Chapter 4- Molecular genetics and development

Question 1

Why are studies on molecular genetics considered proximate analyses?

Answer 1

Genes can be used in proximate rather than just ultimate explanation of a trait. Studying which specific allele or set of alleles in responsible for trait means that we are viewing genes as a proximate factor. For example, if allele 1 is associated with behavior X, then we’re looking at the trait through a proximate perspective

Question 2

How does termite sociality demonstrate the link between developmental and molecular genetic proximate approaches?

Answer 2

In termite colonies, the queen of the colony produces nearly all of the offspring. We can examine what the molecular genetic proximate basis is for workers during development that causes them not to reproduce even though they are capable of doing so. When the queen of the colony dies, the workers because aggressive, and a queen is determined as a result of these interactions. It was hypothesized that not reproducing was due to the queen chemical signaling the workers. When researchers used RNAi techniques to silence the expression of a queen’s Neofem2 gene, the behavior of the workers became more aggressive, as if they were appointing a new queen. This suggests that pheromones from the Neofem2 gene are responsible for suppressing worker reproduction

Question 3

Mendel’s laws

Answer 3

Includes the principle of segregation and the law of independent assortment

Question 4

Principle of segregation

Answer 4

Each gene is a separate unit, with one of each being inherited from each parent. Only one of the two gene copies present in an organism is distributed to each gamete (egg or sperm cell) that it makes, and the allocation of the gene copies is random. When an egg and a sperm join in fertilization, they form a new organism, whose genotype consists of the alleles contained in the gametes.

Question 5

Law of independent assortment

Answer 5

The alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene. This is only true for unlinked loci, however.

Question 6

Recessive alleles

Answer 6

Two copies of an allele are necessary for expression of the trait

Question 7

Dominant alleles

Answer 7

A single copy of an allele is necessary for expression of the trait

Question 8

Satellite and independent male ruff birds

Answer 8

Males display one of two behavioral strategies during mating season. Independent males make up of the majority of individuals and guard small mating territories. Satellite males don’t defend their own territories, but temporarily share the independent male’s mating area. They basically form an alliance with the independent male to attract females. Independent and satellite males also differ in coloration and body mass. Satellite males are smaller and have lighter plumage than independents.

Question 9

How are the differences in mating types in male ruff birds controlled?

Answer 9

They are mostly controlled by a single gene containing S and s alleles. The S allele is dominant and codes for satellite behavior, while the s allele is recessive and codes for independent behavior if two alleles are inherited.

Question 10

Polygenic behavioral traits

Answer 10

Traits associated with variation at more than one locus- when a trait is controlled by more than one gene. There are often sets of genes that each contribute a small amount to the trait. These traits do not follow Mendelian rules of inheritance

Question 11

Quantitative trait loci

Answer 11

Behavioral geneticists can conduct searches for a set of genes that contribute to a trait.

Question 12

QTL mapping

Answer 12

A way of finding the general region of the genome in which quantitative trait loci reside. Marker loci are used, which are easily evaluated by not related to the trait of question. They can be used to help identify the approximate locations of the unknown alleles that are related to the behavior of interest

Question 13

How does QTL mapping work?

Answer 13

1. Select two parental strains that differ in their values of the quantitative trait and differ at a set of marker alleles
2. Cross these 2 strains to produce offspring (the F1 generation). Typically they will manifest intermediate values of the quantitative trait
3. Cross F1 individuals to produce an F2 generation. Their genotypes are measured at the marker loci, and the value of the quantitative trait is measured. This information is used to determine which marker loci are most closely associated with QTLs for the trait

Question 14

QTLs and fear/fearlessness in mice (Flint)

Answer 14

*Goal- to study fear and anxiety by recording open field behavior in mice
*Background- open field behavior measures fear when animals are placed in large and open environments that are well lit.
*Method- used 2 genetic lines of mice, one that had been bred for high open field activity and one that was bred for low open field activity. Their behavior was measured in open field tests and their fear/anxiety response was measured when placed in mazes. They collected DNA from the fearful mice.
*Results- able to identify QTLs for fear on 6 mouse chromosomes from the open field tests, but only on a subset of the chromosomes for the maze tests

Question 15

mRNA and honeybee foraging (Toma)

Answer 15

Built on earlier studies indicating that the period (per) gene influences circadian rhythms in fruit flies. Measured mRNA levels in the brains of 3 groups of honeybees of different ages. The bees were recaptured at specific time intervals so their per mRNA levels could be measured. Per mRNA was significantly greater in older individuals that foraged for food and brought food to their colony compared to younger bees that stayed at the hive. When age effects were eliminated as a confound, early foragers had per levels that did not differ from older foragers. This suggests that per mRNA is linked to foraging rather than to development.

