Patterns of inheritance

Question 1

genotype

Answer 1

the genetic make up of an organism

Question 2

phenotype

Answer 2

the observable characteristics of an organism

Question 3

environmental variation in plants

Answer 3

chlorosis: caused by lack of light, mineral deficiencies and viral infection

Question 4

environmental variation in animals

Answer 4

body mass: caused by poor diet and exercise

Question 5

causes of genetic variation

Answer 5

random gamete fusion at fertilisation

Question 6

dominant allele

Answer 6

allele always expressed if present

Question 7

recessive allele

Answer 7

allele only expressed if 2 are present

Question 8

homozygous

Answer 8

2 identical alleles for a phenotype

Question 9

heterozygous

Answer 9

2 different alleles for a phenotype

Question 10

about continuous variation

Answer 10

• takes any value within a given range
• genetic and environmental variation
• caused by polygenes

Question 11

about discontinuous variation

Answer 11

• specific values
• genetic variation
• caused by 1 or 2 genes

Question 12

co-dominance

Answer 12

both alleles for a gene are equally dominant and can form an intermediate phenotype

Question 13

multiple alleles

Answer 13

genes that have more than 2 alleles but only 2 can be present in an organism eg. blood group

Question 14

sex-linkage

Answer 14

Y chromosome smaller than X chromosome. X chromosome contains more genes that males only carry one copy of - recessive phenotypes more common eg. haemophilia

Question 15

Autosomal linkage

Answer 15

alleles on the same (non-sex) chromosome are inherited together
genes cant form as many combination

Question 16

autosomal linkage: recombinants

Answer 16

offspring that have different allele combinations to parents due to crossing over

Question 17

recombination frequency

Answer 17

(recominant offspring/total offspring) x100

50% - no linkage
<50% - linkage

Question 18

epistasis

Answer 18

the alleles of one gene (epistatic) affect/ mask the expression of another gene (hypostatic) in the phenotype

Question 19

recessive epistasis

Answer 19

the recessive allele of a gene causes epistasis

Question 20

dominant epistasis

Answer 20

the dominant allele of a gene causes epistasis

Question 21

allele frequency formula

Answer 21

p + q = 1

p = frequency of A
q = frequency of a

Question 22

hardy-weinberg formula

Answer 22

p^2 + 2pq + q^2 = 1

p^2 = frequency of AA
2pq = frequency of Aa
q^2 = frequency of aa

Question 23

hardy weinberg principle assumptions

Answer 23

• population is large and isolated
• random mating
• no mutation
• no selection pressures

Question 24

stabilising selection

Answer 24

individuals with the average phenotype in a population benefit from natural selection

Question 25

directional selection

Answer 25

an event such as a sudden change in environment means that individuals with less common/ more extreme phenotypes benefit from natural selection

Question 26

genetic drift

Answer 26

a change in allele frequency of an existing allele in a population due to chance

Question 27

founder effect

Answer 27

small population arises due to the formation of new colonies by isolated individuals

Question 28

genetic bottleneck

Answer 28

a sudden decrease in population size and genetic variation

Question 29

speciation

Answer 29

the formation of new species by evolution

Question 30

allopatric speciation

Answer 30

members of the same population become separated by a physical barrier - different selection pressure and different adaptations

Question 31

sympatric speciation

Answer 31

members of 2 different species interbreed to form fertile offspring the hybrid is a new species