L4 Geographic distribution

Question 1

What are hybrid zones?

Answer 1

Where genetically distinct populations meet, mate and reproduce

Question 2

What is polyploidy speciation?

Answer 2

When a new individual has a different number of chromosomes than its parents, so cannot mate with parent group

Question 3

Why are hybrids good to study when understanding speciation?

Answer 3

Involved in nearly all speciation events and have a range of genotypes that the different selection pressures that separate the taxa

Question 4

What is a cline?

Answer 4

Change in the frequency of an allele from one geographical point to another

Question 5

How do European hedgehogs exhibit hybridisation?

Answer 5

Two main species, originated during the ice age when populations were isolated, then moved out of refugee after ice retreated, populations were isolated for a significant amount of time, and hybrid zones occur where the groups cross over

Question 6

What are the different consequences for hybrid zones?

Answer 6

indefinite
merge
become reproductively isolated
Third species evolves

Question 7

How may hybrid zones be indefinite?

Answer 7

Two different populations remain, some interaction occurring in the hybrid zone, all remain the same

Question 8

Why may hybrid zones merge?

Answer 8

Populations may join up across a hybrid zone if there is no detriment to the fitness of either population and interbreeding is high

Question 9

When does reproductive isolation occur?

Answer 9

If hybrids are unfit with interbreeding then selection will act to keep the two populations apart.

Question 10

What shape is the cline when populations are not interacting?

Answer 10

Get a steep, or stepped cline

Question 11

What does a cline with lots of gene flow look like?

Answer 11

Shallow

Question 12

What cline characteristics can we use to tell us about the mixing of populations?

Answer 12

Shape
co-occurence
movement

Question 13

What controls the shape of the cline?

Answer 13

Dispersal and how much selection is acting on the alleles

Question 14

What happens as dispersal increases?

Answer 14

Cline gets shallower

Question 15

What is an example of a wide cline?

Answer 15

Blood groups in humans - AB/B has the B allele, which occurs at a low frequency. Was brought up through Europe with the Roman Empire, covers an entire continent so has a very shallow slope

Question 16

What happens if selection is acting on alleles?

Answer 16

One allele is more likely to survive in each environment, and selection will act to keep it that way. Strength of selection depends own the strength of the allele

Question 17

What does the cline look like under strong selection?

Answer 17

Steep

Question 18

What is heterozygote disadvantage?

Answer 18

Disadvantage to be heterozygote, have a reduced fitness

Question 19

What is a tension zone?

Answer 19

High selection against hybrids where there are two homozygous populations, and heterozygotes are less fit. Hybrid numbers will be kept down

Question 20

What does the cline in a tension zone look like?

Answer 20

Steep

Question 21

Give an example of a tension zone

Answer 21

Rock pocket mice Two different morphs, black and beige, living on two different sand types. Are under high predation pressure Mutation caused in 4 different amino acids . Selection acts to keep the morphs in the correct environments, would struggle to survive in opposite coloured sand

Question 22

What is a primary hybrid zone?

Answer 22

Natural selection alters alleles in a continuous population Covers a vast amount of area and changes alleles seen depending on the environment. Different clines are seen across the transect

Question 23

What is a secondary hybrid zone?

Answer 23

Species that spent a significant amount of time being allopatric move out of refugee and meet again - all clines happen at that one point.

Question 24

What did the study into hybridisation in the horse mouse show?

Answer 24

Looked at 105 sites in 1800 mice, at allonym sites, that they assumed were neutral, and at x linked site, which were assumed to be under selection. Found a strong barrier to gene flow, with a steep cline. Even neutral alleles are influenced by selection in the esteem

Question 25

How can you distinguish between a primary and secondary hybrid zone?

Answer 25

Primary hybrid zone occurs when environmental change causes an allele increase, happens across an area. Secondary occurs when separated, and even neutral allies are affected

Question 26

What are allozymes?

Answer 26

Different forms of enzymes that do the same job

Question 27

What is an example of a primary hybrid zone?

Answer 27

Mussels in Long Island sound and surrounding area, Sea is salty and pulls water out of the cells. Mussels have to adapt around it - Remove an amino acid, which helps retain salt and waters. As salinity increases across the sound, more individuals with this allele occur

Question 28

What is cline asymmetry?

Answer 28

When cline doesn’t move in different directions at the same rate

Question 29

What is backcrossing?

Answer 29

Mating of a hybrid with one of its parents or an organism with the same genetic characteristics as one of the parents.

Question 30

What is introgression?

Answer 30

The movement of genes from one species or population to another, by hybridisation and backcrossing - alleles move into another population

Question 31

What are the consequences of indefinite hybridisation?

Answer 31

Selection can maintain steep clones at some loci, could be a tension zone. Tends to remain only if character differences are favoured by different environments. May be subject to change, will exist in the areas of low density

Question 32

What are the consequences of merging hybrid zones?

Answer 32

Occurs when fitness of hybrid isn’t lower that original populations, so introgression leads to breakdown of post zygotic reproductive barriers. Variation and distinction between the two populations is lost.

Question 33

What are the consequences of reproductive isolation in hybrid zones?

Answer 33

Strengthens barriers to gene exchange, so large areas of the genome are protected from introgression,