Week 1: Hereditary Flashcards
What were the 2 theories of inheritance
Blending
- 2 parents mix (blend)
Particulate
- Parents pass discrete heritable units that retain identity (alleles)
What are the 4 rules for the law of segregation?
- Alt. versions of genes account for the variations
- You inherit 2 alleles (1 from each parent)
- If alleles differ dominant is seen
- two alleles separate during gamete production
What is the typical phenotypical ratio in dihybrids?
9:3:3:1
What is the rule of multiplication?
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)
What is the rule of addition
probability of an event that can occur in 2 or more independent ways = sum of separate probabilities 1/4 + 1/4 = 1/2
Explain incomplete dominance
Both alleles are expressed + a combination is seen
Explain codominance
2 alleles alter phenotype in separate ways
What is an example of a dominant recessive relationship?
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)
What is Pleiotrophy?
Most genes do not just affect one character/ phenotype (many symptoms) e.g. sickle cell anaemia
What is Epistasis?
More than 1 allele involved in phenotype (work together in a process) e.g. hair colour and baldness
What is an example of Polygenic inheritance?
Human skin colour (determined by 3 genes)