Chapter 20- Patterns of Inheritance and Variation

Question 2

Define the genotype

Answer 2

The combination of alleles an organism inherits for a characteristic

Question 3

Define the phenotype

Answer 3

The observable characteristics of an organism

Question 4

What are the two factors that have the biggest impact on variation?

Answer 4

Genetics and environment can both cause variation

Question 5

What is chlorosis?

Answer 5

A genetic condition in plants where the cells can’t produce enough chlorophyll- however mostly displays because of environmental conditions
-Lack of light
-Mineral deficiency
-Virus infections

Question 6

What are modifications in terms of genetics?

Answer 6

Any changes the environment makes to a persons phenotype- these are not inheritable traits

Question 7

Describe the difference between discontinuous and continuous variation

Answer 7

Continuous- the variable falls on a spectrum between two extremes
Discontinuous- the variable falls into one of several defined groups

Question 8

What causes continuous variation?

Answer 8

Polygenes- characteristics controlled by more than one gene

Question 9

What are we showing when we talk about monogenic inheritance?

Answer 9

Investigating the role of a singular gene- eg pea colour as famously investigated by Gregor Mendel

Question 10

When does codominace occur?

Answer 10

When two dominant genes are expressed simultaneously (eg red and white pigments coding for pink flowers)

Question 11

Give an example of codominance in animals

Answer 11

Blood group,
a combination of either I(a) I(b) or I(o)
I(a) and I(b) are codominant but I(o) is recessive to both
Different combinations result in different crosses

Question 12

What does it mean if a gene is sex linked?

Answer 12

Because the Y chromosome is smaller than the X chromosome, males only have one copy of certain genes. If these genes are recessive, they are more likely to appear in the phenotype, so there are characteristics that occur more frequently in males

Question 13

Give an example of a sex linked genetic disorder

Answer 13

Haemophilia- blood that clots extremely slowly due to the absence of a protein blood clotting factor

Question 14

What does a dihybrid cross show?

Answer 14

The inheritance of two genes

Question 15

Define autosomal linkage

Answer 15

When linked genes are found on different pairs of chromosomes

Question 16

Why are linked genes important?

Answer 16

They are inherited together as one unit- no independent assortment unless the alleles are separated by chiasmata

Question 17

What is the recombination frequency and how do we calculate it?

Answer 17

A measure of the amount of crossing over that has happened during mitosis

Recombination frequency = number of recombinant offspring / total number of offspring

Question 18

Define recombinant offfspring

Answer 18

A different combination of alleles than either parent

Question 19

What result of recombination frequency indicates there is no linkage between two characteristics?

Answer 19

50%

Question 20

What does the Chi-squared test measure for?

Answer 20

A statistical test that measures the size of the difference between the observed results and the expected results

Question 22

What do large results of a Chi-squared test mean?

Answer 22

There is a statistically significant difference between the observed and expected results

Question 23

Define epistasis

Answer 23

The interaction of genes at different loci

Question 24

How do genes mask other genes?

Answer 24

If a certain gene is not expressed as expected, it can block other genes in it’s biochemical pathway, and therefore masking the effects of the genes that came before it

Question 25

What do we call a gene that has been affected by another gene?

Answer 25

Hypostatic

Question 26

When does dominant epistatis occur?

Answer 26

If a dominant allele results in gene having an effect on another gene

Question 27

Define the gene pool

Answer 27

The sum of all the genes present in a population at any given time

Question 28

Define allele frequency

Answer 28

The relative frequency of a particular allele in a population Allele frequency always equates to p + q = 1 where p is A and q is a

Question 29

What can be used to calculate allele frequency?

Answer 29

The Hardy-Weinberg principle- in a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution

Question 30

How is the Hardy Weinberg principle expressed?

Answer 30

p*2 +2pq + q*2 = 1 p*2 = frequency of homozygous dominant genotype 2pq= frequency of heterozygous dominant genotype q*2 = frequency of homozygous recessive genotype

Question 31

Why is the Hardy Weinberg principle not applicable to real life situations?

Answer 31

Because almost no populations exist that are not effected by external factors, random mating and no mutation

Question 32

Name the 5 factors often effecting evolution

Answer 32

Mutation Sexual selection Gene flow Genetic drift Natural Selection

Question 33

Define gene flow

Answer 33

the movement of alleles between small populations- immigration and emigration changes allele frequency

Question 34

Why are smaller populations less likely to adapt to new environments?

Answer 34

Reduced gene pool, reduced genetic biodiversity means that natural selection doesn’t occur well and many in the population die

Question 35

Define a population bottleneck

Answer 35

A large reduction in population size for at least one generation

Question 36

What is an advantage of a population bottleneck?

Answer 36

The beneficial mutation will quickly become very common and lead to the survival of the species

Question 37

Define the founder effect

Answer 37

When small populations arise due to the establishment of new colonies of isolated individuals- any rare alleles randomly present in these individuals will become very common eg Ellis van Creld syndrome in the Amish

Question 38

What shape will the distribution of different variants show if plotted on a graph?

Answer 38

The bell shaped curve- normal distribution

Question 39

What is directional selection?

Answer 39

Occurs when there is a change in environment and the most common phenotype is no longer the most advantageous, shifting allele frequency towards extreme phenotypes

Question 40

Define disruptive selection

Answer 40

When extremes are selected for and the norm is selected against , eg finches in the Galápagos Islands

Question 41

Define speciation

Answer 41

The formation of a new species through the process of evolution

Question 42

What are the events leading up to speciation?

Answer 42

Members of a population are isolated and no longer interbreed, reducing gene flow Alleles in both groups undergo random mutation, as the environment of each group changes Accumulation of mutation and allele frequencies eventually changes the normal phenotype Members of each group are so different they can’t produce fertile offspring

Question 43

Define allopatric speciation

Answer 43

When populations are separated by a physical barrier like a river or a sea. Seperation of a smaller group leads to the founder effect and genetic drift occurring

Question 44

Define sympatric speciation

Answer 44

Occurs most frequently in plants, when members of different species interbreed and produce fertile offspring eg the loganberry. The offspring can’t breed back into either of the original populations, stopping gene flow

Question 45

Give an example of allopatric speciation

Answer 45

In 1995 15 iguanas survived a hurricane in the Caribbean but reached a different island to their original population- this could be the start of allopatric speciation

Question 46

Give an example of sympatric speciation

Question 47

Define the term polymorphic

Answer 47

Display more than one visible phenotype for certain characteristics

Question 48

What do we call the allele that codes for the most common phenotype?

Answer 48

The wild allele