Text - 169-175

Biozone 1 - pg 115-116, 143-144, 151-152, 145-146, 241-243

Course Pack - 47

Power Points - L1, L2, L2.5

Additional - Karyotyping activity, Crash Course Videos, Meiosis Video

Cell Division

• Cell division is important for cells to receive genetic material to function, to grow, to heal/repair, and to replace dead cells

  • Genetics - The study of heredity and variation of living organisms and how genetic information is passed from one generation to the next

• The cell theory, one of the central ideas in biology, states that:

  • All living things are composed of one or more cells

  • Cells are the smallest units of living organisms

  • New cells come only from pre-existing cells by cell division

    • This turns a parent cell into daughter cells

• All somatic cells go through cell cycles to become two cells

  • Somatic Cell - A plant or animal cell that forms the body of the organism; excludes reproductive cells

The Cell Cycle

• The three main stages of the cell cycle are interphase, mitosis, and cytokinesis

  • {diagram of pie chart}

  • {diagram of all three stages}

• Interphase - The stage of the cell cycle during which a cell carries out its normal functions, grows, and makes copies of its genetic material in preparation for the next stage of the cycle

  • The cell grows, matures, copies its DNA, and prepares for division

  • Growth 1 is the major period of growth where the cell synthesizes many new molecules

  • Synthesis is the period where DNA is replicated as uncondensed fibres called chromatin

  • Growth 2 involves the production of more molecules

• Mitosis - The stage of the cell cycle where a cell’s nucleus and genetic material divide

  • Prophase - The stage where the cell’s chromatin condenses into chromosomes, the nucleus and nucleolus disappear, and spindle fibres form from the centrosomes and move towards the poles

    • Each chromosome exists as two copies of one chromosome called sister chromatids, as they have been replicated in interphase

      • Chromosome - A structure in the nucleus that contains DNA

      • Sister Chromatid - One of two chromosomes that are genetically identical and held together at the centromere

        • Centromere - The region where two sister chromatids are held together in a chromosome

    • Spindle Fibre - A microtubule structure that facilitates the movement of chromosomes within a cell

    • Centrosome - A structure that helps to form the spindle fibres

  • Metaphase - The stage where the spindle fibres from each pole attach to the centromere and guide the chromosome to the equator of the cell

  • Anaphase - The stage where each centromere splits apart, and sister chromatids, now individual chromosomes, are separated to opposite poles so that each pole has a complete set of DNA

  • Telophase - The stage that begins when chromosomes reach the opposite ends of the cell, where chromosomes start to unwind, spindle fibres break down, and the nucleus and nucleolus reform

• Cytokinesis - The stage of the cell cycle that involves the division of the cell cytoplasm and creation of two new daughter cells

  • In animal cells, an indentation forms and deepens as microfilaments constrict until the cell is pinched in two

  • In plant cells, a new cell plate forms between the two daughter nuclei, and cell walls form on either side of the plate

  • In prokaryotic cells, the duplicated DNA is pulled apart, and binary fission separates the cells

  • The daughter cells then begin interphase at G1

• Cell cycle checkpoints monitor cell growth

• Cell growth is monitored by a network of signals

The Structures of Genetic Material

• DNA is made of two long strands that form a spiral shape called a double helix

• DNA is usually in strands of chromatin, until mitosis begins

• The individual units of each strand of DNA are called nucleotides, made of a phosphate group, a sugar group, and a base

  • Sugar and phosphate groups serve as the backbones of the strands

  • The bases protrude inwards, and are paired as either adenine and thymine (A and T) or guanine and cytosine (G and C)

• Genome - The complete DNA sequence of an organism

• To replicate DNA, the double helix is unwound, and the bases on each strand of DNA serves as a template for a new strand, called semi-conservative replication because half of the original DNA is kept

Chromosomes

• Chromosomes are always paired

• In humans, one half comes from each parent, which are paired as homologous chromosomes

  • Sex Chromosome - An X or Y chromosome, which determines the genetic sex of an organism

    • Females have two X chromosomes, and males have an X and an Y

  • Autosome - A chromosome that is not involved in determining the sex of an organism

  • Homologous Chromosome - A chromosome that contains the same sequence of genes as another chromosome

    • They have similar length, centromere location, and banding patterns, but can have different forms genes

    • Gene - A part of a chromosome that governs the expression of a trait and is passed on to offspring; it has a specific DNA sequence

    • Allele - A different form of the same gene

• Karyotype - A photograph of pairs of homologous chromosomes in a cell

  • A sample of chromosomes is stained, sorted, and paired

  • The autosomes are labeled as pairs 1 to 22, and the sex chromosomes are labeled as X or Y

Sexual Reproduction

• Asexual Reproduction - Reproduction that requires only one parent and produces genetically identical offspring

• Sexual Reproduction - Reproduction that requires two parents and produces genetically distinct offspring

  • This involves the fusion of male reproductive cells with a female reproductive cell

