Grade 11 Bio

UNIT 1: DNA, Chromosomes, Genes & Traits

Vocabulary

  • Chromatid: One of the 2 identical halves of a chromosome (copies of the same chromosome).

  • Chromatin: Material composed of protein, RNA, and DNA (unraveled DNA), forming chromosomes in non-bacterial organisms.

  • DNA: A self-replicating material present in nearly all living organisms, the main constituent of chromosomes and the carrier of genetic information.

  • Gene: A unit of heredity transferred from parent to offspring, which determines some characteristics; a segment of DNA that codes for a specific outcome.

  • Allele: Different versions of a gene (e.g., the eye color gene has alleles for brown, blue, and green eyes).

  • Homologous chromosomes: A pair of chromosomes (one from each parent) that are the same size/shape and contain the same genes.

  • Centromere: The region of a chromosome where microtubules of the spindle attach during cell division.

  • Chromosomes: Threadlike structures of nucleic acids and proteins found in the nucleus of most living cells, containing genetic information.

  • Sister Chromatid: Identical copies formed by DNA replication of a chromosome, joined together by a common centromere.

  • Centriole: A cylindrical organelle near the nucleus in animal cells, involved in the development of spindle fibers.

  • Spindle Fibers: Protein structures that divide genetic material in a cell.

  • Cytokinesis: The process of cytoplasmic division of a cell at the end of mitosis or meiosis.

  • Crossing Over: Process where two homologous non-sister chromatids pair up and exchange segments of genetic material.

  • Diploid: 2 sets of 23 chromosomes (46 total), noted as 2n.

  • Haploid: 1 set of chromosomes (23 total), noted as n.

  • Meiosis: Cell division for sex cells, producing 4 genetically different cells.

  • Mitosis: Cell division for somatic (body) cells, resulting in 2 genetically identical cells.

Mitosis vs. Meiosis

  • Mitosis:

    • Occurs in somatic (body) cells.

    • Involves one division.

    • Results in 2 genetically identical daughter cells.

    • Used for growth/repair.

  • Meiosis:

    • Occurs in germ cells.

    • Involves two divisions.

    • Results in 4 genetically diverse gametes (sperm or egg).

Meiosis Process

  • Spermatogenesis: Production of sperm from primordial germ cells (1 gamete = 4 sperm).

  • Oogenesis: Production of the egg with 1 gamete = 1 egg cell.

  • Zygote: Fertilized egg ensuring the same number of chromosomes as parents.

Genetics Terms

  • Gamete: A mature haploid used in sexual reproduction.

  • Tetrad: The replicated chromosomes exchange genes during crossover.

  • Heterozygous: Organism with different alleles (e.g., Ff).

  • Homozygous: Organism with identical alleles (e.g., FF).

  • Dominant Allele: Trait expressed even with one copy present.

  • Recessive Allele: Trait expression prevented by a dominant allele.

  • Punnett Square: Tool used for predicting genotype outcomes.

  • Phenotype: Physical appearance based on genetic makeup.

DNA Structure

  • Composed of two strands made up of sugar, phosphate molecules, and nitrogen bases.

  • Chromosome Structure: Consists of chromatids with DNA wrapped around proteins.

  • Chromatin Material: Composed of protein, RNA, and DNA.

Phases of Mitosis

  1. Prophase: Chromosomes condense, nuclear membrane dissolves.

  2. Metaphase: Chromosomes align in the cell's center.

  3. Anaphase: Sister chromatids separate and move to opposite ends.

  4. Telophase: Chromosomes reach opposite ends; nuclear membranes reform.

  5. Cytokinesis: Final stage where the cytoplasm divides, producing two identical cells.

Meiosis Overview

  • Interphase: Precedes meiosis; cell grows and copies chromosomes.

  • Meiosis I: Homologous chromosomes separate into different gametes.

  • Meiosis II: Separates sister chromatids into individual gametes, producing haploid cells.

Genetic Variability in Meiosis

  • Crossing Over: Genetic exchange during Prophase I increases diversity.

  • Random Alignment: Chromosomes align randomly during Metaphase I.

Mistakes in Meiosis

  • Trisomy: 3 copies of one chromosome.

  • Monosomy: Missing one chromosome.

  • Nondisjunction: Failure of chromosomes to separate properly during meiosis II, leading to gametes with abnormal chromosome numbers.

Mendelian Genetics

  • Principles: Dominance, segregation, and independent assortment of alleles.

  • Linkage: Genes on the same chromosome are less likely to be separated during crossover.

Karyotyping

  • Process of arranging chromosomes from largest to smallest for genetic analysis.

  • Involves examining sex chromosomes (XX for female, XY for male).