Patterns of inheritance 6.2 Flashcards
1
Q
What is interspecific variation?
A
Variation between different species
2
Q
What is intraspecific variation?
A
Variation between individuals of the same species
3
Q
What is an allele?
A
Different versions of the same gene
4
Q
What is a phenotype?
A
Physical characteristics of an organism resulting from the genotype
5
Q
What is a genotype?
A
A description of the alleles carried by an organism
6
Q
What does polygenic mean?
A
Controlled by multiple genes
7
Q
What does monogenic mean?
A
Controlled by one or few genes
8
Q
What is continuous variation?
A
Where the genetic variation between individuals in a population shows a range with a smooth gradient and many intermediates
9
Q
What are the characteristics of continuous variation?
A
- quantitative
- controlled by multiple genes and the environment
- line graph
Eg/ Height, length of stalk
10
Q
What is discontinuous variation?
A
Where pheotype classes are distinct and discrete with very few or no intermediates between phenotypes
11
Q
What are the characteristics of discontinuous variation?
A
- qualitative
- controlled by single or few genes
- no intermediates
- bar chart
Eg/ blood types, gender
12
Q
What are the two factors that affect phenotypic variation?
A
Genetic and environmental
13
Q
What are genetic factors that cause phenotypic variation?
A
- gene mutations
- chromosome mutations
- sexual reproduction
14
Q
How do gene mutations cause phenotypic variation?
A
- mutagens increase the rate of mutations
- can occur during gamete formation
- can be presistent where they are transmitted through many generations without change
- can be random where the are not directed
15
Q
What are mutagens?
A
Physical and chemical agents that increase the rate of mutation
16
Q
How do chromosome mutations cause phenotypic variation?
A
- may occur during meiosis
- could be deletion, inversion, translocation, duplication or non-disjunction
17
Q
What does non-disjunction mean?
A
- when spindle fibres fail to separate chromatids during meiosis, resulting in gametes with an extra chromosome
- shows in two forms: aneuploidy and polyploidy
18
Q
What are aneuploidy and polyploidy?
A
- aneuploidy = the chromosome number is not an exact multiple of the haploid number for the organism (down syndrome)
- polyploidy = multiple copies of a full set of chromosomes (haploid + diploid = triploid)
19
Q
What are environmental factors that affect phenotypic variation?
A
- diet
- climate
- lifestyle
- light
- minerals
20
Q
What are specific examples of environment affecting phenoypic variation in humans and plants?
A
- speaking in a regional accent
- having a scar following an injury
- etiolation - plants growing abnormally long and spindly due to lack of light
- chlorosis - plants not producing enough chlorophyll due to lack of magnesium
21
Q
How does sexual reproduction lead to genetic variation within a specie?
A
- during sexual reproduction, genetic variation is caused by the result of new combinations of alleles in a gamete or individual
- caused by crossing over during prophase one of meiosis
- independent assortment of homologous chromosomes during metaphase 1
- independent assortment of sister chromatids in metaphase 2
- random fusion of gametes during fertilisation
22
Q
What does locus mean?
A
The location of the gene
23
Q
What is a monogenic characteristic?
A
A characteristic that is controlled by one gene with two distinct alleles
24
Q
What is the ratio for a monohybrid cross where both parents are heterozygous?
A
- 3:1
-1:2:1
25
What does codominance mean?
When both alleles are expressed and neither one is recessive
26
What is a dihybrid characteristics?
When there are two different genes being passed down each with different alleles that show the inheritance two different characteristics in an individual
27
What is the phenotypic ratio for a dihybrid cross where both parents are heterozygous?
9:3:3:1
28
What is meant by multiple alleles in inheritance?
More than two alleles are needed for a single gene
(blood types)
29
When is inheritance said to be sex linked?
When the gene is only carried on one sex chromosome and not the other
(the sex of an individual affects what alleles they pass onto their offspring)
30
Why are recessive conditions more likely to show in men?
They only have one X chromosome so they are much more likely to show sex linked recessive conditions
(colour blindness and haemophilia)
31
What are autosomes?
Any chromosome which is not a sex chromosome
32
What is autosomal linkage?
When genes which are located on the same chromosome stay together in the original parental combination
33
What kind of cross do you use for autosomal likage?
A dihybrid cross
34
What are the expected ratios of autosomal linkage?
Large amounts of the original parental genotypes
35
What would the gametes be for these parents if they are linked? TGtg X tgtg
- (TG) (tg)
- (tg)
36
When does epistasis occur?
