Chapter 20 Inheritance

Question 1

What is your genotype? What is your phenotype?

Answer 1

Genotype- combination of alleles an organism inherits for a characteristic
Phenotype- observable characteristics of an organism

Question 2

What is a dominant allele? What is a recessive allele?

Answer 2

Dominant- always expressed in the phenotype if in the genotype
Recessive- only expressed in the phenotype if both copies of the allele are inherited

Question 3

What is discontinuous variation and what causes it?

Answer 3

Variation that falls into distinct categories, controlled by usually 1 gene, and not affected by the environment normally
E.g blood type, eye colour

Question 4

What is continuous variation and what causes it?

Answer 4

Variation that falls in a range with extreme values at each end, controlled by multiple genes and affected by the environment

E.g Height, weight

Shown as a bell curv

Question 5

What creates genetic variation?

Answer 5

Independent assortments of chromosomes during meiosis, metaphase, resulting in each gamete being genetically unique
Crossing over of non-sister chromatids during prophase and the formation of chiasmata, recombinant genes
Mutations
Chance- which of the gametes will fuse together

Question 6

What is chlorosis and etiolation?

Answer 6

Chlorosis- an inability to produce enough chlorophyll, due to environmental factors e.g insufficient minerals
Etiolation- lack of light causes causes extension of stem, but no increase in leaves, very tall thin plants

Question 7

What is monogenic inheritance and how do you perform a cross?

Answer 7

Looking at one gene, where one allele is dominant and another recessive

Punnet square, gametes in each side
G g
G GG Gg
G GG Gg

Question 8

What is co dominance? What is the result?

Answer 8

When two alleles of a gene are equally dominant so both are expressed in the phenotype
This normally means a mixed result
E.g red and white both dominant
Red and white protein made, so overall a pink colour seen

Question 9

How do you perform genetic crosses with codominance?

Answer 9

Put the characteristic first letter is caps
The allele is in subscript

e.g genotype= C^W C^R

Question 10

How is blood type inherited?

Answer 10

3 alleles- IA IB and Io
A and B codominant, result in AB blood type
Io recessive, only O is both alleles are O

Determines which type of antigen on blood cells

Question 11

What are sex-linked diseases? Why do disease proportions change depending on gender in these cases? Give an example

Answer 11

Alleles which are responsible are found on the sex chromosomes
If on the Y chromosome only, only affects males
If on the X chromosome but recessive, in males, only 1 recessive is needed as not on the Y,
No dominant to cancel it out, so disease more common
e.g Haemophilia

Question 12

What is a dihybrid cross?

Answer 12

A genetic cross used to show the inheritance of two different characteristics, could be on different pairs of homologous chromosomes so either linked or not linked

Question 13

Outline the genetic crosses for YyRr x YyRr (two heterozygous for both characteristics)?

Answer 13

Gametes- take all combinations

 YR  Yr  yR  yr  YR Yr yR yr

Put letters together when writing them out- first count how many have a capital of both
Then see how many left have 1 capital of each
Then how many with no capitals

Question 14

What are linked genes? How does it affect inheritance?

Answer 14

Genes which are found on the same chromosome so are inherited together unless there is crossing over

Likely not predicted, instead group your dominant alleles and your recessive alleles keep these gametes together
Any weird outputs are likely the products of crossing over

It is difficult to say which is which, but the phenotypic ratio from the predicted cross is wrong

Question 15

What is the autosome? What is autosomal linkage?

Answer 15

Autosome- non-sex chromosomes
Autosomal linkage- 2 linked genes found on the same autosomal chromosomes

Question 16

What is the formula for recombinant frequency? What does this mean in terms of linkage?

Answer 16

Recombinant frequency= (n of recombinant offspring (1 dominant and 1 recessive either way round) / (total alleles in offspring)

If greater than 50%, no linkage
The closed the genes are on the chromosomes, the lower the chance of crossing over

Question 17

What is the chi squared formula and how do you interpret the results? What is the degrees of freedom calculation?

