnormalities  Explain errors in chromosome structure through duplication, deletion and structural rearrangements   Karyotype is the number and What happens when appearance of chromosomes, including chromosomes don’t  Length behave properly?  Banding pattern  Centromere position  ____________________________  Cytogeneticists obtain a microscopy image of an individuals chromosomes then cut and paste each into a chart  ____________________________  Even small regions of chromosomes contains many genes  Chromosome disorders typically severe and often fatal Nondisjunction  Occurs when pairs of homologous chromosomes or sister chromatids fail to separate during meiosis  Results in:  duplication of chromosomes  loss of entire chromosomes  changes in entire number of complete sets up chromosomes Nondisjunction Example: Trisomy 21  Euploid  Individual with appropriate number of chromosomes  Aneuploid  Individual with an error in chromosome number  Includes:  Monosomy = loss of one chromosome  Lethal for all autosomes  Trisomy = gain of an extra chromsosome  Most are lethal  Characteristics: Taller-than average height Normal sexual development Slightly smaller head Skeletal abnormalities Mild learning difficulties Attentive deficit Emotional challenges Delayed dev. of motor skills Triple-X Syndrome Seizures Kidney abnormalities  Female (XXX)  ~1 in 1000 births  Up to 90% undiagnosed  Usually mild due to X silencing  Stable hormone treatment can improve symptoms Turner’s Syndrome  Female (X-), typically infertile  ~1 in 2500 births  Much more severe than XXX  Significant heart and kidney issues  Growth hormone and estrogen therapy can improve symptoms Jacob’s Syndrome  Male (XYY),  ~1 in 1000 males affected  Can be diagnosed along with autism Usually taller/stockier  Symptoms include attention difficulties, Prone to acne and skin irritation delayed motor skills and speech, involuntary muscle movement, an Motor ticks emotional or behavioral issues Learning disabilities *Antisocial/aggressive behavioral issues  “Super Man” – some studies have shown up to a 40% increase in incarcerated men – again, highly controversial! Kleinfelter (XXY) Syndrome  Male (XXY) (may be more than two X’s)  Usually infertile  Most common cause of hypogonadism, a condition that stops the body from producing testosterone and sperm  as many as 75% go undiagnosed, usually until seeking medical advice for infertility or loss of sex drive  Can be treated (not cured) with testosterone therapy  Why are extra autosomes more deleterious than extra X chromosomes? Duplications Deletions  Example:  Examples:  Potocki-Lupski syndrome  Cri-du-chat  Extra copy of a small piece of  Deletion of most of small arm of chromosome 17 chromosome 5  Williams syndrome  Deletion of 25-27 genes on chromosome 7  13q deletion  15q deletion Inversions Translocations  Detachment, 180% rotation, and  A segment of chromosome breaks off and reinsertion of a part of a chromosome reattaches to a different, non- homologous chromosome  Change orientation of genes so  Affects vary greatly! typically very mild  Can be benign or devastating  Unless a gene is disrupted  Reciprocal/Robertsonian translocations  Exchange of pieces of chromosome between two non-homologous chromosomes with no loss or gain of genetic information