Genetic variation and inheritance~

• A gene is a section of DNA on a chromosome, codes for a particular sequence or amino acid.
• Most of our characteristics are controlled by multiple genes.
• An allele is a different form of the same gene.
• Chromosomes occur in pairs.
• Most genes come in pairs.
• Each allele comes from the parents in sexual reproduction.
• If a person has two alleles that are the same they are called homozygous. (You can either be Dominant or Recessive)
• If a person has two alleles that are different they are heterozygous.(have both a dominant and recessive allele)
• The stronger allele is referred to as dominant.
• The weaker allele is referred to as recessive.
• A genotype is a set of alleles that an organism has, expressed as the phenotype.
• 3 possible genotypes:

  -BB

  -Bb

  -bb
• A phenotype is the visible characteristic of an organism.
• 2 possible phenotypes:

  -Black

  -Yellow
• To determine the characteristic that an offspring may have we use a punnet square.
• The famous scientist that is known for his work on inheritance is Mendel.
• The dominant allele is written first.
• The first generation of a cross is referred to as the F1.
• The definition of self-pollinating / selfing is when the f1 genotype is crossed with itself.
• The second generation is referred to as the F2.
• Chromosome pair number 23 determines the sex of an offspring.
• If the sex chromosomes are the same the gender of a human would be a female.
• If the chromosomes are different the gender of a human would be a male.
• The female sex chromosomes are XX.
• The male sex chromosomes are XY.
• The possible number of sex chromosomes that a female can put into her egg is 1.
• The possible number of sex chromosomes that a male can put into his sperm is 2.
• The females is X.
• The males is X and Y.
• The father's sperm determines the sex of the offspring.
• Every time fertilisation happens, the probability of having a girl is 50%.
• Every time fertilisation happens, the probability of having a boy is 50%.