Module 6.2 - Patterns Of Inheritance

Question 1

Define sex linkage

Answer 1

When a gene is present on one of the sex chromosomes

Question 2

Define autosomal linkage

Answer 2

When 2 or mor genes on the same chromosome are inherited together
They do not undergo independent assortment (metaphase 1)

Question 3

Ratios

Answer 3

3:1 for two genes - autosomal linked and no crossing over

Non 9:3:3:1 with 4 phenotypes for 2 genes - autosomal linked with crossing over

Question 4

Define phenotype

Answer 4

Appearance of a characteristic

Question 5

Define genotype

Answer 5

Genetic makeup of an organism (influences phenotype)

Question 6

Continuous variation

Answer 6

No defined categories/distinct groups
Range - any value is possible
Polygenic (caused by more than one gene)
Often caused by environment
Quantitative

Question 7

Discontinuous variation

Answer 7

Defined categories
Monogenic (caused by one gene)
Genes at different loci may interact to influence one characteristic and cause discontinuous variation (epistasis)
No/very little environmental effects cause it
Qualitative

Question 8

Define deletion

Answer 8

Part of a chromosome is lost

Question 9

Define inversion

Answer 9

Section of a chromosome breaks off and rotates 180° and then rejoins
Genes still present but may be too far from regulatory genes to be expressed

Question 10

Define translocation

Answer 10

Section of one chromosome breaks off and attaches to another chromosome
May interfere with regulatory genes

Question 11

Define duplication

Answer 11

A piece of a chromosome may be duplicated causing over expression of the gene

Question 12

Define non-disjuntion

Answer 12

One pair of chromosomes or chromatids fail to separate during meiosis generating gametes with an extra chromosome

Question 13

Conditions for Hardy Weinberg

Answer 13

Large population
Random mating
No selective advantage for any genotype
No gene mutation, migration or genetic drift

Question 14

What is stabilising selection?

Answer 14

Occurs when organisms’ environment doesn’t change
Favours intermediate phenotypes over extremes
Reduces variation in a population

Question 15

What is directional selection?

Answer 15

Occurs when environment changes
Favours a new/extreme phenotype
Causes a change in population mean phenotype

Question 16

Define genetic drift

Answer 16

Random changes in allele frequency in small populations

Question 17

Why does genetic drift happen in small populations?

Answer 17

Each individual forms a larger proportion of the gene pool and therefore has a greater effect on the gene pool
It is all easier to ‘lose’ a gene from a small gene pool

Question 18

Describe genetic bottleneck (genetic drift)

Answer 18

An event rapidly reduces the numbers of a population
Some alleles are lost from the population at random
Genetic variation is reduced

Question 19

Describe the founder effect

Answer 19

Small number of individuals from an original larger population establish a new population
Some alleles are lost from the population at random
Genetic variation reduced

Question 20

Define speciation

Answer 20

The splitting of a population into 2 isolated populations that over time undergo genetic changes which result in reproductive isolation and therefore the formation of two different species

Question 21

Geographical isolation

Answer 21

Leads to allopatric speciation
Populations are physically separated
Barrier prevents gene flow between populations
Genetic changes occur in species (caused by genetic drift, mutations or natural selection due to different pressures in different areas)
Populations become so genetically different they can no longer interbreed to produce fertile offspring

Question 22

Reproductive isolation

Answer 22

Leads to sympatric speciation

Can be caused by: behavioural changes; biological changes; genetic changes

Question 23

Define artificial selection

Answer 23

Selective breeding of organisms in order to produce desired phenotypes in an organism (often beneficial to humans)

Question 24

Stages of artificial selection

Answer 24

Male and female with desired characteristic chosen
Male and female interbred
Best offspring selected and interbred
This is repeated over many generations

Question 25

Why is genetic material maintained in selective breeding?

Answer 25

Selective breeding tends to reduce the gene pool (so if there was a rapid environmental change the organisms would not have the variation to survive)

Question 26

What are gene banks?

Answer 26

Used to maintain a source of alleles for future breeding
Can counteract the loss in genetic variation, inbreeding and extinction
Can preserve currently unknown useful traits alleles (e.g. medicinal uses)
Can be seed/sperm/egg/embryo banks, rare breed farms, botanic gardens, zoos

Question 27

Points about inbreeding

Answer 27

As genetic diversity decreases with each generation, individuals become more related (inbred)
Likelihood of unintentionally selecting 2 copies of a harmful recessive allele can increase in a small gene pool
Can lead to increased susceptibility to disease
To avoid this, breeders can ‘outcross’ individuals with their wild types (or individuals from gene banks) to prevent the gene pool becoming too small

Question 28

Ethical considerations of selective breeding

Answer 28

Often doesn’t take into account animal welfare (inbreeding can increase susceptibility to disease)
Many domesticated animals would not survive if released into the wild (easy prey, wrong fat:muscle ratio to survive in cold)