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Question 1

What is phenotype and genotype?

Answer 1

Phenotype: your visible, measurable characteristics
Genotype: your DNA’s genetic composition

Phenotype emerge from the interaction between genotypes and environmental influences, highlighting the dynamic nature of genetic expression.

Question 2

What theory did Darwin accept?

Answer 2

The blending theory which states that mixing red and white produced pink.
That would reduce variation within a population. There must be variation for natural selection to have different traits to select amongst.

Question 3

Mendel solved this problem.

Answer 3

Researched how genetic information is passed from parents to offspring.
He studies pea plants which fertilise themselves, but they can be artificially cross fertilised.

He crossbred the offspring of a line of pea plants that had bred true for yellow peas with the offspring of a line of pea plants that had bred true for green peas.
All cross breeds were yellow peas.

Then Mendel bred these first generation offspring with one another and found that 3/4 of the resulting 2nd generation offspring had yellow peas and 1/4 had green peas.

Question 4

So what did Mendel conclude about blending theory?

Answer 4

Mendel showed that heredity must involve the passing on of specific organic factors, not a simple blending of the parents’ characteristics.

E.g. if he fertilised a plant with purple flowers, with pollen from a white flowered plant, he did not get offspring with light purple flowers, but various % of purple and white flowered plants.

The parents might produce visible characteristics in the offspring, or they might simply be carried for possible transmission to another generation.

Question 5

What did Mendel conclude about the pea plant experiment?

Answer 5

he proposed yellow was a dominant trait and green was recessive. Since yellow hybrids produced both yellow and green offspring, they must have carried the green trait, but unexpressed.

Mendel suggested that each pea plant must carry a double dose of hereditary factors (alleles).

Question 6

What are alleles?

Answer 6

Alleles are different versions of a gene that produce different characteristics.

Organisms that inherit 2 identical genes from each parent for a trait are said to be homozygous for that trait. (AA, aa)

Organisms that inherit two different versions of a gene from each parent for a trait are said to be heterozygous for that trait. (Aa)

Question 7

What is homozygote and heterozygote

Answer 7

Homozygote: organisms that breed true for a particular characteristic - 2 identical alleles

Heterozygotes: organisms that do not always breed true having received different alleles from each parent.

Question 8

What does being heterozygotic mean?

Answer 8

Being heterozygotic doesn’t mean an organism will have phenotype A or B. there are different ways that the genes can express:
- Complete dominance
- Equal blending: it produces half the protein which results in half the pigmentation
- Both phenotypes: heterozygotes express both red and white
- Or a combination of all 3

Question 9

What is a monogenic trait?

Answer 9

Monogenic traits are traits that are determined by a single gene or pair of alleles.

Question 10

What is Phenylketonuria as a monogenic disease?

Answer 10

Associated with mental retardation cause by an excess of essential amino acid (phenylalanine). Affects 1 in 10,000. Parents often do not exhibit the condition.

PKU is based on a recessive allele.
Develops only in homozygous individuals (those who inherit a PKU gene from both mother and father)

Blood of newborn infants is screened for high phenylalanine levels. If the level is high, the infant is placed on a phenylalanine-restricted diet. Diet reduces the amount of phenylalanine in the blood and the development of intellectual disability.

It can be controlled through diet. 100% genetic, but can be controlled through 100% environmental means.
So the genotype is having PKU, but that phenotype through an environmental intervention can mean that they don’t have PKU on a phenotypic level.

The timing of this treatment is extremely important. The diet does not reduce the development of intellectual disability in PKU homozygotes unless it is initiated within the first few weeks of life.

Question 11

What is Huntington’s disease as a monogenic disease?

Answer 11

The inheritance of the condition is based on one dominant allele.
If one parent has Huntingtons, half their offsprings will have Huntington
Symptoms don’t emerge until 40 years

Question 12

What is a polygenic trait?

Answer 12

When multiple genes collectively contribute to specific behaviours.
Schizophrenia is polygenic. Found that 108 separate genes associated with slightly increased risk of Sz.

Question 13

What is DNA?

Answer 13

The storage housing for the information that we get from our parents.
DNA interacts with the environment through epigenetics and it interacts with itself.

Structure discovered by Watson and Crick 1953
Present in every cell of our body

It is made up repeating nucleotides that come in 4 different types. A-T G-C. These are the chemical building blocks of life and they command for every feature and function of our body.

Question 14

What is the genome?

Answer 14

The genome is the entire length of an organism’s DNA.
A gene is a bit of a genome (DNA) that codes for protein

Every cell in your body contains the genetic code for your entire body, as if each house in your community contained a map for every building and road in the entire city.

Question 15

What is behavioural genetics?

Answer 15

How genes and environment interact to form who we are.
Behavioural genetics is a research field that addresses the role of genetic and environmental influences on individual differences in behaviour.

Question 16

Experiments showing that genes affect behaviour

Answer 16

If we can show that behaviour can be influenced by genes does that mean that its all in the genes?

