Genetics and Behaviour Flashcards
what did Darwin say about natural selection?
“Evolutionary change occurs as the heritable traits of successful individuals are spread throughout the population, whereas those traits of less successful individuals are lost.”
Darwin 1859
example of natural selection
peppered moth variation depends on environment
what happened to the human brain during evolution?
the human brain has increased in size during evolution
most of the increase in size occurred in the cerebrum
increased convolutions in the cerebrum have served to increase the volume of the cerebral cortex
what mammals have the highest brain size to body weight ratio?
humans and tree shrew
how much of the total body weight of humans and elephant makes up the brain?
the human brain makes up 2.3% of the total body weight
the elephant brain makes up 0.2% of it’s total body weight
how much does the brain weigh at birth and how many neurones does it contain?
it weights an average of 350g containing about 100 billion neurons
production of new neurons almost ceases, except in the hippocampus and olfactory bulb but those that are already present grow and establish connections with each other
how much does the adult brain weigh and when does it fully develop?
the human brain reaches its adult size of around 1400g and doesn’t develop until late adolescence
how much DNA do humans share with chimpanzees, orangutans and gorillas?
chimpanzees and humans - 1.2%
orangutans and humans - 2.4%
gorillas and humans - 1.4%
how did humans and chimpanzees lineages diverged?
humans and chimpanzee lineages diverged from a common ancestor about five to six million years ago
which species played a significant part in human evolution and how?
the genus Homo was derived from Australopithecus (Southern Ape) at some time after three million years ago
the first hominid to leave Africa did so around 1.7 million years ago (Homo erectus)
Our own species, Homo sapiens, evolved in East Africa around 100,000 years ago
explain Mendel’s theory
Austrian Monk bred true pea plants together
first generation: he crossed brown seeds and white seeds to produce all brown seeded peas because they all have one dominant brown seed allele and one recessive white seed allele
second generation: he crossed brown seeds with brown seeds to produce 75% brown seeds and 25% white seeds because 1 in 4 had 2 recessive alleles which became dominant
define allele
two versions of the same gene
set of genes controlling a trait that sit at the same site of the chromosome
define chromosome
strands of DNA
define gene
a piece of DNA that directs protein synthesis
define dominant allele
only one copy is required to express the trait
define recessive allele
two copies are required to express the trait
define genotype
genetic makeup of alleles
define phenotype
observable trait from the combination of alleles
define homozygous
when both alleles are the same e.g. BB or bb
define heterozygous
when the alleles are different e.g. Bb
what is DNA?
deoxyribonucleic acid, in the nucleus of each cell, contains the alleles
double helix structure
made of sugar phosphate backbone with nucleotide bases
what are the nucleotides and which ones attach to each other?
adenine
thymine
guanine
cytosine
A <–> T
C <–> G
what did Watson and Crick (1962) find?
they deciphered the DNA code
found that humans have 23 pairs of chromosomes
explain the process of protein synthesis
- the DNA molecule partially unravels exposing the structural gene that is to be expressed
- transcription occurs: a strand of messenger RNA is transcribed from one of the exposed DNA strands and carries the genetic code from the nucleus into the cytoplasm of the cell
- translation occurs: in the cytoplasm, the strand of messenger RNA attaches itself to a ribosome. the ribosome moves along the strand translating each successive codon into the appropriate amino acid, which is added to the lengthening protein by a molecule of transfer RNA
- when the ribosome reaches the end of the messenger RNA strand, a codon instructs it to release the completed protein
how do mutations occur?
transcription or translation errors
define gametes
sex cells e.g. sperm cells, egg cells
how are sperm cells created and the process
sperm cells are created by meiotic division
1. the fathers body cells have 23 pairs of chromosomes
2. the chromosomes duplicate themselves
3. the cell divides to create two cells each with 23 duplicated chromosomes
4. each cell divides again to create 4 sperm cells, each with 23 chromosomes, which is half the normal number
how are egg cells created and the process
egg cells are created by meiotic division
1. the mother’s body cells have 23 pairs of chromosomes
2. the chromosomes duplicate themselves
3. the cell divides to create 2 cells, each with 23 duplicated chromosomes, one of these cells dies
4. fertilisation occurs
5. the fertilised cell divides to create two cells, the cell without the sperm dies
6. the sperm and the egg combine to form a zygote with 23 pairs of chromosomes
how does the zygote grow and the process
the zygote grows by mitotic division
1. the zygote has 23 pairs of chromosomes: half from the mother, half from the father
2. the chromosomes duplicate
3. the cell divides to create 2 cells each with 23 pairs of chromosomes
4. mitotic division occurs over and over until an adult organism is created
explain the process of DNA replication
- the two strands of the original DNA molecule unwind
- the nucleotide bases on each strand attract free-floating complementary bases
- two identical DNA molecules are created, each with one strand from the original DNA molecule and one new strand
how many chromosomes do humans have?
