Genetics

Natural Selection

• Darwin 
• Useful / heritable traits are passed on; traits of less successful individuals are lost
• Those with useful traits produce more offspring
• Therefore there will be more with the useful trait in later generations
• Diversity allows species to adapt to different environments, e.g. the peppered moth
• E.g. owl butterfly - not all adaptations based on camoflage, it can sometimes be useful to stand out
• E.g. changes in domestic animals due to selective brreding

Development of the Human Brain

• Has increased in size during evolution - mainly in cerebrum
• Allows for more complex cognitions but bigger brain doesn't = greater intelligence
• Brain stops growing at around 20 years but always gain new neurons
• Humans have the largest brain size to body weight ratio in mammals (apart from tree shrew)

• Bred sweet pea plants
• Dominant v recessive alleles
• Two dominant or two recessive alleles = homozygous 
• One dominant + one recessive = heterozygous
• One brown plant + one white plant = four brown plants as brwon is dominant
• Two brown plants = three brown plants + one white plant as each parents had one white-seed gene
• Dichotomous traits - two different types of traits

• DNA code / helix identified in 1962
• Genes synthesise proteins
• Banisters = sugars and phosphates
• Rungs = nucleotide bases: adrenine, thymine, guanine and cytosine which are the blueprint for making protein
• A and T pair up; G and C pair up
• Set of genes controlling a trait are found on the same part of the chromosome - called an allele
• DNA pulls apart slightly in the nucleus
• mRNA copies the bases in the nucleus and takes code into cytoplasm - cytoplasm is needed as that's where amino acids are
• Ribosomes read code 3 bases at a time which represents an amino acid
• Amino acids are linked to create a protein

Meiotic

• Sperm and egg cells created in this way - half of each genetic material 
• Sperm - chromosomes duplicate; cell divides to create two cells, each with 23 duplicated chromosomes; each cell divides again to create four sperm cells, each with 23 chromosomes
• Egg - chromosomes duplicate; cell divides to create two cells, one of which dies; egg becomes fertilised then divides to create two cels; the cell without the sperm dies; then the sperm and egg combine to form a zygote with 23 pairs of chromosomes

Mitotic

• Zygote grows in this way
• The 23 pairs of chromosomes duplicate by dividing over and over again

Linkage

• Tendency of traits encoded on the same chromosome to be inherited together
• Use this to find the location of a gene on a chromosome
• If two genes are inherited together more than 50% of the time, this suggests they are linked on the same chromosome
• Disrupted by crossing over 

Human Genome Project

• 1990 - 2003
• Humans have about 20,000 genes
• Led to discovery of 1,800+ disease genes and 2,000 genetic tests so people can learn of their genetic risks for disease

Gender

• Females have 23 matching pairs of chromosomes; men have 22 matching and one pair that is different
• Colour blindness and haemophilia is more common in males than females as they are carried on the X chromosome, not the Y
• Men don't have another X chromosome to counteract the recessive gene so express the trait

Single Genes

• Down syndrome = extra chromosome
• PKU is transmitted by a recessive gene mutation
• Cannot break down phenyalanine (amino acid found in certain foods) so builds up in bloodstream
• Results in brain damage and mental retardation
• Screening injection for babies to test for this
• Women with PKU should go on phenyalanine diet before conceiving

• Maze bright / maze dull experiment to see if intelligence can be influenced by genetics - selectice breeding
• There is some kind of genetic control over intelligence
• Difference between maze bright and maze dull rats was only evident if both were in an impoverished environment
• Much smaller difference for maze dull rats if they were in an enriched environment - suggests environment is a more important factor
• Epigenetics - interaction between genetics and environment

• May be beneficial for older males to be attracted to younger females
• Younger females = healthier = more likely to have healthy offspring / more offspring
• Male mammals are rarely responsible for raising offspring 
• May be due to different energy costs - females put in considerably more than males
• However this isn't always the case, e.g. male seahorses carry their offspring
• Adopting may not appear beneficial
• Ducks and seagulls often adopt - cost of taking on an extra chick is relatively small
• Adoptintg another one outweighs the cost of mistakenly rejecting your own and it's beneficial to have more healthy chicks for the group

Hamilton - R x b - c >0  R = relatedness to recipient  B = benefit to gene pool of act  C = cost of act

• Rule of altruistic behaviour
• Only works if you can recognise your kin
• E.g. bees have a haplodiploid genetic makeup - 75% related to their siblings and 50% related to their offspring, so don't raise their own offspring
• Females pass on more genes by helping to raise sisters rather than their daughters
• Eusocial vertebrates, e.g. naking mole rats are inbred due to the harsh conditions they live in
• Altruism is evident in non-relations, e.g. food sharing in bats
• A set pair share food - beneficial due to harsh environment
• Remebered if a bat didn't share food - cheater

Direct & Indirect Fitness

• Direct - ability to survive and contribute large numbers of fertile offspring to next generation
• Indirect - ability to help kin to survive so they can go on to contribute large numbers of offspring to the next generation