Patterns Of Inheritance

Question 1

Define phenotype

Answer 1

The observable characteristics of an organism

Question 2

How can meiosis bring about 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, meaning they only contain half of 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 mono genetic 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 same time

Question 6

What is meant by sex-linkage ?

Answer 6

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

Question 7

What is meant by multiple alleles ?

Answer 7

A gene with more than two alleles

Question 8

What is meant by codominant alleles ?

Answer 8

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

Question 9

What is meant by autosomal linkage ?

Answer 9

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 10

What is meant by epistasis ?

Answer 10

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

Question 11

What is the chi-squared test ?

Answer 11

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

Question 12

How is the chi-squared test performed ?

Answer 12

The formula results in a number, which is then compared to a critical value (for the corresponding degrees of freedom) . If the number is greater than or equal to the critical value, we conclude there is no significant difference and the results occurred due to chance

Question 13

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

Answer 13

• Discontinuous Variations = Characteristic determined by one gene, influenced by only genetics
• Continuous variation = Characteristics determined by more than one gene, influenced by both environment and genetics

Question 14

What is stabilising selection ?

Answer 14

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

Question 15

What is directional selection ?

Answer 15

Occurs when environmental conditions change. Individuals with phenotype suited to the new conditions will survive and pass on their genes. Over many generations majority of the population have this characteristic

Question 16

What is genetic drift ?

Answer 16

A change is the populations allele frequencies that occur due to chance rather than selective pressures.

Question 17

What is meant by a genetic bottleneck ?

Answer 17

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, e.g Natural disaster

Question 18

What is meant by the founder effect ?

Answer 18

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 19

What is the Hardy-Weinberg principle ?

Answer 19

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

Question 20

Explain the Hardy-Weinberg equation for calculating allele frequency

Answer 20

The frequencies of each allele for a characteristic must add up to 1.0. The equation is: p+q=1
Where p= Frequency of dominant allele and
q= frequency of recessive allele

Question 21

Explain the Hardy-Weinberg equation for calculating genotype frequency

Answer 21

The frequencies of each genotype for a characteristic must add up to 1.0. The equation is therefore; p^2+2pq+q^2=1
Where p^2= Frequency f homozygous dominant
2pq= frequency of heterozygous, and q^2= frequency o homozygous recessive

Question 22

Define speciation

Answer 22

Where a population is split and isolated, there are different selective pressures on the two groups. If the genetic makeup changes to the extent the two groups can no longer interbreed, they have become separate species

Question 23

What is meant by allopatric speciation ?

Answer 23

Speciation resulting from a physical barrier e.g. river, mountain range. The environments occupied by two groups are different, and therefore different alleles are favoured.

Question 24

What is sympatric speciation ?

Answer 24

Speciation resulting from a non-physical barrier e.g. a mutation that no longer allows two organisms to produce fertile offspring. Any changes in anatomy or behaviour may also prevent breeding

Question 25

What is artificial selection ?

Answer 25

• Identify organisms with the desirable trait
• Cross-breed these organisms with each other
• Identify the offspring with the desirable trait
• Cross-breed these with each other and continue this over many generations
• Until all offspring have the desirable trait

Question 26

Give examples of artificial selection in plants and animails

Answer 26

• Plants = seeds used from plants that produce larger fruits and vegetables
• Animals = Cows with higher milk yield are chosen to selectively bred

Question 27

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

Answer 27

Allows any traits that were accidentally bred out to be reintroduced, or to revert back to a point before any negative traits were introduced

Question 28

Give some ethical issues around the use of artificial selection

Answer 28

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