Inheritance

Question 1

What is Mendel’s experimental approach? Why did he chose _____ plant?

Answer 1

• Use characteristics which can provide quantitative results.
• Chose to work with peas because:
o Many varieties e.g. colour & height.
o Short life cycle.
o Large number of offspring.
o Mating can be strictly controlled by removing young stamen to stop self-pollination.
• Crossing F1  F2. Mendel usually followed traits for PF1F2 generations.

Question 2

What is true breeding?

Answer 2

• over many generations of self-pollination produces only the same variety as the parent plant (homozygous) – P generation (parent).

Question 3

What is Hybridisation? What is a monohybrid? What is a dihybrid?

Answer 3

• cross of two pure breeding varieties. First gen hybrid = F1 (first filial generation).
• Cross following only one trait = monohybrid/ two traits = dihybrid.

Question 4

What is a Test cross? What do you draw to determine this?

Answer 4

• If an unknown genotype is found it can be crossed with a known homozygous genotype expressing recessive (white) trait. A Punnett square is then used to predict the possible outcomes.
• The results are then matched to the Punnett square possible outcomes to determine the mystery parent genotype.

Question 5

What is the Law of independent assortment?

Answer 5

• Two or more genes assort independently – each pair of alleles segregates independently of each other pair of alleles, during gamete formation.
• This only applies to genes located on different chromosomes that are not homologous. Or very far apart on the same chromosome.

Question 6

What is Pure breeding? What can you conclude from this?

Answer 6

• P x W  F1= 1:1:1:1 F2 = P3:1W

o Conclude: recessive trait was not destroyed or blended in F1 just masked by presence of dominant purple trait.

Question 7

What is Independent assortment? What can you conclude from this?

Answer 7

• cross of two true breeding plants: YYRR x yyrr  F1=YyRr  F2= phenotypic ratio of 9:3:3:1.
  o Conclude alleles for each gene segregate independently of the other genes.

Question 8

What is Incomplete dominance? What can you conclude from this?

Answer 8

• neither alleles are completely dominant. E.g. two colours mixing in presence of both alleles. = 1:2:1.
  o Due to neither allele being dominant lower and upper is replace with C +superscript e.g. CW for white CR for red.

Question 9

What is Codominance?

Answer 9

both alleles are dominant – both phenotypes show but not as a mixed intermediate but as two distinct phenotypes on the heterozygote.

Question 10

What is Epistasis?

Answer 10

gene on one locus alters that on a different locus – 9:3:4.

Question 11

What is it called when a gene is located on a sex chromosome? What can this lead to?

Answer 11

• Sex linkage

• Can lead to diseases of only one gender.

Question 12

Sketch the chromosomal basis of mendels laws.

Answer 12

See pic in your notes.