Lecture 36

Question 1

How long does it take for a mutation to reduce allele frequency from 1c to 0.5?

Answer 1

-The number of generations to reduce the allele frequency from 1.0 to 0.5 is 69 314 generations, assume ~ 25 years per generation = 25 X 69 314 = 1 732 850 years
-but it can set up the source of the new alleles in the population
can put the individual at an advantage or disadvantage

Question 2

Is population size significant for allele frequencies?

Answer 2

-yes it can be

Question 3

What is genetic drift?

Answer 3

-• random changes in allele frequencies due to sampling error
• occurs in all populations but effect pronounced in small populations:
-in a small population can see the effect whereas the big pop will dampen the results
-often some alleles are lost ins mall populations due to chance

Question 4

What are the two types of genetic drift?

Answer 4

• Founder effect : small group from a larger population settle in a new location
• the allele frequency may not represent the original population, by chance
• Bottleneck: population goes through a severe reduction and only a few members survive to produce next generations.
• after a disaster, the surviving individuals don’t represent the population before the disaster

Question 5

What is the bottleneck effect?

Answer 5

large popualtin-disaster- then fewer alleles

Question 6

What are the 4 examples of founder effect?

Answer 6

• 1. Pingelap atoll – founder effect
• 2. Huntington Disease and Tasmania – founder effect
• 3. Tristan d’Cunha – founder effect/bottleneck
• 4. Dunkers and Amish – founder effect

Question 7

What is the modern synthetic theory of evolution?

Answer 7

-

Question 8

What are species?

Answer 8

-Members of a species share a common gene pool Different species have separate gene pools
Speciation - separation of gene pools
forces which are pushing allele frequencies apart are greater than the forces holding allele frequencies constant

Question 9

What is allopatric speciation?

Answer 9

• physical barrier separates gene pools

- river/roadway… separates them into subgroups, if separated for long enough= speciation!

Question 10

What is sympatric speciation?

Answer 10

-separation of gene pools occurs in the
same area
-one subset of the population separated in the same area
-due to chromosomal changes, can’t interbreed!
-often Sympatric separated by chromosome number
-one group produces halpid gametes, the other produces diploid gametes= lot of abnormalities

Question 11

What is reproductive isolation (5)?

Answer 11

-Prezygotic mechanisms:
prevent fertilisation and zygote formation
1. Habitat : geographic or ecological isolation
2. Seasonal or temporal
3. Ethological
4. Mechanical
5. Physiological

Question 12

What is reproductive isolation- in case-Habitat : geographic or ecological isolation?

Answer 12

• squirrels on either side of the grand canyon

- can’t get to each other

Question 13

What is reproductive isolation- in case-Seasonal or temporal?

Answer 13

• things are kept apart due to seasonal or temporal= never reproductively active at the same time
• orchids

Question 14

What is reproductive isolation- in case-Ethological?

Answer 14

-ethological= behavioural
-different bird dances in different species= to mate!
-courtship -malehighsteps
• frog calls •c ricketsongs • bird plumage
-forg calls= have to match otherwise won’t mate
= so when the song changes they won’t mate! just because of the call!

drosphila= has to flap wings and running around, time spent in each is important= won’t mate

Question 15

What is reproductive isolation- in case-mechanical?

Answer 15

-differences in size

dogs= small and big can’t reach though they are the same species!

Question 16

What is reproductive isolation–physiological?

Answer 16

• Gametes make it to female but do not survive 1. spermicide in vagina
• hostile mucus in vagina= sperm killed= in some humans

Question 17

What are the post zygotic mechanisms?

Answer 17

Fertilization occurs and hybrid zygotes are formed:

1. Hybrid inviability or breakdown
2. Developmental hybrid sterility
3. F2 breakdown

-get zygote, but the offspring don’t develop and if they do they are infertile

Question 18

What is .Hybrid inviability or breakdown?

Answer 18

• Hybrid fails to develop or dies soon after birth
• get zygote but embryo dies after a few cell divisions
• dies at gastrula stage

Question 19

What is F2 breakdown?

Answer 19

– F1 hybrid forms and is fertile F2 zygote dies
-the egg and sperm get there but outcome is infertile offspring
sometimes F1 fertile but F2 zygote dies!
so the members of the same species can produce fertile offspring over a long period of time