Meiosis
Chromosomes (X’somes) chromosomes come in ____
Chromosomes (X’somes) chromosomes come in pairs and humans have __ pairs
Chromosomes (X’somes) chromosomes come in pairs and humans have 23 pairs this means humans have ___ total chromosomes
Chromosomes (X’somes) chromosomes come in pairs and humans have 23 pairs this means humans have 46 total chromosomes
Karyotype all of an organism’s chromosomes, photographed, cut out, and arranged by homologous pairs
Human Karyotype 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 XX (or XY)
Autosome chromosomes that do not genetically determine gender
Human Karyotype 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 XX (or XY)
Sex Chromosome chromosomes that genetically determine gender X and Y
Human Karyotype 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 XX (or XY)
Alleles different versions of the same type of gene Ex: blue eye color vs. brown eye color
Homologous Chromosomes pairs of chromosomes that have the same structure and pair during meiosis
Homologous Chromosomes can carry different alleles cells have two of each chromosome one chromosome in each pair from the mother (maternal), the other from the father (paternal) paternal and maternal chromosomes carry different alleles
Meiosis the process by which gametes (sex cells) are produced from a parent cell
Many plants produce gametes (sex cells) also! Prentice-Hall Biology Fig. 10-3 p.156
Meiosis & Chromosome Number meiosis halves chromosome number
Meiosis & Chromosome Number body (somatic) cells are diploid (2n) have two sets of chromosomes (one maternal and one paternal) n = number of chromosomes in one set = number of chromosomes received from each parent in humans, n = 23
Meiosis & Chromosome Number reproductive cells (gametes) are haploid (n) have only one set of chromosomes (half the diploid number) gametes = sperm & egg
Meiosis & Chromosome Number two consecutive nuclear divisions resulting in four haploid cells Meiosis I and Meiosis II
Discuss the four questions on the left side of your Cornell notes with your table partner.
1. ) Compare & contrast diploid cells (2n) vs. haploid cells (n). 2 1.) Compare & contrast diploid cells (2n) vs. haploid cells (n). 2.) How many divisions occur in meiosis? 3.) How many cells are made? 4.) Are the cells made in meiosis haploid or diploid?
Meiosis I Holt Biology p. 144
Meiosis I chromosome number is halved homologous pairs are separated Each homologue in the cell pairs with its partner, then the partners separate Prentice Hall Biology, p. 158
Meiosis I and Crossing Over Holt Biology p. 144
Crossing Over each chromosome becomes attached to its homologue (partner) all four chromatids are closely aligned nonsister chromatids exchange segments
Effect of Crossing Over after crossing over, each chromosome contains both maternal and paternal segments this creates new allele combinations in offspring
Independent Assortment random distribution of homologous chromosomes
Meiosis 1 and Independent Assortment
Effect of Independent Assortment increases the number of possible different genetic combinations in gametes
Meiosis II the two sister chromatids of each duplicated chromosome are separated from each other two chromosomes (unduplicated) one chromosome (duplicated) p. 158
Meiosis II Holt Biology p. 145
Meiosis Animation
Mitosis Graphic Organizer
Mitosis Graphic Organizer
Meiosis Graphic Organizer
Meiosis Graphic Organizer
Meiosis Graphic Organizer
Meiosis Graphic Organizer
Random Fertilization remember, meiosis produces gametes, a.k.a. sex cells sex cells combine randomly during fertilization to produce a new organism because fertilization of an egg by a sperm is random, this also increases the number of possible genetic combinations
Evolutionary Change crossing over, independent assortment, and random fertilization all increase the number of possible genetic variations more genetic combinations = more possibilities for organisms to evolve
Errors in Meiosis sometimes a gamete can be produced with an incorrect number of chromosomes because of non-disjunction non-disjunction – failure of chromosomes to separate during anaphase I or II of meiosis
Meiosis and Non-disjunction Normal meiosis(A) Failure of homologous chromosomes to separate in anaphase I of meiosis I (B) Failure of sister chromatids to separate in anaphase II of meiosis II (C) A B C
Meiosis and Nondisjunction
Meiosis and Nondisjunction
Errors in Meiosis sometimes a gamete can be produced with an incorrect number of chromosomes because of non-disjunction non-disjunction – failure of chromosomes to separate during anaphase I or II of meiosis creates gametes with an extra or missing chromosome
Other Resources Textbook pages 144 - 149