17 Mendelian Genetics

Question 1

How are peas cross pollinated?

Answer 1

Anthers removed before they shed pollen
Transfer pollen to another plant

Question 2

What was Mendel’s first cross?

Answer 2

Purple plant crossed with white plant
- All progeny were purple

Question 3

What is the ratio for F2 progeny?

Answer 3

3:1

Question 4

What did Mendel conclude from his data?

Answer 4

1) Alternative versions of a gene cause variation - alleles
2) An organism inherits two alleles, one from each parent
3) Alleles may be dominant or recessive
4) Alleles segregate during gamete production

Question 5

What is Mendel’s first law?

Answer 5

The principle of segregation:
The two members of a gene pair segregate from each other during the formation of gametes. Half of the gametes carry one member of the pair, and the other half carry the other member of the pair

Question 6

What did people believe prior to Mendel?

Answer 6

‘Blending’ hypothesis
Results in a uniform population

Mendel’s data consistent with ‘particulate’ mechanism
- parents pass on discrete heritable units - genes

Question 7

What is the testcross?

Answer 7

Cross a heterozygote to an individual that is homozygous for the recessive allele
Result - equal number of purple and white-flowered plants

Question 8

What is the ratio of seed colour against seed shape?

Answer 8

9:3:3:1
RY:RG:WY:WG

Shows the characters are acting independently of each other

Question 9

What is Mendel’s second law?

Answer 9

The principle of independent assortment
The alleles of different genes segregate independently of each other
Exceptions:
Linked genes

Question 10

Which testcross proves Mendel’s second law?

Answer 10

Cross parent heterozygous for both characters with parent homozygous recessive for both characters
1:1:1:1

Question 11

When was Mendel’s work published?

Answer 11

1865

Question 12

Who rediscovered Mendel’s work?

Answer 12

1900
Hugo de Vries
Carl Correns
Erich von Tschermack

Question 13

How was Mendel’s work criticised?

Answer 13

Fisher (1936)
- Mendel’s ratios were always very close to theoretical expectations given sample sizes
- Very low probability of getting this degree of occurrence
- Fisher attributed the alleged forgery to an unknown assistant

Question 14

Why is Mendelian inheritance important?

Answer 14

Important for evolution by natural selection
Blending inheritance would cause all individuals to be the same