Principles of Inheritance

1. Principles of Inheritance

2. Trait: characteristic • Pedigree: a family tree • Progeny: offspring • Cross: mating of two organisms • Gregor Mendel’s (1865) two principles:1. various hereditary characteristics are controlled by factors (genes) in pairs • 2.During formation of gametes, pairs of factors separate. Each gamete receives one set of factors. When two gametes unite, diff traits become evident

3. Mendel’s work in peas (7 pairs of characteristics) included: • Pure breeding: when bred among themselves produce the same traits • Hybrid breeding: genetic info for both traits In addition to defining: • Dominant trait: expressed trait (An allele which will be expressed if present) • Recessive trait: unexpressed trait (An allele which will only be expressed in the absence of a dominant allele)

4. Principle of Segregation: As offspring are formed by the union of male and female gametes, they receive one gene for a trait from each parent.

5. Monohybrid Crosses • only one pair of contrasting characteristics (traits) are being considered • Gene: Segment of DNA which determines a specific trait e.g. eye colour • Allele: Alternate forms (varieties) of the same gene e.g blue or brown • Carrier: An individual who carries the recessive allele but does not express it

6. Genotype: the combination of two or more alleles for a specific trait • Phenotype: The trait which is expresses (physical appearance) • Homozygous: Two of the same allele (AA or aa) • -Heterozygous: Two different alleles (Aa) • 1st filial generation: 1st offspring (F1) • 2nd filial generation: 2nd offspring (F2)

7. Dihybrid Crosses • Two pairs of contrasting characteristics are being considered • One of each trait for each possible section AaBB (female) x AaBb (male) Aa x BB and Aa x Bb

8. Multiple Alleles • Links between gene and chromosome theories: • Both occur in pairs • Both segregate during meiosis and only one member of each pair enters a gamete • Both maintain individuality during segmentation • gene linkage: genes in a particular chromosome forge a set • Homologous chromosomes: pairs of chromosomes with genes for same trait • Locus: point on a chromosome where a gene is located • Multiallelic: more than two possible alleles for a trait, located on a single locus.

9. Polygenic Inheritance: • Monogenic Inheritance: Each person has one pair of alleles for trait • Polygenic Inheritance: Trait shows continuous variation (Dependant on many pairs) • Also affected by environment (diet, exercise, disease etc)

10. Examples of effects of environment on gene expression • e.g. skin colour • melanin: yellow black pigment (made from an amino acid, tyrosine) • Produced in melanocytes (special skin cells) which produce special structures called melanosomes. • Number of melanocytes in all humans is similar but number and size of melanosomes varies between individuals. (larger = darker skin)

11. Examples of effects of environment on gene expression • e.g. skin colour • Variation in amount of an enzyme, tyrosinase, also contributes to varying amounts of melanin production in cells. • Some enzymes produce melanin as a response to UV light but individuals with a lack of these enzymes will generally have fairer skin.

12. Gene Regulation (Regulation of gene expression) • Cells control over the quantity and when a particular protein is made • Structural gene: portion of DNA that contains info for protein synthesis • Promoter: Portion of DNA which indicates the beginning of the structural gene. Enzyme (RNA polymerase) which is transcribing, will only begin after binding with promoter • Specificity Factors: A protein which alters the specificity of RNA polymerase for a given promoter or set of promoters, making it more or less likely to bind to them

13. Gene Regulation (Regulation of gene expression) • Epigenetic factors: factors which make a gene more or less likely to be expressed or inherited.