1.2: Genetics and Heredity

Question 1

What is DNA?

Answer 1

Genetic ‘instruction manual’
Double-helix structure of base pairs (nucleotides)
Contained in chromosomes in the cell nucleus, also in mitochondria

Question 2

How many chromosomes and base pairs do humans have?

Answer 2

46 chromosomes

Approx. 3 billion base pairs

Question 3

Coding DNA

Answer 3

Information on chains of amino acids that dictates protein structure
Coding DNA makes up 1-2% of the genome

Question 4

Non-coding DNA

Answer 4

Has regulatory functions

Question 5

What are proteins for? (5)

Answer 5

Muscle
Amylase (digestive enzyme)
Immunoglobulin (antibodies)
Insulin (hormone)
Red blood cells

Question 6

Gene

Answer 6

DNA that codes for certain traits (e.g. TCHH gene codes for trichohyalin in hair)

Question 7

Allele

Answer 7

Variant of the gene

Question 8

Genotype

Answer 8

Type of relevant genes for a trait (could involve multiple genes and alleles)

Question 9

Phenotype

Answer 9

Trait that is expressed

Question 10

How are chromosomes inherited in sexual reproduction?

Answer 10

23 pairs of chromosomes (46 total)

Inherit one chromosome from each pair from each parent

Question 11

Composition of chromosomes

Answer 11

22 pairs + 1 sexual pair

Sex chromosomes: XX female, XY male

Question 12

Inheritance of sex chromosomes

Answer 12

Y chromosome inheritance is always from father to son

Mitochondria inheritance always from mother to her children

Question 13

Types of traits (5)

Answer 13

Adaptive (increases fitness)
Neutral (no effect)
Maladaptive (decreases fitness)
Discrete (attached/detached earlobes)
Continuous (height)

Question 14

Which process is a problem for maintaining variation with sexual reproduction?

Answer 14

Blended inheritance reduces the variability and competition needed for natural selection

Question 15

Mendelian inheritance

Answer 15

Transmission of hereditary traits in peas (yellow and green, round and wrinkled)
Inheritance works by dominant and recessive traits
This inheritance can be mapped in a punnett square

Question 16

Reason inbreeding is detrimental

Answer 16

Hidden variation (recessive genes) is more likely to be expressed
More likely to have the same recessive genes if related
Many recessive genes are detrimental – harder for it to be ‘selected’ out
Increased risk of expressing detrimental phenotypic traits with inbreeding

Question 17

Two reasons why Darwin dismissed Mendel?

Answer 17

Mendel had no knowledge of genes

Mendel looked at discrete traits, therefore his findings did not explain polygenic continuous traits

Question 18

Who are the three fathers of the modern synthesis/population genetics? What information did they combine?

Answer 18

Fisher
Haldane
Wright

Combined information on evolution and genetics

Question 19

Population genetics

Answer 19

Study of gene frequencies in a population; distribution and change

Question 20

What are the 5 processes that affect gene frequency in a population?

Answer 20

Mutation
Natural selection
Non-random mating
Genetic drift 
Gene flow

Question 21

How does mutation affect gene frequency in a population?

Answer 21

Errors in DNA coding during replication
Introduces new alleles into the population
Starting point for changes in gene frequencies in populations

Question 22

Example of the problem of large effect mutation

Answer 22

Hox genes are conserved genes that determine body plans, a small error in hox genes can cause large errors in body plans
For example, a mutant deficiency in Drosophilla hox genes can cause the small balancing organ to grow into a second wing, which punctuates equilibrium

Question 23

Why are small effect mutations better than large effect mutations?

Answer 23

Series of small mutations are better than large jumps and are commonly selected for because they are more likely to bring positive outcomes

Question 24

How does natural selection affect gene frequency in a population?

Answer 24

Change in frequency of alleles based on selection for adaptive phenotypes and selection against maladaptive phenotypes (relative to the population)

Question 25

Three different types of natural selection

Answer 25

Directional
Stabilising
Disruptive

Question 26

What is directional selection? Provide example.

Answer 26

Changing the average phenotype of a population in one direction
E.g. spread of lactase persistence in Europe; direction selection for lactase production into adulthood

Question 27

What is stabilising selection? Provide example.

Answer 27

Selection against extremes
E.g. human birth weight; higher infant mortality for very low and very high weight babies;
Very low weight babies cannot meet the energetic requirements of the brain
Very high weight babies cannot fit through the vaginal opening in childbirth (obstetric dilemma)

Question 28

What is disruptive selection? Provide example.

Answer 28

Selection against the mean
E.g. If chinook salmon males are medium sized they would be bad at both sneaking and fighting to win females, therefore they are ether small are good at sneaking, or they are large and good at fighting off competitors

Question 29

How does non-random mating/sexual selection affect gene frequency in a population?

Answer 29

More frequent mating with those who display certain phenotypes, then associated genotype will increase

Question 30

How does genetic drift affect gene frequency in a population?

Answer 30

Random changes in population gene frequency

Most likely to happen in small populations and spread by chance

Question 31

What are the two main processes that increase likelihood of genetic drift?

Answer 31

Bottleneck

Founder effect

Question 32

What is the bottleneck effect? Provide example.

Answer 32

Drastic reduction in population, survivors pass on their genes, remaining genotypes are split unevenly

In 1775 a typhoon killed 90% of the population of Pingelap, a Micronesian island. One of the survivors carried a recessive gene for a rare type of colour-blindness. Because of low rates of interbreeding on the island, just under 10% of the population is completely colour-blind.

Question 33

What is the founder effect? Provide example.

Answer 33

Migrating somewhere else and starting a new population

E.g. African diversity and the migration from Africa

Question 34

How does gene flow affect gene frequency in a population? Provide example.

Answer 34

Gene flow between populations can introduce new alleles from one population to the other, which increases variation

E.g. Neanderthals contributed 1-4% of their genes to modern, non-African populations

Question 35

Out of the 5 process that affect gene frequency in a population, which are random and which are non-random?

Answer 35

Random: mutation, genetic drift, gene flow

Non-random: natural selection, non-random mating

Question 36

Epigenetics

Answer 36

The environment and behaviour determines which genes are expressed, which in turn determines behaviour

Question 37

Three types of behaviour that influences gene expression (epigenetics). Give examples.

Answer 37

Stress: poor sleep leads to higher stress levels, leading to higher insulin levels, which increases body weight

Diet: in mammals, disrupted or reduced growth hormone and insulin-like growth factors alters longevity.
Caloric Restrictions also suppresses growth hormone and insulin-like growth factors, which is also associated with extended longevity in animal models.

Love: methylation of genes associated with oxytocin and vasopressin hormones create love and trust that cause voles to mate for life instantly

Question 38

Why would epigenetic mechanisms evolve? Provide example.

Answer 38

Mother prepares the baby using cues of the environment

Maternal gastrointestinal bypass causes 5696 genes to be expressed differently in babies concieved after the bypass (genes associated with heart health and metabolism, insulin levels and weight)

Question 39

Two examples of the paternal-maternal conflict in epigenetics

Answer 39

Genes of paternal origin, expressed in infants, have been selected to favour more intense suckling than genes of maternal origin

Genes of maternal origin may favour slower childhood growth but earlier sexual maturation