genetics

• What are chromosomes?


  Thin strands/ thread-like structures of DNA
• Where are chromosomes found?


  In the nucleus of cells.

  
• What are chromosomes subdivided into?


  Genes.
• how many chromosomes are found in human cells


  46 chromosomes in body cells, arranged in 23 pairs
• genes


  sections of chromosomes that code for characteristics and that are short lengths of DNA
• why are gametes different than body cells?


  have 23 chromosomes (haploid)
• genome


  The entire genetic material of an organism
• allele


  different forms of the same gene
• what is the backbone of DNA made of?

  alternating phosphate and deoxyribose sugar

  
• base pairing in DNA

  A-T (adenine-thymine); G-C (guanine-cytosine)
• what does a nucleotide consist of


  1 phosphate, 1 sugar and 1 base
• structure of DNA


  A phosphate and sugar backbone with interlinking bases to form a double helix

  
• how many bases code for one amino acids


  3 bases (a base triplet)
• Where is the DNA code (sequence of bases) found?


  The DNA code is found on the coding strand.
• What is the importance of arranging base triplets in the correct order on the coding strand?


  to ensure the correct protein is made, which is known as the base triplet hypothesis.
• what happens in a mutation


  there is a change in the order of bases which changes the final protein which the cell produces

  
• what is mitosis used for

  grow or to replace worn out cells and to repair damaged tissue an asexual reproduction
• what does mitosis produce?


  two new cells (daughter cells) in one division
• describe the daughter cells produced in mitosis

  genetically identical (clones) to the parent cell and each other
• what does mitosis ensure


  that every cell in the growing organism contains the same genes and chromosomes
• describe the process of mitosis

  1. Chromosomes become visible in the nucleus

  2. Chromosomes duplicate, splitting lengthwise into two identical chromosomes joined by a centromere.

  3. The nuclear membrane disappears and spindle fibers form one end of the cell to the other. Chromosomes line up along cell's equator. Each duplicated chromosome attaches to an individual spindle fiber

  4. The spindle fibers pull towards the end of the cell, so the replicated chromosome splits completely.

  5. A new nuclear membrane forms round each new set of chromosomes and 2 identical daughter cells are formed

  
• where does meiosis occur


  testes and ovaries, producing gametes (sperm and egg cells)
• what is meiosis used for


  sexual reproduction

  
• stages of meiosis


  MEIOSIS |

  1. Each chromosome duplicates, forming two identical chromatids (sister chromatids) which become visible

  2. Homologous chromosomes pair up (maternal and paternal chromosomes) and attach to spindle fibers formed from the breakdown of the nuclear membrane

  3. The fibers separate, pulling the chromosome pairs away from each other

  Results in 2 haploid cells

  
• what is meosis


  reduction division - one cell producing four genetically different haploid daughter cells and through independent assortment reassorts the chromosomes to provide variation
• Does mitosis produce haploid or diploid cells?


  diploid (46 chromosomes)

  
• Does meiosis produce haploid or diploid cells?


  haploid (23 chromosomes)

  
• how many daughter cells produced in mitosis


  2 identical daughter cells
• how many daughter cells produced in meiosis


  4 daughter cells
• dominant allele


  the allele which is always expressed even if only one copy of that allele is present
• recessive allele


  An allele that is masked when a dominant allele is present - only expressed if two copies are present
• genotype


  genetic makeup of an organism / the specific genes an individual has for a particular characteristic
• phenotype


  the observable trait displayed by an organism as a consequence of its genotype
• homozygous


  refers to a pair of alleles at the same locus which are the same
• heterozygous


  refers to a pair of alleles at the same locus which are different
• test cross


  an experiment used to determine an organism's genotype by crossing with a homozygous recessive individual

  
• homologous chromosomes


  Chromosomes that have the same sequence of genes and the same structure
• What does a monohybrid cross involve


  the inheritance of a single characteristic.
• How many recessive alleles must be present to express the recessive trait in a monohybrid cross


  Two recessive alleles
• what observation did gregor mendel make


  pea plants had characteristics that varied from plant to plant.