6.1.2 Patterns of Inheritance

Question 1

Chi squared

Answer 1

Compare expected phenotype ratio (from the punnet table) with the observe phenotype ratio. Show whether differences are significant or due to chance.

Question 2

How to do chi squared

Answer 2

-Punnet table
- Total number of offspring/ratio total x predicted ratio
- Observed is found
- Observed - Expected
- Square numbers
- Divide numbers by the Expected results
- Add both numbers (each phenotype) together
- Use 0.05 and degrees of freedom (number of phenotypes - 1)
- If the value is higher than the critical value, reject the null hypothesis
- If the value is lower than the critical value, accept null hypothesis

Question 3

Continuous Variation

Answer 3

• Quantitative
• No distinct categories
• Polygenic
• Environmental and genetic factors
• E.g. height

Question 4

Discontinuous Variation

Answer 4

• Qualitative
• Categories
• Monogenic
• Genetic factors
• E.g. gender

Question 5

Phenotypic Variation

Answer 5

There is variation within a population.
Influenced by genotype, environment or both.

Question 6

Genotype only

Answer 6

• E.g. skin colour (continuous)
• E.g. blood group (discontinuous)

Question 7

Environmental only

Answer 7

• E.g. etiolation (plants growing spindly due to lack of sun)
• E.g. chlorosis (environmental factors cause lack of chlorosis and so yellow plants)

Question 8

Both genotype and environment

Answer 8

• E.g. height
• E.g. body mass

Question 9

Gene

Answer 9

Sequence of bases on dna molecule that codes for a functional protein which results in a characteristic.

Question 10

Allele

Answer 10

A version of a gene, you have two from each of the homologous chromosomes. B or b.

Question 11

Genotype

Answer 11

The alleles an organism has.
BB, Bb or bb.

Question 12

Phenotype

Answer 12

The characteristics produced by the genotype.

Question 13

Dominant

Answer 13

Appears in phenotype even if there’s only one copy. If B is for brown and b is blue eyes then BB and Bb would be brown.

Question 14

Recessive

Answer 14

Appears in phenotype if two are present. bb would be blue.

Question 15

Codominant

Answer 15

Alleles can both be expressed
if dominant. CR and CW can produce roan colouring in cows.

Question 16

Locus

Answer 16

Position of gene on the chromosome.

Question 17

Homozygous

Answer 17

Carries two of the same allele. BB or bb.

Question 18

Heterozygous

Answer 18

Carries one of each allele. Bb.

Question 19

Carrier

Answer 19

A person carrying an allele not expressed but present in phenotype and can be passed to offspring.

Question 20

Sex linked

Answer 20

XA, Xa or Y.

Question 21

Autosomal linkage

Answer 21

• 3:1
• Not sex chromosomes
• Same autosome are said to be linked as they’ll stay together through independent assortment
• Closer they are the more likely to be linked.

Question 22

Monogenic

Answer 22

Caused by one gene.

Question 23

Mono hybrid crosses

Answer 23

• 3:1 ratio
• One characxtaristic controlled by one gene
• NN, Nn, nn

Question 24

Polygenic

Answer 24

Caused by more than one gene.

Question 25

Dihybrid crosses

Answer 25

- 9:3:3:1 ratio - Two characteristics caused by two genes - RY, Ry, rY, ry

Question 26

Epistatic gene

Answer 26

- 9:7 - Masks the expression of another gene

Question 27

Sexual selection

Answer 27

Alleles make the individual more attractive to find a mate

Question 28

Gene flow

Answer 28

Movement of alleles through migration

Question 29

Gene pool

Answer 29

Complete range of alleles present in a population

Question 30

Natural selection

Answer 30

- Some better adapted to section pressures due to alleles - Increased chance of survival and reproduction - Pass on advantageous allele - Greater proportion of the next generation inherits allele - Frequency of allele increases

Question 31

Stabilising selection

Answer 31

Environment isn’t changing much, individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. Reduces the range of possible phenotypes. Selection pressures may act against extreme. E.g. babies survival is best if not over or underweight.

Question 32

Directional selection

Answer 32

Change in the environment and the average phenotype is no longer the best adapted. Less common organisms with extreme phenotypes are selected. Allele frequency shifts towards extreme. E.g. light moths survive best in country and dark survive best in urban so more common in each

Question 33

Disruptive selection

Answer 33

The alleles for the extremes if the phenotype range are selected for so works against the mean. E.g. birds attack intermediate plumage but leave threatening bright and non threatening dull.

Question 34

Allopathic speciation

Answer 34

Populations are prevented from breeding because they’re geographically isolated. CReates two separate species