6.1.2 Patterns of Inheritance Flashcards
1
Q
what are the two types of variation
A
continuous and discontinuous
2
Q
what is continuous variation
A
when individuals in a population vary within a range, there are no distinct categories
3
Q
what are examples of continuous variation
A
- height
- waist circumference
- fur length
- leaf surface area
4
Q
what is discontinuous variation
A
when there are two or more distinct categories, and each individual falls into only one of these categories, with no intermediates
5
Q
what are examples of discontinuous variation
A
- blood group
- violet flower colour
6
Q
what two things can influence variation
A
genetics
environment
or both
7
Q
what makes up the different genotypes of organisms
A
- different species have different genes
- individuals of the same species have the same genes, but different versions of them (alleles)
- the genes and alleles make up genotype
8
Q
how does sexual reproduction lead to variation in a species
A
- meiosis makes gametes with a unique assortment of alleles
- due to crossing over
- and independent assortment of alleles
- random fusion of gametes during fertilisation
- increases genetic variation in the offspring
9
Q
what is phenotypic variation, and give a human example
A
- the variation in phenotypes of organisms
- caused by the difference in genotypes
- e.g. human blood groups, which have 3 different blood group alleles, and 4 different blood groups
10
Q
how many genes code for inherited characteristics that show continuous variation
A
- many genes
- said to be polygenic
- e.g. human skin colour is said to be polygenic, as comes in loads of different shades
11
Q
how many genes code for inherited characteristics that show discontinuous characteristics
A
- usually influenced by only one, or a small number of genes
- said to be monogenic
- e.g. violet flower colour, either purple or white
12
Q
how does the environment influence variation
A
- caused by differences in the environment
- e.g. climate, food lifestyle
- characteristics controlled by the environment CHANGE over an organism’s life
13
Q
what are examples of environmental factors affecting variation
A
- etiolation: when plants grow abnormally long and spindly because they’re not getting enough light
- chlorosis: when plants don’t produce enough chlorophyll and turn yellow, caused by several environmental factors, e.g. lack of magnesium in the soil
- diet: in animals
14
Q
what are the differences in genetic and environmental factors
A
genetic: determine the genotype and characteristics the organism is BORN with
environmental: influence how some of these characteristics develop
15
Q
what is most phenotypic variation influenced by
A
- combination of BOTH factors
- usually showing continuous variation
16
Q
what are examples of variation being caused by both environmental and genetic factors
A
1) height of pea plants: pea plants come in tall and dwarf forms (discontinuous variation) but the exact height of tall and dwarf varieties varies (continuous variation) due to environmental factors (e.g. light intensity and water availability affecting how tall plant grows)
2) body mass in animals: partly genetic, but strongly influenced by environmental factors, such as diet. e.g. if your diet doesn’t include right nutrients, body mass is likely to be lower than determined by genes. continuous variation
17
Q
what is a gene
A
a sequence of bases on a DNA molecule that codes for a protein, which results in a characteristic
18
Q
what is an allele
A
a different version of a gene
- most plants and animals have 2 versions of each gene, one from mom and one from dad
- represented using letters, e.g. B and b
- order of bases in each allele is slightly different, coding for different versions of the same characteristic
19
Q
what is genotype
A
the alleles an organism has, e.g. Bb
20
Q
what is phenotype
A
the characteristics alleles produce, e.g. brown eyes
21
Q
what is dominant
A
22
Q
what is recessive
A
23
Q
what is codominant
A
24
Q
what is locus
A
the fixed position of a gene on a chromosome
- alleles of a gene are found at the same locus on each chromosome in a pair
25
what is homozygote
an organism that carries two copies of the same allele
26
what is heterozygote
an organism that carries two different alleles, Bb
27
what is a carrier
a person carrying an allele that is not expressed in the phenotype but that can be passed on to offspring
28
for each gene, how many alleles does a person have
2
29
what contains only one allele for each gene
gammetes
30
what are genetic diagrams used for
predicting the phenotypes and genotypes of offspring if two parents are crossed
31
what is monogenic inheritance
inheritance of a characteristic controlled by a single gene
32
what do monogenic crosses show
the likelihood of different alleles of a gene being inherited by offspring of particular parents
33
what is the first and second set of offspring called
the F₁ and F₂ generations
34
how would you do a punnett square for a normal, monogenic cross
1) list the parental phenotypes
2) list the parental genotypes
3) list the gametes from them
4) cross them in 4x4 grid
5) list the phenotypic ratios of the offspring
35
what does it mean when alleles show codominance
both alleles are expressed in the phenotype, as neither is recessive
36
explain codominance in reference to sickle cell anaemia
- those with HOMOzygous for normal haemoglobin, HᴺHᴺ, don't have the disease
- those HETEROzygous for haemoglobin, HᴺHᶻ have a sickle-cell trait, meaning they have a bit of both sickle-cell and normal haemoglobin
- those HOMOzygous for sickle-cell haemoglobin HᶻHᶻ, have sickle-cell anaemia, so all of their blood cells are sickle-shaped
37
what does multiple alleles mean
when there are more than 2 alleles of the same gene
38
explain multiple alleles in terms of blood groups