Question 16

Manganese transport to the honeybee brain (Shahar)

Answer 16

*Goal- to examine the effect of the gene malvolio (mvl) on manganese transport to the brain, and its implications for foraging
*Background- foragers that specialize in collecting pollen have a higher responsiveness to sucrose than those that specialize in nectar foraging, and both types of foragers have a stronger response to sucrose than younger nurse bees in the hive. The mvl gene affects the way fruit flies respond to sucrose.
*Results- found that the amount of manganese in the head of a honeybee and the amount of mvl mRNA in the honeybee brain were high in the bees that foraged pollen and nectar, and low in nurse bees that stayed in the hive

Question 17

Which genes are associated with bird songs?

Answer 17

The expression of the FOXP2 gene in certain brain regions is associated with both song perception in birds and language acquisition in humans. When the FOXP2 gene is knocked out, the ability of birds to copy the songs of adult birds is severely impaired

Question 18

What does it mean for a gene to be knocked out?

Answer 18

It means the gene was deactivated

Question 19

Zebra finch song perception

Answer 19

Levels of mRNA in the forebrain were measured as the birds were exposed to songs. This area is associated with song pattern recognition, song discrimination, and the processing of auditory cues in birds. mRNA levels associated with the zenk gene. In addition, zebra finches exposed to the song of another species showed reduced zenk mRNA responses, and the birds did not experience an increase in mRNA activity in the “no song” condition.

Question 20

Habituation

Answer 20

When an animal’s responses begin to decrease and return to baseline after it is exposed to the same stimulus over and over. In zebra finches, they no longer experienced an increase in mRNA responses after they had been exposed to the same song multiple times.

Question 21

Vasopressin receptors are coded for by which gene in prairie voles?

Answer 21

Vasopressin receptors are controlled by the avpr1a gene. This gene contains a long version allele and a short version allele. The long version of the avpr1a allele is more strongly associated with prosocial behaviors like parental care and interactions with mates

Question 22

Within species variation of vasopressin receptors in prairie voles study (Hammock and Young)

Answer 22

Researchers bred two lines of prairie voles- one line was homozygous for the long version of the avpr1a allele, and one was homozygous for the short version. If the avpr1a allele was responsible for male behaviors toward mates and offspring, then males from the two lines should display different social behaviors, and the results were consistent with this hypothesis. Males homozygous for the long version of the allele displayed more caretaking behaviors for pups and responded more positively toward familiar females

Question 23

Synonymous vs nonsynonymous mutations

Answer 23

Synonymous mutations do not change amino acid sequence and therefore have no effect on fitness. Nonsynonymous mutations change the amino acid sequence and have fitness consequences. Differences between synonymous and nonsynonymous mutations allow researchers to measure the strength of natural selection at a locus.

Question 24

Genomics of cognition in great tits (Laine)

Answer 24

From an ultimate perspective, researchers found that many genes linked to cognition were overrepresented in areas of the genome that showed evidence for positive natural selection. There was positive selection on the EGR1 gene, which is linked to memory, learning abilities, and song learning in birds. There was also strong selection on the FOXP2 gene

Question 25

Why do different species display similar suites of behaviors even if they aren’t phylogenetically related? (Rittschoff)

Answer 25

Researchers examined 3 species- the house mouse, three-spined sticklebacks, and the honeybee. Individuals from each species were exposed to either a territorial intruder or a neutral object, and then their mRNA was sequenced. Responses to territorial intrusion in all species involved a toolkit of GPCRs, which are involved in hormonal and neurobiological processes associated with behavior. There were also similarities in the expression patterns of many genes linked to territoriality.

Question 26

Gene expression patterns

Answer 26

All multicellular animals develop from a single cell, but every cell (except gametes) contain the same set of genes. Early in development, an embryo’s cells are totipotent and can develop into any cell type. The cell type they eventually become depends on the manner in which genes are regulated and expressed in a cell’s environment.

Question 27

What controls the cellular differentiation process?

Answer 27

Transcription factor proteins- they guide development by binding to regulatory enhancers

Question 28

Regulatory enhancers

Answer 28

A section of DNA that lies outside of that gene but is involved in regulating the timing and level of that gene’s expression. The level of a gene’s expression is determined by the amount of product (proteins) a gene produces. Regulatory enhancers are noncoding, but they act as “switches” to turn a gene on or off. This explains why every cell has the same set of genes but does different things

Question 29

How is a gene turned on?

