4: Mendelian Genetics

Question 1

What model organism did Mendel use for his experiments? Explain why

Answer 1

→ Good system to work with to study inheritance
Comes in a wide variety of phenotypes (shapes & colours) → caused by a single gene
Short gen time, large no. of progeny
Usually self-pollinating
Easy to manipulate (cross)
It’s said he grew more than 33,500 pea plants over the 7 years

Question 2

Describe Mendel’s process of pea cross pollination

Answer 2

1) Anthers removed before they shed pollen

2) Transfer pollen from another plant to another plant

3) = cross pollination

Question 3

Define filial

Answer 3

Relating to sons/daughters

Question 4

Describe Mendel’s first cross & the ratio found

Answer 4

White flower plant X purple flower
= all F1 progeny purple flower

F1 = 1st filial (sons/daughters)

F1 X F1
= ratio of 3.15:1 in F2

Question 5

What was the ratio in Mendel’s F2 progeny?

Answer 5

always around 3:1

Question 6

What were Mendel’s 4 conclusions from his experiments?

Answer 6

Alternative versions of a gene cause variation → called alleles
An organism inherits 2 alleles, one from each parent
Alleles may be dominant or recessive
Alleles segregate at random during gamete production

Question 7

Describe Mendel’s 1st Law: the principle of segregation

Answer 7

the principle of segregation
→ 2 members of a gene pair, segregate from each other during gamete formation
→ each half of the gametes carry 1 member of the pair
Consistent with the ‘particulate’ mechanism (particulates = genes)
Before this, people believed in the ‘blending’ hypothesis

Question 8

Describe blending hypothesis

Answer 8

Mixing paint analogy for genes e.g blue x yellow = green
Results in uniform pop.

= early idea, now obviously incorrect

Question 9

What is the null hypothesis for Mendel’s 1st law test cross?

Answer 9

Homozygote (ww, white) X heterozygote (Pw, purple) = equal no. of purple and white flowered plants (1:1 ratio)

Question 10

Describe Mendel’s 2nd law of independent assortment

Answer 10

→ The alleles of different genes segregate independently of each other
There are exceptions: 2 genes close to each other on the same chromosome do not assort independently

Question 11

Describe Mendel’s test cross for his 2nd law

Answer 11

→ looking at 2 different phenotypes at once (seed colour and shape)
Yellow, round X green, wrinkled
Expected F2 ratio:
Y:G = 3:1
R:W = 3:1
9:3:3:1