Chapter 19: Inherited Change

 All living thing reproduce  Asexual reproduction : single organism produces offspring genetically identical to itself. Division by mitosis in eukaryotes and binary fission in prokaryotes  Sexual reproduction : offspring and genetically different than 2 parent organisms Reproduction

 Each parent produces specialized reproductive cells, known as gametes  Gametes fuse together during fertilization to produce the first cell of the new organism, called a zygote Sexual reproduction

 Fusion of gametes requires that chromosome number to be halved at some point (meiosis)  Meiosis occurs as gametes are formed inside the testes and ovaries  Gametes produced from normal diploid (2n) cells resulting in haploid (n) cells  Fusing of two haploid (n) cells results in a single diploid (2n) cell Sexual reproduction

 Meiosis also introduced genetic variation into the gametes and therefore the zygotes that are produced  Genetic variation can also arise by mutation, which can happen at any stage in a life cycle  Genetic variation produces diverse range of species that live on Earth Sexual reproduction

 Involves two divisions: Meiosis I and Meiosis II  Meiosis I: referred to as a reduction division resulting in two cells with half the number of chromosomes as the original cell  Meiosis II: chromosomes behave like mitosis Meiosis

 Chromatid : individual DNA structure. Contains single DNA molecule  Sister chromatids : identical chromatids that make one chromosome  Homologous chromosomes : similar but not identical chromosomes. Each carries the same genes in the same order, but the alleles for each trait may not be the same. In each pair, one chromosome comes from mother and one from father  Centromere : part of a chromosome that links sister chromatids Chapter 5 vocab review

Two events during meiosis help produce genetic variation:  Independent assortment of the homologous chromosomes into 4 resulting cells during anaphase I  Crossing over happens between chromatids of homologous chromosomes Meiosis

 Name the stage of meiosis at which each of the following occurs. (Remember to state if it is division I or division II) a)Homologous chromosomes pair to form bivalents b)Crossing over between chromatids of homologous chromosomes take place c)Homologous chromosomes separate d)Centromeres split and chromatids separate e)Haploid nuclei are first formed SAQ 19.1

a)prophase I b)b) prophase I c) anaphase I d) anaphase II e) telophase I SAQ 19.1

 A cell with three sets of chromosomes is said to be triploid, 3n. A cell with four sets of chromosomes is said to be tetraploid, 4n. Could meiosis take place in a 3n or a 4n cell? Explain your answers SAQ 19.2

 Meiosis could not take place in a triploid, 3n, cell, because there is an odd number of each chromosome, so they will not be able to pair up.  In theory, meiosis can take place in a tetraploid, 4n, cell because there is an even number of each kind of chromosome, so they can each find a partner to pair up with. In practice, meiosis is often very difficult in a 4n cell because, if there are four homologous chromosomes present, they all tend to join up with each other. Crossing over between chromatids of different chromosomes results in an inextricable tangle, so meiosis cannot proceed effectively. SAQ 19.2