PATTERNS OF INHERITANCE

Question 1

phenotypic variation

Answer 1

differences between the phenotypes of a group of organisms

Question 2

environmental factors affecting phenotypic variation in animals & plants

Answer 2

• diet in animals affects body mass
• etiolation in plants due to lack of light (grow long and spindly to reach light source)

Question 3

genetic factors affecting phenotypic variation in plants & animals

Answer 3

• genes affecting body mass
• chlorosis where plant doesn’t produce enough chlorophyll due to iron deficiency

Question 4

how does sexual reproduction lead to genetic variation?

Answer 4

• crossing over in prophase 1
• independent assortment in metaphase 1 due to random distribution and segregation of homologous chromosomes
• independent assortment in metaphase 2 due to random distribution and segregation of sister chromatids
• random fertilisation

Question 5

what do monogenic inheritance diagrams show?

Answer 5

inheritance of alleles of a single gene

Question 6

what is the F1 outcome for monogenic inheritance?

Answer 6

100%

Question 7

what do dihybrid crosses show?

Answer 7

the inheritance of 2 separate genes on different chromosomes eg pea colour & shape

Question 8

in a heterozygous dihybrid cross what will the ratio be?

Answer 8

9:3:3:1

Question 9

what are multiple alleles?

Answer 9

genes with more than 2 alleles eg IA and IB for blood group

Question 10

what is codominance?

Answer 10

both alleles equally dominant so both expressed in phenotype

Question 11

what is sex linkage?

Answer 11

traits inherited by 1 biological sex
- determined by non homologous (only present on X) region of X
- tops of Y chromosomes lost in evolution so it has less genes

Question 12

what is linkage?

Answer 12

genes for different characteristics are found at different loci on the same chromosome
- inherited together

Question 13

what is epistasis?

Answer 13

• genes at 1 locus interact with genes at another
• by masking or suppressing their expression

Question 14

what is autosomal linkage?

Answer 14

• 2 genes on same chromosome
• inherited together

Question 15

what is the ratio for recessive epistasis?

Answer 15

9:7 or 9:3:4

Question 16

what is the ratio for dominant epistasis?

Answer 16

12:3:1 or 13:3

Question 17

what is the ratio for reciprocal epistasis?

Answer 17

15:1

Question 18

what is the purpose of a chi squared test?

Answer 18

assesses whether results are different from expected due to chance or another factor

Question 19

when does a chi squared value show results are significant?

Answer 19

if the calculated value is greater than the critical value

Question 20

continuous variation

Answer 20

• any value on a scale
• caused by genes with many alleles
• eg height
• shown on histogram

Question 21

discontinuous variation

Answer 21

• distinct categories
• caused by genes with few alleles and the environment
• eg blood group
• shown on bar chart

Question 22

stabilising selection

Answer 22

• eliminates extremes in a population
• favours most normal/common
• occurs with unchanging environmental conditions

Question 23

genetic drift

Answer 23

• random change in allele frequency in a population
• some alleles passed and some disappear
• some phenotypes become common and others rare

Question 24

founder effect

Answer 24

• loss of genetic variation
• establishment of new population as a small number of individuals colonise a new area

Question 25

directional selection

Answer 25

- favours individuals at the extreme - changes population characteristics - occurs due to environmental change

Question 26

genetic bottleneck

Answer 26

- chance event - causes a dramatic reduction in the size of a population/gene pool - big effect on allele frequency

Question 27

speciation

Answer 27

evolution of a new species from an existing one

Question 28

sympatric speciation

Answer 28

- reproductive mechanisms with no physical barrier - change in courting behaviour which is not recognised by the rest of the species - polyploidy (mutation affecting whole sets of chromosomes) - hybrid sterility (mating of 2 species)

Question 29

allopatric speciation

Answer 29

- geographical isolation - 2 populations of same species separated - selection of diff alleles - mutations & diff selection pressures - gene pools become so different that they are reproductively isolated

Question 30

artificial selection

Answer 30

- selective breeding of desired characteristics - repeated over generations - eg to increase milk or wheat yield - important to maintain a resource of genetic material for use in selective breeding as growing conditions change - important to consider ethics surrounding extreme selective breeding

Question 31

under what assumptions is the hardy Weinberg principle used?

Answer 31

- large population - mating in population is random - no mutations, genetic drift or migration - no selective advantages

Question 32

what does p represent in the HW equation?

Answer 32

frequency of dominant allele

Question 33

what does q represent in the HW equation?

Answer 33

frequency of recessive allele

Question 34

what does pq represent in the HW equation?

Answer 34

frequency of heterozygotes