Week 1: Hereditary

Question 1

What were the 2 theories of inheritance

Answer 1

Blending
- 2 parents mix (blend)
Particulate
- Parents pass discrete heritable units that retain identity (alleles)

Question 2

What are the 4 rules for the law of segregation?

Answer 2

1. Alt. versions of genes account for the variations
2. You inherit 2 alleles (1 from each parent)
3. If alleles differ dominant is seen
4. two alleles separate during gamete production

Question 3

What is the typical phenotypical ratio in dihybrids?

Answer 3

9:3:3:1

Question 4

What is the rule of multiplication?

Answer 4

Probability of a compound event is equal to product of separate probabilities of independent single events
e.g. 1/2 x 1/2 = 1/4 (coin toss)

Question 5

What is the rule of addition

Answer 5

probability of an event that can occur in 2 or more independent ways = sum of separate probabilities 1/4 + 1/4 = 1/2

Question 6

Explain incomplete dominance

Answer 6

Both alleles are expressed + a combination is seen

Question 7

Explain codominance

Answer 7

2 alleles alter phenotype in separate ways

Question 8

What is an example of a dominant recessive relationship?

Answer 8

Tay-Sachs Disease

• Brain cells can’t metabolise gangliosides (faulty enzyme)
• Only homozygotes have disease (recessive)
• Hetrozygotes have intermediate phenotype (not complete disease): half the amount of enzyme needed (incomplete dominance)

Question 9

What is Pleiotrophy?

Answer 9

Most genes do not just affect one character/ phenotype (many symptoms) e.g. sickle cell anaemia

Question 10

What is Epistasis?

Answer 10

More than 1 allele involved in phenotype (work together in a process) e.g. hair colour and baldness

Question 11

What is an example of Polygenic inheritance?

Answer 11

Human skin colour (determined by 3 genes)