  • Gamete - A male or female reproductive cell

  • Zygote - A cell formed by the fusion of two gametes

  • Fertilization - The joining of male and female haploid cells

  • Gametes have half the number of chromosomes than the parent somatic cell

    • Haploid - A cell that contains half the number of chromosomes as the parent cell, represented by n

    • Diploid - A cell that contains pairs of homologous chromosomes, represented by 2n

Meiosis

• Meiosis - The cellular process that produces cells containing half the number of chromosomes as the parent cell (genetic reduction) and are genetically unique through combinations of alleles (genetic recombination)

• Interphase Before Meiosis- Cells that will divide by meiosis will proceed through growth and synthesis, and replicate their chromosomes, so that the meiosis begins with duplicated chromosomes

• Meiosis has two complete cycles

• Prophase I - Each pair of homologous chromosomes line up side by side in synapsis, where genetic information is exchanged through crossing over

• Metaphase I - The pairs of homologous chromosomes line up along the equator of the cell, and spindle fibres attach to the centromere of each homologous chromosome

• Anaphase I - The homologous chromosomes separate and move to opposite poles, which turns a diploid cell into a haploid cell

• Telophase I - Homologous chromosomes begin to uncoil and the spindle fibres disappear, the nuclear membrane forms, and two haploid cells form through cytokinesis

• Prophase II - The nuclear membrane disappears and spindle fibres reappear

• Metaphase II - A haploid number of chromosomes line up at the equator

• Anaphase II - Sister chromatids are pulled apart at the centromere by the spindle fibres towards opposite poles of the cells

• Telophase II - The nuclear membrane and nuclei reform

• Cytokinesis occurs, resulting in four unique haploid cells

• Spermatogenesis - The process of producing male gametes in mammals

  • It begins with a diploid cell called a spermatogonium, which reproduce beginning at puberty by mitosis, and then undergo meiosis

  • Following meiosis II, the cells undergo a final set of developmental stages to develop into four mature sperm

• Oogenesis - The process of producing female gametes in mammals

  • Meiosis takes place in the ovaries

  • It begins with a diploid called an oogonium, which reproduces before birth by mitosis

  • They begin meiosis, but stop at prophase I, where one cell will complete meiosis I every month after puberty

  • This involves an uneven division of cytoplasm, so that the meiosis will form one large, viable egg and a non-viable polar body

  • Once fertilized by sperm, the egg will finish meiosis II and produce one mature egg, and another polar body

  • Twins can be caused by two eggs that are both fertilized, or if a single zygote is divided into two separate bodies

• Meiosis forms genetically distinct haploids through independent assortment and crossing over

  • Independent Assortment - The orientation of each chromosome in a homologous pair to one pole, which can result in a variation of possible gametes containing a combination of maternal and paternal chromosomes

    • The number of genetically distinct gametes can be represented by 2ⁿ

  • Crossing Over - The exchange of chromosomal segments between a pair of homologous chromosomes during prophase I

    • As a result, individual chromosomes contain some genes of maternal origin and some genes of paternal origin

• Errors during meiosis in both independent assortment and crossing over can result in abnormalities of chromosome structure

  • Deletion - A piece of a chromosome is deleted

  • Duplication - A section of a chromosome appears two or more times in a row

  • Inversion - A section of a chromosome is inverted

  • Translocation - A segment of one chromosome becomes attached to a different chromosome

• Errors in chromosome numbers are the result of non-disjunction

  • Non-disjunction - The failure of homologous chromosome pairs or sister chromatids to separate during the anaphase stages in meiosis

    • If it occurs during anaphase I, two gametes will have one extra, and two gametes will have one fewer

    • If it occurs during anaphase II, two games will have the normal amount, one gamete will have one extra, and one gamete will have one fewer

  • Monosomy - The loss of a chromosome as a result of non-disjunction

  • Trisomy - The gain of an extra chromosome as a result of non-disjunction

• Common chromosomal abnormalities in humans

  • Down Syndrome - Trisomy 21, and includes intellectual disabilities and a short stature

  • Edward’s Syndrome - Trisomy 18, and includes intellectual and physical disabilities and facial abnormalities

  • Patau’s Syndrome - Trisomy 13, and includes intellectual and physical disabilities, many organ defects, and a large triangular nose

  • Klinefelter’s Syndrome - XXY, and includes sexual immaturity

  • Jacobs’ Syndrome - XYY, and may be taller than average

  • Metafemale - XXX, and includes menstrual irregularity

  • Turner’s Syndrome - XO, and includes a short stature and underdevelopment sexually

• Prenatal genetic testing involves tests performed on a fetus to test for genetic-based abnormalities

  • This can include maternal blood tests and ultrasounds to provide information about potential physical and chromosomal abnormalities, which are non-invasive

    • Fetal proteins and fetal neck fluids are obtained and tested

  • Invasive procedures include collecting fetal DNA through amniocentesis, the taking a sample of amniotic fluid in the 14th week, or chorionic villus sampling, where cells from the chorion of the placenta are sampled in the 9th week of pregnancy