Phenotypic ratios

Question 1

Why will ratios of phenotypes not actually be easily calculated?

Answer 1

• Independent assortment
• Linkage
• Crossing over

Question 2

Linkage

Answer 2

Genes are located on the same chromosome and inherited together as one unit

Question 3

Linked genes in non-sex chromosomes

Answer 3

Autosomal linkage

Question 4

Examples of linked characteristics in fruit flies

Answer 4

Body colour (brown and black) and wing length (long and short)
Bb and Vv

Question 5

Recombinant offspring

Answer 5

They have different combinations of alleles for linked genes than either parent due to crossing over.

Brown flies with short wings

Question 6

The closer the genes on a chromosome:

Answer 6

the less likely they are to be separated during crossing over and less recombinant offspring are likely to be produced

This is referred to as the degree of crossing over.

Question 7

Recombination frequency

Answer 7

number of recombinant offspring
———————————————-
total number of offspring

Question 8

Indication of a recombinant frequency of 50%

Answer 8

no linkage and genes are on separate chromosomes

Question 9

Indication of a recombinant frequency of less than 50%

Answer 9

There is a gene linkage and the random process of independent assortment has been hindered.

Question 10

How can recombination frequencies be used?

Answer 10

• To work out the genes on a chromosome.
  A frequency of 1% relates to a distance of one map unit on a chromosome

Question 11

Chi-squared test

Answer 11

Measures the size of the difference between the results observed and those expected to understand if differences are due to chance or a significant reason.

Question 12

E in chu-squared test

Answer 12

expected frequencies

Question 13

O in chi-squared test

Answer 13

Observed frequencies

Question 14

Chi-squared value larger than critical value

Answer 14

• There is a statistically significant difference between observed and expected results and probability shows that these are not due to chance
• Must be another reason

Question 15

Degrees of freedom chi-squared

Answer 15

Number of comparisons being made - 1

Question 16

If chi-squared value is less than critical value

Answer 16

• Not strong enough evidence to reject null hypothesis

Question 17

Epistasis

Answer 17

Interaction of genes at different loci

Question 18

How is gene regulation a form of epistasis?

Answer 18

• Regulatory genes control the activity of structural genes by binding (interacting)

Question 19

How can gene interactions occur?

Answer 19

• In biochemical pathways involving only structural genes
• Gene regulation

Question 20

How can a gene be masked?

Answer 20

• By the lack of expression of the previous gene in its pathway.
• Eg. a,b,c,d are a pathway. They all need to be expressed to produce enzymes.
• If one is inhibited, then the molecule broken down by the next enzyme is not produced.
• Lack of substrate, so expression of this gene is not observed in phenotype

Question 21

Hypostatic

Answer 21

A gene that is effected by another gene

Question 22

Epistatic

Answer 22

A gene that affects the expression of another gene.

Question 23

When two recessive alleles at a gene loci lead to the lack of an epistatic gene?

Answer 23

• This is recessive epistasis

Question 24

If a dominant allele results in an epistatic gene?

Answer 24

• Dominant epistasis

Question 25

What decides the colour of a labrador?

Answer 25

- How much melanin is deposited in the skin and fur - One gene codes for the production of melanin (dominant black and recessive brown in fur / yellow in skin) - Another gene codes for where melanin is deposited (E in skin and fur, e in skin only)

Question 26

Yellow fur in labradors

Answer 26

Recessive Epistasis