Io = recessive O blood group
IA = dominant A blood group
IB = dominant B blood group
- blood groups A and B are codominant, so people with IAIB with have blood group AB
- IoIA= A blood group
- IoIB= B blood group
39
what is dihybrid inheritance
40
what do dihybrid crosses show you
41
what is phenotypic ratio
the ratio of the different phenotypes in offspring
42
what are some common phenotypic ratios
43
why may you not get the expected phenotypic ratio
- sex linkage
- autosomal linkage
- epistasis
44
sex-linkage
45
what does autosome mean
any chromosome that isn't a sex chromosome
46
what does autosomal genes mean
genes located on autosomes
47
why are genes on the same autosome linked
- if they are on the same chromosome
- they will stay together during the independent assortment of chromosomes, and their alleles will be passed onto their offspring together
- only reason this won't occur is if crossing over splits them up
48
which genes are more likely to be linked on an autosome
the closer together the two genes, the more likely they are said to be linked
- because crossing over is less likely to split them up
49
why does linkage alter phenotypic ratios
- in a dihybrid cross, you can expect a 9:3:3:1 ratio
- BUT, it is more likely to be like a monohybrid ratio of 3:1
- as the two autosomally-linked alleles are inherited together
- so a higher proportion of offspring will have their parents' (heterozygous) genotypes
50
what is epistasis
where the allele of one gene masks the expression of the alleles of other genes
51
what can you predict would be the phenotypic ratio of recessive epistasis
9:3:4
52
what can you predict would be the phenotypic ratio of dominant epistasis
12:3:1
53
what is chi-squared
54
what is always the null hypothesis in a chi-squared test
there is no significant difference between the observed and expected results
55
what is chi squared formula
56
what is the critical value you use for chi-squared
5% probability that results are due to chance only
- corresponding to degree of freedom (n-1)
57
what does chi-squared tell you compared to critical value
- if value greater than CV, reject Ho
- if the value is smaller than CV, accept Ho
58
what is gene pool
the complete range of alleles present in a population
59
how are new alleles generated
mutations in genes
60
what is gene frequency
how often an allele occurs in a population
61
what is evolution in terms of genes and alleles
the frequency of an allele in population changing over time
62
explain how evolution occurs through natural selection
- individuals in a population vary because they have different alleles (new alleles are usually generated through mutation or meiosis)
- selection pressures create a struggle for survival
- some individuals are better adapted to selection pressures than others
- individuals with advantageous alleles, which increase chance of survival, are more likely to survive, reproduce and pass on their advantageous allele than individuals with different alleles
- so greater proportion of the next generation inherit the advantageous allele
- so again, more likely to survive, reproduce and pass on allele
- the frequency of the advantageous allele increases generation to generation
63
what is stabilising selection
in a stable environment, those with characteristics in the middle of the range are more likely to survive, e.g. fur length
64
what is directional selection
when there is a change in the environemnt, individuals with alleles at an extrememe are more likely to survive and repordue
65
what is another way, other than natural selection, that evolution can occur
genetic drift
66
what is genetic drift
where instead of environmental factors affecting which individuals survive and reproduce, chance dictates which alleles are passed on
67
how does genetic drift work
- individuals in a population show variation in phenotypes
- by chance, the allele for one genotype is passed onto offspring more than others
- the number of individuals with the allele increases
- if by chance the same allele is passed on more often again and again, it can lead to evolution as it becomes more common
68
does natural selection or genetic drift affect the evolution of a population more
- work alongside each other
- but in SMALLER POPULATIONS: genetic drift had a greater effect as chance has a greater influence (in larger populations, any variation in allele frequency usually evens out across total population)
69
how is human blood groups good example of genetic drift
- tribes were found in isolated, smaller groups
- blood groups doesn't effect chances of survival or reproduction
70
what is a genetic bottleneck
an event, such as a natural disaster, that causes a big reduction in population size, leading to reduction in gene pool
71
what is an example of a genetic bottleneck effecting genetic drift
- mice can be either black or grey, and colour doesn't impact their survival
- natural disaster leaves only one black mouse and rest grey mice
- grey becomes common colour due to genetic drift
72
what is the founder effect
what happens when a few organisms from a population start a new population and there are only a small number of alleles in the initial gene pool
73
explain the founder effect
74
what is the Hardy-Weinberg principle
predicts that frequencies of alleles in a population won't change from one generation to the next
75
under what conditions is the Hardy-Weinberg principle true
- large population
- no immigration
- emigration
- mutations
- natural selection
- random mating
76
what are the hardy weiberg equations
p+q=1
p = frequency of dominant allele
q = frequency of recessive allele
p2+2pq+q2=1
p2= frequency of homo dom. genotype
2pq= frequency of hetero genotype
q2= frequency of homo rec. genotype
77
what is a species
a group of similar organisms that can reproduce to give fertile offspring
78
