6.2 Patterns of Inheritance Flashcards
1
Q
Define genotype
A
genetic makeup of an organism
2
Q
Define phenotype
A
visible characteristics of an organism
3
Q
What contributes to phenotypic variation?
A
Environmental and genetic factors
4
Q
Environmental examples of factors affecting phenotypic variation
A
diet in animals and etiolation or chlorosis in plants
5
Q
What is etiolation?
A
When plants grow in places with insufficient light
6
Q
What is chlorosis?
A
Where leaves produce insufficient chlorophyll due to dim light or soil with insufficient magnesium
7
Q
How can sexual reproduction lead to genetic variation within a species?
A
- Meiosis- allele shuffling in prophase 1
- independant assortment of chromosomes in meta/anaphase 1
- independent assortment of chromatids in meta/anaphase 2
- Random fusion of gametes - any can combine
8
Q
What is monogenetic inheritance?
A
the inheritance of a characteristic controlled by a single gene
9
Q
Define allele
A
Version of a gene
10
Q
Define heterozygous
A
not true-breeding; having different alleles at a particular gene locus on a pair of homologous chromosomes
11
Q
Define homozygous
A
true-breeding; having identical alleles at a particular gene locus on a pair of homologous chromosomes
12
Q
Define dihybrid
A
involving two gene loci
13
Q
What is independent assortment?
A
the alleles of two or more different genes get sorted into gametes independently of one another
14
Q
What happens when two heterozygous dihybrids are crossed?
A
You get a 9:3:3:1 ratio.
15
Q
Define codominance
A
where both alleles present in the genotype of a heterozygous individual contribute to the individuals phenotype
16
Q
Define multiple alleles
A
characteristic for which there are three of more alleles in the populations gene pool
17
Q
Define sex-linked
A
gene present on (one of) the sex chromosomes
18
Q
What are autosomes?
A
All chromosomes apart from sex chromosomes
19
Q
What is specific about autosomal pairs?
A
they are all completely homologous
20
Q
Why are sex chromosomes not fully homologous?
A
XX and XY are different
21
Q
Examples of sex-linked characteristics
A
colour blindness and haemophilia A
22
Q
What is autosomal linkage?
A
gene loci present on the same autosome that are often inherited together
23
Q
Why are linked genes likely to be passed on together?
A
Because their loci are close together on the chromosome
24
Q
Examples of genetic factors that affect variation
A
- gene mutations
- chromosome mutations
- sexual reproduction
25
Examples of how gene mutations lead to variation
- Physical agents (x-rays, gamma, UV)
- Chemical agents (benzopyrene, mustard gas, nitrous acid, aromatic amines)
- Biological agents (some viruses, trasponsons, food contaminants such as mycotoxins, alcohol)
26
What are transposons?
'jumping genes'
| remnants of viral nucleic acid that have been incorporated into our genomes
27
Examples of chromosome mutations
- deletion
- inversion
- translocation (one piece of chromosome breaks off and attaches to another part)
- duplication
- non-disjunction (one pair of chromosomes fails to separate, leaving one gamete with an extra chromosome)
- aneuploidy
- polyploidy
28
Describe aneuploidy
chromosome number is not exact multiple of haploid number
29
Describe polyploidy
where you have an extra set of chromosomes
30
What is monogenic?
determined by a single gene
31
Why did Mendel use pea plants?
- easy to grow
| - can be cross fertilised
32
What is a test cross?
You test the plants that youve been given with a known strain
33
Define dihybrid
involving two gene loci
34
Ratio dihybrid unlinked
9:3:3:1
35
What do we assume in dihybrid inheritance?
- genes on separate chromosomes
| - genes inherited independently
36
What are males for X linked genes?
hemizygous
37
What is X inactivation
mechanism that prevents expression of twice the number of X-linked genes than males
- in every female cell nucleus, one X chromosome inactivated
- X chromosome which is inactivated is chosen at random
38
Why are only female cats tortoiseshell?
-inactivation of X chromosomes so random between orange and black pigment expression
39
Ratio of autosomally linked genes with no crossing over
3:1
40
If the gene loci are further apart on the chromosome, does it increase or decrease the chance of recombinant alleles forming?
There is a greater chance of recombinant alleles forming when they are further apart on a chromosome
41
Define epistasis
interaction of non-linked gene loci where one masks the expression of the other
42
If alleles at the first locus are epistatic to those at the second locus, what are those at the second locus to those at the first?
hypostatic
43
Describe recessive epistasis
the homozygous presence of a recessive allele prevents the expression of another allele at the second locus
44
Do genes have to be linked or non-linked for recessive epistasis?
Non-linked, found on two different chromosomes
45
Example of recessive epistasis
Colour of salvia flower
46
Example of dominant epistasis
feather colour in chickens
47
Ratio of dominant epistasis
13: 3
12: 3:1
48
Ratio of recessive epistasis
9:3:4
49
Example of complementary genes
Coat colour in mice
50
Define crossing over
the reciprocal exchange of parts of chromatids between homologous chromosomes
51
If you see a pathway, what is it likely to be?
epistasis
52
If you see alleles of genes written with superscript, what is it most likely to be?
codominance
53
What ratio indicates complementary gene action?