When two genes on different chromosomes affect the same feature
(one gene affects the expression of another gene)
37
What ratios can you expect when epistasis is taking place?
- 12:3:1 (dominant epistasis)
- 13:3 (dominant epistasis)
- 9:3:4 (recessive epistasis)
- 9:7 (recessive epistasis)
38
What is dominant epistasis?
A dominant allele at one gene locus masks the expression of the alleles at a second gene locus
39
What is recessive epistasis?
Two recessive alleles at one gene locus masks the expression of the alleles at a second gene locus
40
What does chi squared measure?
It compares the observed values to the expected values to determin whether the difference between the observed and expected values is significant
41
What happens if the results are below the critical value on a chi squared test?
- accept null hypothesis
- any difference is due to chance and not significant
- probability that it is due to chance is abover 5%
42
What happens if the results are above the critical value on a chi squared test?
- reject null hypothesis
- difference is significant and not due to chance
- probability that it is due to chance is below 5%
43
What is stabilising selection?
- no factor has changed
- alleles for extreme phenotypes are selected against
- natural selection leads to constancy in the population where intermediate phenotypes are favoured
- reduces allele frequency which reduces genetic diversity
44
What is directional selection?
- a factor has changed (selection pressure)
- natural selection which favours a new phenotype
- results in a change of allele frequency and individuals are favoured in one direction
45
What is the genetic bottleneck?
When a large number of a population die and then the size of the population increases again
46
What is the effect of the genetic bottleneck?
- genetic diversity decreases
- may be loss of advantageous alleles or a disproportionate frequency of harmful alleles
- could improve the gene pool whilst shrinking genetic diversity
47
What is the founder effect?
When a new population is established by a very small number of individuals who originated from a larger parent population
48
What is the effect of the founder effect?
- loss of genetic diversity
- migrated population might not be fully representative of the parent population
- reduction in the gene pool
49
What is genetic drift?
- gradual change in allele frequencies in a small population due to chance and not natural selection
- if a population is small chance can affect which alleles are passed on to the next generation
- in large populations it is less likely to have an effect because any chance variations in allele frequencies usually even out
- over time some alleles can be lost or favoured purely by chance
50
What is occuring when gradual change in allele frequencies in a small population is due to chance and not natural selection?
Genetic drift
51
What does the Hardy-Weinberg principle calculate?
Allele frequencies in populations
52
What does q stand for in the Hardy-Weinberg principle?
The total number of homozygous recessive alleles
53
What does p stand for in the Hardy-Weinberg principle?
The total number of homozygous dominant alleles
54
What does 2pq stand for in the Hardy-Weinberg principle?
The total number of heterozygous alleles
55
What is a species?
A group of organisms that interbreed to produce fertile offspring
56
What is speciation?
- development of a new species
- occurs when populations of the same species become reproductively isolated
57
What is allopatric speciation?
- it is speciation that occurs as a result of geographical isolation
- stops gene flow
- experience different selection pressures
- causes changes in the gene pool (allele frequencies)
- leads to changes in phenotypes
- form separate species
58
How might a species be reproductively isolated?
- morphology - genitals no longer match
- differences in courtship rituals
- difference in mating seasons
59
What is sympatric speciation?
- rapid genetic change
- speciation that takes place with no geographical barrier where two populations live in the same place but there is no gene flow between them
- ecological separation (difference in soil pH)
- behavioural separation (difference in eating)
60
What is artificial selection?
- the process of choosing organisms with desirable traits and selectively breeding them together to enhance the expression of these desirable traits over time
- known as selective breeding
- knowledge of the alleles causing the traits is not needed as individuals are selected by their phenotype not genotype
- desireable traits can sometimes negatively affect the organisms health
61
What are the uses of artificial selection?
- cows with higher yeild of milk or meat
- chickens that lay large eggs
- domesstic dogs with gentle nature
- sheep with good quality wool
- disease resistant crop
- higher crop yeild
- better tasting fruit
62
Why is it important to maintain a resource of genetic material in wild types of organisms?
- reduces inbreeding depression
- increases hybrid vigour
63
What are the ethical issues with the use of artificial selection?
- selective breeding can lead to inbreeding
- organisms are closely related to eachother
- reduces the gene pool and number of alleles in the population
- organisms inherit harmful genetic defects
- organisms are vulnerable to new diseases
- some processes have rsulted in conditions and diseases which are harmul to the animals involved
64
What is complimentary epistasis and what is the ratio?
The presence of a particular allele at each locus is required for the expression of a particular phenotype (9:7)