humans have 23 pairs of chromosomes
how many pairs of chromosomes determines gender?
what are the chromosomes that females and males have?
gender is determined by 1 pair of chromosomes
all females have XX chromosomes
all males have XY chromosomes
Y chromosome is smaller
examples of sex-linked traits
colour blindness and haemophilia
explain haemophilia
haemophilia is more prevalent in males than females
dominant H = do not have haemophilia
the gene for haemophilia is carried on the X but not Y chromosome
females can be heterozygous or homozygous: HH, Hh, hh
males can only have one gene: H, h
disorders associated with single genes
down syndrome is caused by a chromosomal aberration resulting in an extra 21st chromosome
single gene metabolic disorder Phenylketonuria (PKU)
explain PKU disorder
discovered by a Norwegian Dentist called Asbjorn Folling
PKU is transmitted by a recessive gene mutation on chromosome 12
cannot break down phenyalanine, amino acid common in food
as a result build up in blood resulting in brain damage
hospitals screen babies for high levels of this amino acid
reduction of phenyalanine in diet relieves symptoms
explain the Maze Bright Maze Dull study
Tryon (1934) Genetic control of cognitive ability
Tryon ran a normal population of rats in a maze and separated out the ones that were really fast at learning the maze and ones that were really slow and allowed these two groups to breed separately.
he then did the same with the two groups offspring.
separating out the smart ones and breeding them and the dull ones and breeding them
by the 8th generation the two groups behaviour in the maze was completely different.
all of the animals in the bright group learnt the maze quickly and all of the animals in the dull group learnt it slowly
explain the variation of the Maze Bright Maze Dull study
Cooper and Zubek found that the difference between the maze bright and maze dull rats was only seen if both groups were in impoverished environments.
if the environment was enriched the impairment in the maze dull was removed demonstrating the importance of environment
define dizygotic
from two eggs individually fertilised
fraternal twins
define monozygotic
from one egg split after fertilisation
identical twins
explain the Minnesota study of twins
Bouchard (1998) Twin studies
twins reared apart showed that identical twins were more similar than fraternal twins on all psychological dimensions
Turkheimer et al (2003)
found heritability of IQ was near 0 in impoverished twins and near 1 (maximum) in affluent twins
summary points
Mendel showed traits could have two variations, one dominant, one recessive.
These codes for these traits are held in our DNA in groupings of nucleotide bases (genes)
Half of our DNA is passed to our children
Some disorders can be caused by the presence of a single recessive gene on a male X chromosome (Haemophilia)
Some can be caused by mutations of single genes (PKU)
Cognitive ability can not only be influenced by genes but also by the environment
example of advantageous behavioural traits
older males attracted to younger females –> produce healthier offspring
examples of advantageous behavioural traits in humans that might not appear advantageous
young females attracted to older males –> social dominance is adaptive –> dominant males produce more offspring than non-dominant males
examples of advantageous behavioural traits in animals
some animals adopt other animals offspring –> doesn’t change the survival chances of their own offspring much –> cost-benefit
evolutionary pressure to take on imposter offspring –> overrides costs of mistakenly rejecting your own (Fisher, 2003)
some animals cannot identify their own chick and adopt other ones –> better to have a healthy chick to give food to (Saino et al., 2000)
define sentinel behaviour
looking out for predators and giving an alarm call is advantageous to the individual
meaning that the animal will survive longer and have more offspring
what do you get from risking your own life to protect others?
most behavioural biologists are skeptical about group-benefit group selection because if hereditary characteristics benefit a group but harm an individual’s chances of reproducing, they will be eliminated over time no matter how good they are for the group
all the altruistic ones that survived, it will be their genes that are passed onto the next generation
sentinel behaviour - Clutton-Brock (1999)
define altruistic behaviour
when animals behaviour benefits other individuals, even to the potential detriment of themselves
what is direct fitness?
