Lecture 4

Question 0

What is Overdominance and heterosis?

Answer 0

Overdominance is the increase in a characteristic in hybrids
Heterosis is Overdominance that gives greater biological fitness (the ability to survive log enough to reproduce and produce fertile offspring)

Question 1

Only receiving one allele ie. Sex linked is known as what genetic state?

Answer 1

Hemizygous

Question 2

What is a hybrid?

Answer 2

Offspring of parents who differ genetically

Question 3

What two mechanisms give greater fitness I’m hybrids?

Answer 3

Hybrid vigour and heterozygous advantage

Question 4

What produces weakness or hybrid vigour?

Answer 4

Inbreeding - breeding in small gene pool
- can weaken strain
- partners often related giving more chance of showing recessive traits
Outbreeding - different breeds are crossed
- hybrids can have advantages taken from both breeds
- probably due to getting dominant traits of each parent

Question 5

If an f1 generation was AaBbCcDdEeFfGgHh what is the chances that a gamete would be ABCDEFGH and what are the chances of an f2 offspring being AABBCCDDEEFFGGHH?

Answer 5

Gamete = 1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 x 1/2 = 1/256

Perfect offspring = 1/256 x 1/256 = 1/65536

Question 6

Effects of outbreeding and inbreeding?

Answer 6

Outbreeding - crossing pure strains produces mongrels, sturdier animals. Pure breds have defects

Inbreeding - recessive traits cause problems, village idiot (has several recessive traits

Question 7

What is heterozygous advantage?

Answer 7

Both alleles have different advantages
Being heterozygous gives advantage of both alleles
Over time frequency of alleles come to an equilibrium eg: sickle cell trait, phenylketonuria and cystic fibrosis

Question 8

What are the effects of homozygous normal haemoglobin, homozygous sickle cell haemoglobin and heterozygous normal and sickle cell?

Answer 8

Homozygous normal - no SCD (sickle cell disease), sensitive to malaria
Homozygous SC - full SCD, resistant to malaria
Heterozygous - little or no SCD, resistant to malaria

Question 9

What are polygenic traits?

Answer 9

Characteristics that are controlled by more than 1 gene eg skin colour and eye colour

Question 10

What are the genes that cod for eye colour?

Answer 10

bey 2 - brown/blue
gey - green/blue
bey 1 - central brown

Question 11

What is the mutation known as in which a person can have two different eye colours and how is this possible?

Answer 11

Heterochromia iridium - trauma, inherited trait, drugs

Question 12

What 2 pigments cause variation in skin and hair colour?

Answer 12

Eumelamins and pheomelanins

Question 13

What genes are involved in human hair and skin colour?

Answer 13

Tyr, TyrP1, TyrP2, MC1R, Matp and P

All show incomplete dominance