6.1.2 Patterns of Inheritance

Question 1

Define phenotype

Answer 1

The expression of an organism’s genetic constitution e.g. ginger hair combined with the environment e.g. diet

Question 2

How can meiosis bring genetic variation ?

Answer 2

*Random arrangement of chromosomes during lining up
*Crossing over of chromatids before the first division.

Question 3

How does random fertilisation bring about genetic variation ?

Answer 3

*Gametes are haploid cells, meaning they only contain half a persons DNA
*As this is determined by meiosis, every gamete contains different DNA
*Therefore the same two individuals can produce genetically different offspring.

Question 4

Define monogenic inheritance

Answer 4

Where one phenotypic characteristic is controlled by a single gene

Question 5

Define dihybrid inheritance

Answer 5

Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time

Question 5

What is meant by sex linkage ?

Answer 5

Where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual

Question 6

What is meant by multiple alleles?

Answer 6

A gene with more than two alleles (such as blood type)

Question 7

What is meant by codominant alleles ?

Answer 7

Two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together.

Question 8

What is meant by autosomal linkage

Answer 8

•Where two or more genes are located on the same (non-sex) chromosome
•In this case, only one homologous pair is needed for all four alleles to be present
•For genes that aren’t linked, two homologous pairs are needed.

Question 9

What is meant by epistasis ?

Answer 9

Where two non-linked genes interact, with one gene either masking or suppressing the other gene

Question 10

What is the chi squared test ?

Answer 10

•A statistical test to find out whether the difference between observed and expected data is due to change or real effect
•Can be used to compare expected phenotypic ratios with observed ratios.

Question 11

How is chi-squared test result interpreted ?

Answer 11

•The formula results in a number, which is the compared to a critical value for its corresponding degree of freedom
•If the number is greater than or equal to the critical value, we conclude there is no significant difference and the results are due to chance.

Question 12

How can the number of genes coding for a characteristic influence variation ?

Answer 12

•Discontinuous variation - characteristic determined by one gene (monogenic inheritance)
•Continuous variation - characteristic determined by more than one gene (polygenic inheritance).

Question 13

What is stabilising selection ?

Answer 13

•Occurs when environmental conditions stay the same
•Individuals closest to the mean are favoured, and any new characteristics are selected against
•Results in low diversity

Question 14

What is directional selection ?

Answer 14

•Occurs when environmental conditions change
•Individuals with phenotype suited to the new conditions will survive and pass on their genes
•Over time the mean of the population will move towards these characteristics.

Question 15

What is genetic drift ?

Answer 15

•A change in a populations allele frequencies that occurs due to chance rather than selective pressure
•In other words, it is caused by ‘sampling error” when selecting alleles for the next generation.

Question 16

What is meant by a genetic bottleneck ?

Answer 16

Where a catastrophic event dramatically reduces the size of a population, thereby decreasing the variety of alleles in the gene pool and causing large changes in allele frequencies.

Question 17

What is meant by the founder effect ?

Answer 17

When a small number of individuals become isolated, forming a new population with a limited gene pool, with allele frequencies not reflective of the original population.

Question 18

What is the Hardy-Weinberg principle ?

Answer 18

Allows us to estimate the frequency of alleles in a population, as well if allele frequency is changing over time

Question 19

Explain the Hardy-Weinberg equation for calculating allele frequency

Answer 19

•The frequencies of each allele for a characteristic must add up 1.0
•The equation is therefore p+q=1.

Question 20

What do p and q represent in the Hardy-Weinberg equation for allele frequency ?

Answer 20

•p = dominant allele frequency
•q = recessive allele frequency.

Question 21

Explain the Hardy-Weinberg equation for calculating genotype frequency

Answer 21

•The frequencies of each gene o type for a characteristic must add up to 1.0
•The equation is p²+2pq+q²=1
•pq is the frequency of heterozygous.

Question 22

Define speciation

Answer 22

*Where a population is split and isolated, resulting in different selection pressures on the two groups
*If the genetic makeup change to the extent the two groups can no longer interbreed, they become separate species.

Question 23

What is meant by allopatric speciation ?

Answer 23

•Speciation resulting from a physical barrier e.g. river or road
•The environments occupied by the two groups are different and therefore different alleles are favoured.

Question 24

What is meant by sympatric speciation ?

Answer 24

Speciation resulting from a non-physical barrier e.g. a change in anatomy or behaviour that prevents breeding

Question 25

What is artificial selection ?

Answer 25

When humans choose particular organisms to breed together in order to produce a desired characteristic in the offspring

Question 26

Give an example of artificial selection in plants and animals

Answer 26

•Plants - seeds from plants that produce larger yields are preferred
•Animals - cows with a higher milk yield are chosen and bred.

Question 27

Why is it important to keep a recourse of genetic material when selective breeding ?

Answer 27

Allows any traits that were accidentally bred out to be reintroduced, or to revert to before any negative traits were added

Question 28

Give some ethical issues surrounding artificial selection

Answer 28

•Anatomical changes in animals e.g. respiratory issues in pugs
•Higher susceptibility to disease in both plants and humans.