Chapter 2 - Mitosis and Meiosis Flashcards
DNA
- Each chromosome consists of one long DNA molecule with hundreds or thousands of genes
- Genes are the units of inheritance
- They encode information for building the molecules synthesized within the cell
- The genetic information encoded by DNA directs the development of an organism
- The molecular structure of DNA accounts for its ability to store information
- Each DNA molecule is made up of two long chains arranged in a double helix
- Each chain is made up of four kinds of chemical building blocks called nucleotides and abbreviated A, G, C, and T
- For many genes, the nucleotide sequence provides the blueprint for making a protein
- Protein-encoding genes control protein production indirectly
- DNA is transcribed into mRNA, which is then translated into a protein
- Gene expression is the process of converting information from a gene to a cellular product
- produce cells for sexual reproduction, unique daughter cells, separation of sister chromatids, separation of homologous chromosomes
Sets of Chromosomes in Cells
- Diploid (2n) cells have two of each type of chromosome
- The two chromosomes in each pair are called homologous chromosomes, or homologs
- Chromosomes in a homologous pair are the same length and carry the same types of genes in the same locations.
Gene
- a particular sequence of nucleotides on a DNA molecule. Carries the code for producing a particular protein
- Sequence of nucleotides determines the sequence of amino acids in a protein
Alleles
- different forms of a gene (different DNA sequence). They may produce a different protein with a different structure and therefore different traits. Ex. A for dominant allele, a for recessive allele
Mutations
- random changes in the sequence of DNA. Likely to occur at S phase. Creates variation.
- What is the effect of a mutation? Mutation can result to evolution. It can also result to genetic disorders
- Nucleotide substitution, Deletion, Insertion
Genotype
- Refers to the two alleles a diploid individual has for a particular gene (HH, Hh, hh)
Phenotype
- refers to the expression of those alleles – physical/physiological/behavioral characteristics (brown fur, large size, yellow seeds, resistant to antibiotics…)
DNA
Deoxyribonucleic acid is an organic chemical that contains genetic information and instructions for protein synthesis
Chromosomes
a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
Homologous chromosomes
The same structural features (e.g., same size, same banding patterns, same centromere positions) The same genes at the same loci positions (while the genes are the same, alleles may be different)
Genes
the basic physical and functional unit of heredity. Genes are passed from parents to offspring and contain the information needed to specify physical and biological traits.
Alleles
one of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location.
Protein
organic compounds made up of amino acids
Enzymes
are proteins that act as biological catalysts by accelerating chemical reactions.
Mutations
random changes in a DNA sequence
Diploid cells
two set of chromosomes
Haploid cells
one set of chromosomes
Homozygous
having two identical alleles of a particular gene or genes.
Heterozygous
having two different alleles of a particular gene or genes.
Mitosis
- produce cells for repair, growth, and replacement. Identical daughter cells, separation of sister chromatids.
Eukaryotic Cell Cycle
- G1 (gap phase 1) - Primary growth phase, the longest phase
- S (synthesis) - Replication of DNA
- G2 (gap phase 2) - Organelles replicate, microtubules organize
- M (mitosis) - Subdivided into 4 phases
- Prophase
- Metaphase
- Anaphase
- Telophase - C (cytokinesis) - Separation of 2 new cells
DNA Replication (S-phase)
- Before replication, each chromosome composed of a single DNA molecule
- After replication, each chromosome composed of 2 identical DNA molecules
Each DNA molecule called a sister chromatid
Held together by proteins
M phase is divided into 4 phases
- Prophase
- Metaphase
- Anaphase
- Telophase
Cytokinesis
- Cleavage of the cell into equal halves
- Animal cells - constriction of actin (protein filaments produce a cleavage furrow)
- Plant cells - cell plate forms between the nuclei
- Fungi and some protists - nuclear membrane does not dissolve; mitosis occurs within the nucleus; division of the nucleus occurs with cytokinesis
Sexual life cycle
- Involves meiosis and fertilization
- Meiosis produces haploid cells
Gametes have only 1 set of chromosomes - Offspring inherit genetic material from 2 parents
Meiosis
- Consists of two cell divisions (meiosis 1 & 2)
- Four haploid daughter cells are produced from a diploid parent cell
- Generates genetic variation among an individual’s gametes via:
- Crossing over and Random Assortment creates different or unique combinations of alleles for the different traits in each gamete.
Crossing over
when chromosomes of the same type are lined up. Parts of the chromosome can be switched. The two chromosomes contain the same genes but may have different forms of the genes.
o Involves homologous chromosomes swapping alleles thereby creating unique combinations of alleles for different traits
o Genetic recombination between non-sister chromatids
o Allows the homologs to exchange chromosomal material
o Creates new combinations of alleles on chromosomes:
And therefore, new combinations of alleles in the gametes produced by an individual
Independent/random assortment
o contributes to the mixing up of genetic material in the gametes, homologous chromosomes are randomly distributed to daughter cells, and different chromosomes segregate independently of each other
o Results in different combinations of maternal and paternal chromosomes (and their different alleles) in the gametes
And therefore, new combinations of alleles in the gametes produced by an individual
