Biology quiz #2 practise

• • Cell division that produces sex cells (sperm and egg cells)
• • End result are cells with half the chromosomes (in humans, n = 23)
• • Occurs in the gonads (ovaries and testes)
• Half the chromosomes are needed to ensure correct number of chromosomes after fertilization
• Two divisions are needed
• Daughter cells are genetically different
• females enter meiosis I during the fetal stages. Once puberty begins, one germ cell each month enters meiosis II to produce an egg.
• Males do not begin any stage of meiosis until puberty.
• During Interphase I the chromosomes duplicate
• During Prophase I The Homologous chromosomes pair and exchange segments (crossing over)
• synapsis- pairing of homologs to form tetrad
• During Metaphase 1 The tetrads line up in pairs at the metaphase plate of the cell
• During Anaphase I Pairs of Homologous Chromosomes split up

  The chromosomes' sister chromatids do not separate as they do in mitosis.
• during telophase, As in mitosis, the chromosomes arrive at opposite ends of the cell, and new nuclear membranes form.
• End of cytokinesis 1

  The rest of the cell divides.Cytokinesis, the division of the cell's cytoplasm, is now complete.
• Interphase IIThe chromosomes do not replicate during this phase, as they do in interphase in mitosis and interphase I in meiosis.
• Prometaphase IIThe spindle fibers attach to the chromosomes. The centrioles are now at opposite ends of the cell.As in mitosis prometaphase, fibers from both ends of the cells attach to each one of the four chromosomes.
• Prophase IIAs in prophase I, the chromosomes condense, spindles form, the centrioles begin to separate, and the nuclear membrane fragments and disperses.Unlike prophase I, the chromosomes do not attach to the nuclear membrane in order to exchange genetic information.
• Metaphase IIThe chromosomes align along the metaphase plate.As in mitosis metaphase, (and unlike meiosis metaphase I), fibers from the centrioles begin to pull on each one of the chromosomes from both directions.
• Anaphase IIAs in anaphase in mitosis (and unlike anaphase I in meiosis), the fibers pull the chromatids apart and toward opposite ends of the cells.
• Telophase IIThe chromatids arrive at the either end of each cell and new nuclear membranes form
• End of cytokinesis 2The rest of the cell continues to divide. Only when two, distinct cells form will cytokinesis, the division of the cell's cytoplasm, be complete.There are now four daughter cells. Each cell has one set of chromosomes, or one half the number of the initial cell.
•  Gamete

  A sex cell → sperm in males, eggs in females
•  Fertilization

  Joining two gametes to form a zygote
•  Zygote

  Cell produced from the fusion of 2 gametes
•  Tetrad

  A pair of homologous chromosomes, each with two sister chromatids
•  Synapsis

  The pairing up of homologous chromosomes
•  Crossing over

  Exchange of chromosome segments (DNA) between homologous pairs during synapsis
• Humans have 46 chromosomes consisting of 23 pairs

  Each pair consists of two homologous chromosomes

  • Similar in size, shape and genetic compound
  • Each homologue comes from each parent (one from the biological mom and one from the biological dad)
• Locus: where (location) a gene is found on a chromosome (loci → plural)
• • Allele the form that a gene can come in

  Ex. gene for eye colour, alleles for blue and brown eyes
• Somatic Cells

  • Any cell except for sperm and egg cells (any other body cells)
  • Contain 46 chromosomes
  • 2 sets of 23 chromosomes
• Reproductive Cell

  • Egg cells and sperm cells (sex cells)
  • Contain 23 chromosomes
  • 1 set of 23 chromosomes
• Diploid Cells

  • Contain 2 sets of chromosomes
  • Denoted as 2n = 46 (in humans)
  • Somatic cells are diploid cells
• Haploid Cells

  • Contains one set of chromosomes
  • Sex cells are haploid cells
  • Denoted as n = 23 (in humans)
  • because this way when fertilization occurs, it will form one full diploid cell 23+23=46=diploid
• Fertilization

  The formation of a zygote, by the joining together, or fusion, of two gametes
• DNA

  • Short for deoxyribonucleic acid
  • Is a type of nucleic acid (complex organic substance that holds information)
  • Found in the nucleus and is the main component of genes
• Dna is

  • Made up of three smaller building blocks

  1. Deoxyribose sugar
  2. Phosphate group
  3. Nitrogenous base

  Together these form a nucleotide
• Nitrogenous Bases

  • There are 4 nitrogenous bases in DNA:

  1. Adenine
  2. Guanine
  3. Cytosine
  4. Thymine

  Because of their structures: Thymine always pairs with Adenine, and Guanine always pairs with Cytosine
• Double-Helix

  • DNA is a double chain in the form of a double helix
  • The order of the bases determines the individuality of the nucleic acid