Answer 29

Transcription factor proteins bind to the regulatory enhancer, and they trigger RNA polymerase to start transcribing an RNA copy of the gene.

Question 30

Development

Answer 30

A broad term that describes many things from in utero effects to effects the environment might have on an individual throughout their life. This includes abiotic and biotic factors.

Question 31

How does temperature cause developmental differences in some species?

Answer 31

Temperature has strong effects on olfactory senses in insects. This has fitness effects because olfaction is the main way that insects interact with their environment. In the parasitoid wasp, researchers examined how temperature that embryos were exposed to during development affected their ability to find suitable hosts for their eggs later in life. There were two experimental treatments at 4 degrees Celsius, each lasting a different amount of time. The results indicated that exposure to cold temperature during development significantly impacted the number of eggs a female laid inside a host and the female’s ability to identify a good host. Exposure to cold temperature also negatively impacted the ability of females to learn to avoid an already parasitized host.

Question 32

How does variation in parental care affect behavioral development of prairie voles?

Answer 32

Some pups are raised by just their mother, both parents, or in communal nests. Pups in the biparental groups received significantly more grooming and licking behavior than single mother pus. Later on in life, there were differences in social behavior. SM females licked and groomed their pups less than BP individuals. Also, both males and females from the SM group took longer to find a mate and bond with them than individuals from the BP group

Question 33

Effect of the nest environment in cichlids

Answer 33

In this species, the young are raised by parents and by older siblings that act as helpers. Researchers hypothesized that the presence of parents and siblings provide younger individuals with skills that are beneficial for species that live in complex social groups. It frees up time for the offspring to interact with others instead of being vigilant for predators, and also serves as role models for the offspring. Fish raised with either adults or adults and helpers displayed behaviors that were less costly in terms of energy but were still effective in defending their territories compared with other fish that were raised without parents or helpers. The reason for this is unclear.

Question 34

Parenting experience in oldfield mice

Answer 34

In oldfield mice, so females remain at the nest and help their mothers raise the next litter of young. Researchers tested whether females that helped take care of siblings were better mothers to their own offspring. They were able to experimentally create experienced and inexperienced females. The litters of experienced females had a higher probability of survival than those of inexperienced females, due to experienced females building better nests

Question 35

Supergenes

Answer 35

Two or more genes that are linked together and inherited together. They consist of multiple tightly linked loci that regulate a system of discrete phenotypes. Occurs in ruff male birds.

Question 36

Linked traits

Answer 36

Linked traits, like hair and eye color, are inherited together, probably because they are located on the same chromosome. Not the same thing as supergenes. They go against Mendel’s law of independent assortment.

Question 37

Heat maps

Answer 37

Used to indicate the level of gene expression in an animal, going from no-high expression

Question 38

Epigenetics

Answer 38

Methylation and acetylation pattern on a histone can be
inherited. Methyl groups inhibit transcription, while acetyl groups favor transcription

Question 39

How will identical twins begin to differ genetically over time?

Answer 39

Even when reared in the same environment,
strong phenotypic differences exist later in life for monozygotic twins. As identical twins age, epigenetic
modification patterns diverge. Epigenetic changes can be
maintained through life, or they can be reversed

Question 40

Causes of epigenetic factors diverging in identical twins (2)

Answer 40

1. External factors (smoking, diet, exercise) altering modification
2. Small defects in epigenetic transcription during cellular
   division over lifespan

Question 41

Are epigenetic changes heritable?

Answer 41

Most epigenetic changes to the genome are reset each generation, but some epigenetics information can be passed across generations. In female mammals, epigenetic mechanisms play a role in X chromosome inactivation:
one of the two X chromosomes is inactivated by methylating the histone protein

Question 42

Effects of maternal behavior in rats

Answer 42

Grooming behavior of mothers toward female offspring was measured. Females exposed to a greater frequency of grooming behaviors took longer to reach puberty. Females in the lower frequency group had greater LH and progesterone surges. Therefore, those from the low group were more reproductively succesful

Question 43

Sensitization

Answer 43

Increased response to a stimulus

Question 44

What is the difference between linked genes and supergenes? (2)

Answer 44

1. Supergenes are loci that are always inherited
   together. Their expression results in species
   polymorphism.
2. Linked genes that are not part of a supergene,
   are likely to be inherited together, but may be
   involved in different mechanisms. They are not
   related in terms of the phenotype they induce