genetics & evolution

• gamete; a mature sexual reproductive cell, such as an egg or sperm cell
• fertilization; the process of fertilizing an egg, involving the fusion of male and female gametes to form a zygote
• • a zygote is a fertilized cell that continues to multiply as it travels the fallopian tube (1-4 weeks gestation)
  • an embryo is attached to the uterus (5-9 weeks gestation)
  • a fetus resembles a baby in the womb (10-42 weeks gestation)
  • a baby is the fetus once it has been born
• haploid cells;

  • one set of chromosomes
  • in humans, number (n) = 23
  • in humans, gametes (sperm & ova) are haploid
• diploid cells;

  • two sets of chromosomes
  • in humans, 2n = 46
  • in humans, all body cells (other than gametes) are diploid
• DNA (Deoxyribonucleic Acid)

  • DNA is found in the shape of a double helix
  • DNA is made up of 4 base pairs;
  • G-C (guanine-cytosine) and T-A (thymine-adenine)
  • DNA is found in the nucleus
  • 20,500-25,000 genes (base sequences at different locations)
  • These genes are spread across 23 chromosomes in humans (each chromosome has 1 very long DNA molecue)
  • When gene codes for a protein, it is said that the gene is expressed
• mutations; an accidental alteration in a genetic message
• chromosomal mutation; an error in the number or structure of chromosomes
• gene mutation; an error in the DNA sequence which affects the expression of a gene
• phenotype; the physical characteristics of a gene (eg. brown hair)
• genotype; the genes responsible for the characteristics of an individual (eg. hair colour)
• alleles

  • in our cells we have 2 sets of chromosomes, one from each parent
  • alleles are different forms of the same gene determining a particular trait feature
• dominant gene; an allele which shows its effect when there is only one allele of that gene
• recessive gene; an allele that is not expressed if the dominant allele is also present
• homozygous; having two identical alleles for a specific characteristic
• heterozygous; having two different alleles for a specific characteristic
• variation; the difference between individuals
• variation is brought about due to an individuals genes that we inherit and the environment we live in
• discrete variation;

  • characteristics where you are either one thing or another
  • inherited and usually controlled by one pair of genes
• continuous variation;

  • there is a full range of in-between stages
  • usually controlled by more than one pair of genes
• mitosis

  • when a cell divides the chromosomes double by replacing themselves and splits once to make 2 new identical cells
  • mitosis produces identical diploid cells so that they can carry out exactly the same functions as the 'parent cell'
  • the function of mitosis is for growth and repair
• meiosis

  • when a cell divides the chromosomes double by replacing themselves, then the cell splits once to make 2 new cells then they split in half again making 4 haploid cells
  • meiosis has many extra stages which creates variation between all the cells produces, ensuring all offsprings are unique
  • the function of meiosis is for reproduction
• artificial selection; the process of breeding animals or plants to produce offspring with desirable characteristics
• evolution; the change in the inherited characteristics of a population over time
• natural selection; the process by which organisms better adapted to their environment tend to survive and reproduce more successfully
• hydrogen bonds; attractive forces that hold the two strands of DNA together
• karyotype; a diagram of the chromosomes of a cell arranged in an orderly fashion
• monohybrid cross; the hybrid of two individuals with homozygous genotypes which result in the opposite phenotype for a certain genetic trait
• nucleotide; a unit built up of a base, a sugar, and a phosphate group
• phosphate; group that alternates with the ribose sugar in the DNA backbone
• triplet code; genetic code made by sequences of three bases in the DNA
• base < gene < chromosome < nucleus < cell
• causes of Mutations

  • radiation
  • accidental DNA damage
  • chemicals found in smoke