For e.g. MAOA-L is associated with aggression
If a baby is screened at birth and found to have the warrior gene, does this mean they will inevitably grow up to be aggressive?
No

Just because genes affect behaviour, it would be wrong to assume that they determine our behaviour.
All behaviour is based on an interaction of environmental factors and genetic predispositions.

Caspi tested 442 New Zealand males
Those with MAOA-L and who has suffered abuse were 9 times more likely to be antisocial and aggressive.
Interaction of an environmental factor and genes

• small sample
• based on self-report measures which can be subject to recall biases. Participant’s memories of childhood experiences and behaviours may not be reliable

Question 17

Experiment to demonstrate the importance of genes.

Answer 17

Mice were placed in an ‘open field’.
Some mice explore while others are nervous and freeze. DeFries et al 1978 isolated the most confident and the most nervous mice and set up two separate breeding strains to test whether the responses to the open field could be inherited.
The baby mice were cross-fostered.
After a small number of generations, the offspring from nervous parents were statistically more nervous and less explorative than the babies from confident parents.

Question 18

Experiment to demonstrate the importance of environment.

Answer 18

The same effect has been found interbreeding rats that are very quick at finding routes through mazes (‘maze-bright’) versus those that are very slow (‘maze dull). However, the effect can be eradicated by raising the rats in different environments. Usually they are raised in rather empty uninteresting cages.
Cooper and Zubek (1958) - if they are raised in enriched cages with lots of other rats, then the rats from the ‘maze dull’ family lines will perform just as well ‘maze bright’ rats. Emphasises the importance of the interaction between genes and environment.

• like any studies with animals, it is hard to generalise to humans

Answer 19

It is easier to understand the genetics of a behavioural disorder than it is to understand the genetics of normal behaviour.

Mnay genes influence the development of a normal behavioural trait, but it sometimes takes only one abnormal gene to screw it up. - PKU

Question 20

Why do we use twin studies?

Answer 20

Using twin studies, researchers can apply a number of statistical techniques to estimate the extent to which differences among people are due to genetic differences.

2 types: MZ and DZ

When MZ twins are more similar on a trait it is a clue that genetics are important

Identical twins reared together, tend to be more similar for some characteristics than those reared apart, indicating the environment also makes a difference

Question 21

Why do we use adoption studies?

Answer 21

If adopted children are more similar to their adoptive parents, suggests environmental influence, if more similar to biological parents, suggests genetic influence.

In one study, Kety (1978) identified adoptees who were diagnosed with schizophrenia in adulthood. They examine the backgrounds of the biological and adoptive parents and relatives to determine the rate of Sz.
It was found that 12% of biological family members had also been diagnosed with Sz, compared with a concordance rate of only 3% of adoptive family members.

Question 22

The Minnesota

Answer 22

The Minnesota Study of Twins Reared apart involved 59 pairs of MZ and 47 pairs of DZ

Adult MZ twins were more similar to one another on all psychological dimensions than were adult DZ twins, whether or not both twins of a pair were raised in the same family environment.

• relatively small sample size
• it is unethical to separate twins so that can’t be practiced anymore so we can no loner research MZ twins reared apart

Question 23

Heritability

Answer 23

In order to quantify the contributions of genetic variations in a particular study, researchers calculate heritability estimates.

Heritability are estimates of differences between individuals in a population, with regards to a particular trait, due to genes.

Bouchard (1998) estimated the heritability of IQ to be 0.7

However, you have to interpret heritability estimates carefully because genetic and environmental factors interact.
This does not mean that IQ for all humans on the planet is 70% genetic and 30% environmental.

Genetic similarity in Bouchard’s IQ data accounted for 0.7 variation only relative to that particular study and sample

Heritability estimates apply to specific populations at specific times - 300 years ago there wasn’t equal access to education so the variation in education levels would be much bigger and much more of the variance would be accounted for by the environment

Question 24

What is a candidate gene?

Answer 24

A candidate gene refers to a gene that is believed to be related to a particular trait.

Question 25

What are epigenetics?

Answer 25

Epigenetics is a change in genetic activity without changing the genetic code.

Lifestyle and events we encounter leave chemical marks on our DNA that determine how much or little of the genes is expressed. The collection of chemical marks is known as the epigenome.

Today technology advances have enabled scientists not only to map the human genome but also to duplicate and modify the structures of genes themselves

Question 26

What are transgenerational epigenetics?

Answer 26

Stressor and memories can be passed to multiple generations of offspring in ways that meaningfully affect their behaviour.
For example:
it has been shown that when mice experience an odour associated with a painful shock, the memory of that experience is passed on to generations through epigenetic mechanisms

Question 27

Strength of epigenetics

Answer 27

In 1944, the Nazis blocked the distribution of food to the Dutch people and 22,000 died of starvation.
Susser and Lin found that women who became pregnant during the famine had low birth weight babies who were twice as likely to develop Sz.
This suggests that the life experiences of previous generations can leave epigenetic markers that influence the health of their offspring.