9: 7
9: 3:4
9: 3:3:1
54
What is the chi squared test?
statistical test designed to find out if the difference between observed and expected data is significant or due to chance
55
Null hypothesis for chi squared test
There is no statistically significant difference between the observed and expected data. Any difference is due to chance
56
When can we use chi squared?
- data are in categories and are not continuous
- strong biological theory to predict expected values
- large sample size
- data are in raw counts (cant be ratios/ percentages)
- no zero scores in raw count data
57
What happens when the chi squared value is less than the critical value?
difference is due to chance
not significant
accept null hypothesis
58
What happens when the chi squared value is more than the critical value?
the difference is statistically significant
| we reject the null hypothesis
59
What is continuous variation?
variation that produces phenotypic variation where the quantitative traits vary by very small amounts between one group and the next
60
What is discontinuous variation?
genetic variation producing discrete phenotypes - two or more non-overlapping categories
61
What are characteristics that exhibit discontinuous variation controlled by?
alleles of a single gene locus
| monogenic
62
What is continuous variation determined by?
polygenic, many genes
63
What happens to the range of characteristics when you increase the number of gene loci in continuous variation?
greater range of characteristics
64
What happens when discontinuous variation is not monogenic?
different loci have large and DIFFERING effects on phenotype
65
What is directional selection?
type of natural selection that occurs when an environmental change favours a new phenotype and so results in a change in the population mean
66
What is the founder effect?
when a small sample of an original population establishes in a new area; its gene pool is not as diverse as that of the parent population
67
What is a genetic bottleneck?
a sharp reduction in size of a population due to environmental catastrophes such as earthquakes, floods, disease or human activities such as habitat destruction, overhunting or genocide, which reduces genetic diversity. As the population expands it is less genetically diverse than before.
68
What is stabilising selection?
- natural selection leading to constancy withing a population
- intermediate phenotypes are favoured and extreme selected against
- reduces genetic variation
69
Three types of selection
- stabilising
- directional
- destructive
70
Example of stabilising selection
Birth mass of babies
71
When does genetic drift arise?
after a genetic bottleneck or as a result of the founder effect
72
Define population
members of a species, living in the same place and at the same time, that can interbreed
73
Factors affecting allele frequencies within populations
- population size
- mutation rate
- migration
- natural selection
- changes to environment
- isolation
- non-random mating
- genetic drift
- gene flow
74
What does the Hardy Weinberg principle assume?
- population large enough to make sampling error negligible
- mating is random
- no selective advantages
- no mutation, migration or genetic drift
75
What is p in Hardy-Weinberg?
frequency of dominant allele
76
What is q in Hardy-Weinberg?
frequency of recessive allele
77
Define allopatric speciation
formation of two different species from one original species, due to geographical isolation
78
Define sympatric speciation
formation of two different species from one original species, due to reproductive isolation, while the populations inhabit the same geographical location
79
Define speciation
the splitting of a genetically similar population into two or more populations that undergo genetic differentiation and eventually reproductive isolation, leading to the evolution of two or more species
80
What are the two types of isolating mechanism?
geographical and reproductive
81
What leads to reproductive isolation?
biological and behavioural changes
82
Examples of biological changes that can lead to isolation
MUTATION=
-changing foraging behaviour or enabling to exploit new niche (diurnal cannot breed with nocturnal)
CHANGE IN CHROMOSOME NUMBER =
-prevent gamete fusion
-make zygotes less viable
-infertile hybrid offspring
-CHANGES IN ANIMAL GENITALIA/ PLANT FLOWER STRUCTURE
83
Examples of behavioural changes that lead to isolation
change in courtship behaviour
84
What is artificial selection?
selective breeding of organisms: involves humans choosing the desired phenotypes and interbreeding those phenotypes individually, therefore selecting the genotypes that contribute to the gene pool of the next generation of these organisms
85
Examples of animals being artificially selected
- cattle (milk, meat, leather)
- sheep and goats (wool and meat)
- horses (transport, racing military)
- pigs (meat)
- pigeons (flight capacity, plumage)
- poultry
- dogs
- cat
86
Examples of plants being artificially selected
cereal (wheat, barley, maize,millet), rice, fruit and veg
87
What are plants artificially selected for?
```
yield
short maturation time
pest resistance
infection
frost
drought
flooding and wind
improved flavour
```
88
What inbreeding depression?
if related individuals are crossed
| increased chance of inheriting harmful allele
89
What is hybrid vigour?
two individuals of different varieties crossed
| individuals are heterozygous at many different gene loci
90
How can breeders increase hybrid vigour?
outcross cultivated varieties with varieties like their WILD ancestors
91
Ethical considerations of artificial selection
- domesticated animals retain juvenile characteristics so they cant defend themselves and become easy prey
- livestock have more meat and less fat = victims of low temp in winter
