- Created by: emily1106
- Created on: 30-11-18 00:06
- Building blocks of life
Amino acids - poly peptides - proteins
- Maintain shape of cells
Gene code for proteins
- Influence the formation of structures in the body and the structure of the nervous system
- Influence events within the nervous system
Father of Genetics
- Gregor Mendel (1822-1884)
- Related organisms
- 8 years he planted 30,000 plants, set out to examine & quanitify the physical traits in pea plants
- Certain particles or "factors" transmitted from parent to offspring
- Mendel suggested that these factors were directly responsible for physical traits
- Each individual had not one but two "factors" for each trait
- Characteristics do not always mix
Crossed plants with one trait with plants with another trait e.g.
- Tall stemmed plants with short stemmed plants
- All of the offspring would be tall stemmed
- If these offspring were then bread with one another their offspring would show a pattern of 1 short stemmed plant to a 3 long stemmed plants.
Certain characteristics are inherited on an "all or nothing basis". No blending.
Inheritence occurs in a predictable way.
- A single pair of genes, one from each parent, determines a particular inherited characteristic.
- Genes control a particular trait can have alternative forms called alleles; e.g. the gene that controls blood type has three alleles A, B, and O.
- When the corresponding genes inherited from the parents are the same, then the individual is homozygous for the trait. They will express that characteristic.
- When the alleles are different, the individual is said to be hetrozygous. For dichotomous traits they will display the charctertistic described by the dominant allele, a charactersitc from a recessive allele will not be expressed.
P1 cross F1 Cross
Phenotypes: tall dwarf Dd x Dd
Genotypes: DD x dd D d D d
Gamete formation F1 gametes
D Gametes d F2 generation
F1 generation F1 gametes D d x D d
D d Random fertilization
Fetilization F2 genotypes DD Dd Dd dd
Dd - all tall F2 phenotypes tall tall tall dwarf
Designation Homozygous - Heterozygous - Heterozygous - Homozygous
Calculating probabilities e.g. red hair
rr rr = rr 100% red hair
rr RR = Rr 100% no red hair
rr Rr = rr Rr 50% chance of red hair
Rr Rr = RR Rr Rr rr 25% chance of red hair
Dominant and recessive traits in humans
- Free ear lobes (dominant) vs. attached ear lobes (recessive)
- Dimples (dominant) vs. no dimples (recessive)
- Straight thumb (dominant) vs. curved thumb (recessive)
- Bent fifth digit (dominant) vs. straight fifth digit (recessive)
- Tongue rolling (dominant) vs. non tongue rolling (recessive)
- Individual can display a characterstic that is intermediate e.g. skin colour
- Expression can depend on the precise compliment of different genes
- Effect of gene may only be seen following some kind of trigger
- Individual can display a characteristic that is contributed to by both alleles, but rather than being intermediate, it is distinctly different from that specified by either allele, this is called co-dominance
E.g. a parent with type A blood and a parent with type B blood will produce an offspring with type AB blood which is different from either A or B types.
- 46 chromosomes (23 pairs)
- Contained in nucleas of every cell except sex cells (gametes) which contain only 23 chromosomes
- 44 autosomal chromosomes, & 2 sex-linked chromosomes: X and Y
- Female 2 X chromosomes, males an X and Y chromosome
- The X chromosome carries many genes, the Y only carries a few genes whcih ensure the developing male foetus becomes 'male'
1. Colour Blindness: Red/green colour blindness is rare in females as they would need both their father and mother to carry the gene. It is fairly common in men as they only need a mother to carry the gene.
2. Haemophilia: Blood clotting disorder, common in the European Royal families. Queen Victoria who carried a recessive gene in one of her X chromosomes. She and all her female family did not show the disease because the defective gene was paired with a dominant non-defective gene. Her male descendants who inherited the defective X chromosome suffered from the disease, and passed it on to their daughters, who in turn passed it down to their sons.
DNA - Deoxyribonucleic Acid
- Superfolded molecule
Sequence of nucleotides:
Bases are linked in a particular fashion (A-T and C-G)
Codon - combination of 3 nucleotides that code for one amino acid.
Human genome project
- Genome = total amount of DNA in one single cell
- Working draft of the Genome was mapped and published in 2001
- 30,000 genes found - these genes provide the recipe for the devlopment of the human body - average gene is compromised of 10,000 nucleotide
- 1000 Genomes Project (2008)
"I do not know of a single psychological trait that does not show genetic influence" Plomin (2018)
- Heritability - the extent to which differences between individuals can be explained by inherited DNA differences.
- Heritability estimates can differ depending on the particular population studies at a particular time.
- Exploring correlations for physcial psychological, & behavioural traits between adoptive parents and children.
- Comparing correlation with those for biological parents & their adopted children.
- Comparing correlations with non-adoptive children & parents.
- Similar process used with adoptive & non-adoptive siblings.
- Example - Colorado Adoption Project
- Monozygotic (MZ) twins - identical twins - share 100% of their genes
- Dizygotic (DZ) twins - Fraternal or Non-identical - twins share 50% of their genes
- Comparing MZ twins reared together & apart e.g. Minnesota Study of Twins Reared Apart
- Comparing MZ and DZ twins e.g. Twins Early Development Study
- Differences in behaviour
- Schizophrenia, mood disorders, anxiety (Plomin et al, 2001)
- Normal variations in personality (Loehlin, 1992) & cognitive abilities (Plomin & DeFries, 1998)
- Television watching (Plomin et al., 1996), lonliness (McGuire & Cliford, 2000), coffee drinking (Cornelis et al., 2011)