6.1.2 - patterns of inheritance

Question 1

phenotypic variation

Answer 1

the variation between observable characteristics of an organism

Question 2

example of variation through a combination of genetic and environmental factors

Answer 2

• plants have green leaves because their genes code for chlorophyll, however chlorosis may make the leaves yellow through lack of ions
• body mass is affected by genetics but also hugely influenced by diet

Question 3

discontinuous variation

Answer 3

qualitative differences between phenotypes that have distincitive groups (e.g blood groups)
- caused by one gene
- genetic factors

Question 4

continuous variation

Answer 4

quantitative differenced between phenotypes where there is a large range of variation within a population (e.g height)
- caused by lots of genes (polygenic)
- environmental factors

Question 5

how does meiosis lead to genetic variation?

Answer 5

• crossing over in prophase I
• independent assortment - metaphase I and II
• random mutations
• the random fusion of gametes at fertilisation

Question 6

stabilising selection

Answer 6

• eliminates extremes in a population
• favours the most normal or common individuals
• occurs with unchanging environmental conditions

Question 7

directional selection

Answer 7

• favours individuals at the extreme in a range of variation
• changes characteristics of a population
• occurs due to a change in the environment

Question 8

genetic drift

Answer 8

the random change in allele frequency in a population, some alleles are passed on and some disappear.

Question 9

genetic bottleneck

Answer 9

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

Question 10

founder effect

Answer 10

the loss of genetic variation due to the establishment of a new population by a very small number of individuals from a much larger population.

Question 11

speciation

Answer 11

evolution of a new species from an existing one

Question 12

sympatric speciation

Answer 12

speciation from reproductive isolation mechanism with no physical barrier

Question 13

examples of sympatric speciation

Answer 13

• a change in courting behaviour
• polyploidy (mutation affecting whole sets of chromosomes)
• hybrid sterility ( a species formed from mating of two species is reproductively isolated if it is sterile)

Question 14

allopatric speciation

Answer 14

speciation from geographical barriers, such as oceans, rivers, mountains and deserts

Question 15

process of allopatric speciation

Answer 15

two populations of the same species are isolated for a time they may experience different environmental conditions
this will lead to the selection of different alleles in the two populations
gene pools become to different that if they are ever reunited, they would not be able to successfully breed together

Question 16

chi squared test

Answer 16

used to compare observed results from genetic crosses with the predicted outcomes

Question 17

what does it mean if the value of chi squared is smaller than the critical value?

Answer 17

then the difference between the observed and expected data is not statistically significant

Question 18

assumptions made when using the Hardy-Weinburg principle

Answer 18

• large population
• random mating
• no mutation, genetic drift, migration
• no selective advantage for any genotype

Question 19

hardy weinburg principle

Answer 19

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

Question 20

artificial selection

Answer 20

humans select organisms with desired characteristics and allow them to breed together.
this is repeated over many generations
this influences the evolution of a population over time

Question 21

inbreeding

Answer 21

breeding of closely related individuals

Question 22

problems caused by inbreeding

Answer 22

• limiting the gene pool reduces the chance of organisms evolving and adapting to changes in the environment
• more chance of being affected by recessive genetic disorders due to being so closely related

Question 23

monogenetic crosses

Answer 23

investigate the inheritance of alleles of a single gene.

Question 24

dihybrid crosses

Answer 24

investigate the inheritance of two separate genes on different chromosomes

Question 25

epistasis

Answer 25

genes at one locus interact with genes at another locus by masking or supressing their expression

Question 26

ratios for epistasis

Answer 26

recessive - 9:3:4 / 9:7 dominant - 12:3:1 / 13:1

Question 27

linkage

Answer 27

occurs when genes for different characteristics found at different loci on the same chromosome sre inherited together

Question 28

sex linkage

Answer 28

occurs when the genes are on the sex chromosomes, X and Y

Question 29

why can men not be carriers of sex linked diseases?

Answer 29

they only have one X chromsome so cannot by heterozygous - they either have the disease or they do not

Question 30

autosomal linkage

Answer 30

occurs when the genes are on the same chromosome - inherited together

Question 31

codominance

Answer 31

both alleles are expressed in a phenotype of a heterozygote

Question 32

allele

Answer 32

a form of a gene

Question 33

why does autosomal linkage reduce variation?

Answer 33

pairs of alleles are inherited together

Question 34

arguments against artificial selection

Answer 34

- inbreeding depression - organisms may be less biologically fit, and have significant health problems - organisms may have a shorter lifespan - organisms may be less able to reproduce

Question 35

responses to arguments against artificial selection

Answer 35

- gene banks can be used to reduce inbreeding risks, producing hybrid vigour - genetic profilling of breeding individuals can reduce risks - people may argue that domesticated animals are well cared for - benefits to society may outweigh disadvantages (e.g greater yields of milk or meat)

Question 36

why may be it be inappropiate to use the hardy weinburg principle to estimate allele frequencies in some investigatons

Answer 36

- if population is not subject to speciation - if the population is too small

Question 37

why is sexual reproduction of bacteria more likely to happen in the winter?

Answer 37

cold conditions - not optimum for offspring

Question 38

how do the combined effects of meisosis and fertilisation ensure that the same parents can have highly varied offspring

Answer 38

- crossing over of homologous chromosomes, during prophase 1 (chromosomes swap genetic material) - independent assortment oh homologoous chromosomes during metaphase/anaphase 1 - again in metaphase and anaphase II - random fertilisation of egg cell by a sperm cell to create a zygote