- sentinel behaviour in meerkats is adaptive as it leads to direct fitness which helps the individual
- trait that will increase ability to survive and contribute large numbers of fertile offspring to the next generation
- sentinel behaviour provides an advantage to the individual as it is the first to see the predator and so it is the first escape
- it does not have a disadvantage in terms of stopping it feeding as the individual will only engage in the behaviour after it has finished feeding
what is indirect fitness?
- alarm calling in Belding’s ground squirrel - Sherman (1977)
- making shrieking noises makes them more vulnerable to getting eaten
- this is a big disadvantage however as they are surrounded by family they are more likely to be saved by those with similarities to them
- by saving their family, more of their genetic material is passed on
- trait increases ability to help kin survive and contribute large numbers of fertile offspring to the next generation
- the animal making the alarm is most likely to get eaten so it does not benefit the individual but it does benefit others in the colony
what evidence that this behaviour provides indirect fitness by saving kin?
only females make alarm calls
other than direct offspring, males are not related to rest of colony so do not gain enough indirect fitness by saving others
females are more likely to stay in the home area
males more likely to spread to different colonies to increase genetic diversity
only works if you recognise the kin
how do you work out when there is enough benefit from indirect fitness from altruistic behaviour to evolve?
Hamilton (1964) the general evolution of social behaviour
Hamilton’s rule of altruistic behaviour would evolve if relatedness to recipient and benefit to the gene pool outweighs the cost
R x b - c > 0
R = relatedness to recipient
b = benefit to the gene pool of act
c = cost of act
how does kin selection work?
only works if you can recognise your kin
Belding’s ground squirrels are less aggressive and more altruistic to half siblings reared apart than to unrelated individuals reared apart
Holmes (1986) animal behaviour
kin selection in humans
Mothers can recognise photographs of their infants within 33hrs of birth and strangers can match photographs of mothers and infants, suggesting a physical resemblance among kin (Porter et al. 1984)
Mothers can pick out their children’s smelly t-shirts (Porter and Moore, 1981)
Both mothers and fathers reliably recognise their infant’s cries (Gustafsson et al, 2013)
kin selection in swallows
Communal Bank swallows are able to identify their on kin which gives them an advantage on their genes are more likely to be passed on (Beecher, Beecher and Hahn, 1981)
Solitary Tree swallows couldn’t identify kin from calls but this skill is not needed as they don’t come across other offspring as much (Leonard et al, 1997)
extreme altruism
bringing up sisters instead of daughters
Eusocial societies in Hymenoptra species e.g. bees, termites, wasps
Bourke (1997) Kin selection in insects
societies which exhibit extreme altruism:
- cooperative care of brood
- reproductive division of labour
- overlapping adult generations
explain extreme altruism in Hymenoptra species
Worker bees bringing up more and more generations that are not their own offspring. This occurs due to their genetic makeup:
Females have 2 pairs of chromosomes - one from male and one from female - diploid - and are created from a fertilised egg
Males have 1 pair of chromosomes - one from female - haploid - and are created from an unfertilised egg
This means that sisters are share 75% of genes rather than 50% making them more related
As a result, a female passes on more of their genes by helping to raise sisters than flying off and raising daughters
extreme altruism in eusocial vertebrates
Naked mole-rats (Honeycutt, 1992)
like bees they have a division of labour, queen largest and long-lived, other females do not breed
unlike bees they are diploid and have no difference in physiology
factors leading to eusocial society
inbreeding
living in a contained nest
harsh conditions outside of next
benefits of extreme altruism
small genetic diversity leads to being more related to your sisters than offspring
so acting to protect your brothers and sisters is more beneficial to your gene pool
altruistic behaviour in non-eusocial vertebrates
- Emlen (1997)
- Florida Scrub Jays help siblings as it will increase indirect fitness
- 3/4 adult birds e.g. mother, father, brothers, sisters feeding 1 fledgling
- Having helped out at the nest, they learn how to bring up the next generation which increases the likelihood that they can bring up their own fledglings
- indirect and direct fitness