Answer 17

Chi squared= the sum of (((o-e)^2)/e)
If Chi squared > d of freedom, we reject Ho, less than a 5% probability that these results are due to chance
D of freedom= n of categories - 1

There is not a SIGNIFICANT DIFFERENCE between the observed and expected ratio

Question 18

What is epistasis? Give an example

Answer 18

When the expression of one gene is effected by another, masked by the other

E.g if the first allele doesn’t protein A
But the second allele should make protein B from A as it has the genes
So it looks like A and B isn’t there, but B could be, but masked by A

Question 19

What is antagonistic epistasis? What is complementary epistasis?

Answer 19

Presence of a gene inhibits another
Presence of a gene encourages expression of another

Question 20

What is the hypostatic gene? What is the epistasis gene?

Answer 20

Hypostatic- the gene that is being controlled by another
Epistastic- the gene which is controlling the other

Question 21

What is recessive and dominant antagonistic epistasis?

Answer 21

Recessive- when two alleles needed to inhibit expression of another
Dominant- only one allele needed to inhibit the expression of another

Question 22

What is genetic diversity? What is allele frequency?

Answer 22

Genetic diversity- the genetic differences between individuals within a population
Allele frequency- how often an allele occurs within a population

Question 23

What is directional selection and give an example?

Answer 23

Individuals of certain characteristics favoured in one direction
E.g if climate becomes colder, longer hair furred individuals favoured, shifts to the right

Question 24

What is stabilising selection? Give an example

Answer 24

Average individuals favoured
E.g if the habitat conditions have been stable for a long time, no benefit to being in either extreme

Question 25

What are genetic bottlenecks?

Answer 25

Many alleles lost when a change in environment killed a large number of the population
New population descended from the few surviving members, so limited gene pool

Question 26

What is the founder effect?

Answer 26

A few migrate away and become isolated from the population
As only made of a few individuals, they have a reduced gene pool, with allele frequencies that differ to the main population
If mutations occur in one population but not the other, this increases the difference further
Some alleles are lost

Question 27

What is genetic drift? What is the gene pool?

Answer 27

Some characteristics are passed on by chance rather than due to factors that affect an individuals survival
Gene pool- all the alleles of all genes in all individuals in a population in a given time

Question 28

What the assumptions for the Hardy-Weinberg equation?

Answer 28

No selection
No migration
Random mating
No mutations
Large population

Question 29

How do you use the Hardy-Weinberg equation?

Answer 29

P is dominant Q is recessive
If looking at only appearance of the allele (homozygous or heterozygous ) use p + q= 1
If looking combination e.g only heterozygous, using p2 + 2pq + q2 = 1
Rearrange where necessary

Question 30

What is speciation? What are types of speciation?

Answer 30

Formation of a new species through the process of evolution
Allopatric- due members being separated by a physical barrier
Sympatric- within the same habitat so either behavioural or plants

Question 31

What is the process allopatric speciation?

Answer 31

Geographical isolation of some members of the species, resulting in reproductive isolation

Founder effect: the allele frequency of the founding members may not be representative of the original population e.g if a recessive allele present in these founders, could become more common.
Mutations occur in only one side of the population. If advantageous and able to help cope with selection pressures, the frequency of this allele increases, as the organism will be successful, reproduce, and pass on the allele
No gene flow between populations
Differing selection pressures mean successful characteristics in one population not the same as the other

Over time and many generations, the allele frequencies in each population are too different to enable breeding and the production of fertile offspring, and so two new species

Question 32

What is sympatric speciation and give an example?

Answer 32

Speciation within the same habitat
E.g plants
As long as even number of chromosomes are in the diploid cell, fertile offspring are formed, but may not be able to reproduce with the original species as differing chromosomes

Question 33

What is artificial selection?

Answer 33

Selective breeding

Same as natural selection but a leader choosing what characteristics are advantageous rather than for survival, changing allele frequency

Question 34

What are some ethical considerations for selective breeding?

Answer 34

Increased docility means they cannot return to the wild
Live stock more leans so easy ret and need to be housed as cold
Low gene pool increases risk of diseases especially inherited disease
Changing colours means a loss of camouflage

Question 35

What are gene banks?

Answer 35

Samples of DNA being stored
E.g as seeds, sperm, eggs
Used to increase genetic diversity

Question 36

What must occur for a new breed of species to form?

Answer 36

A mutation enabling new characteristics to develop
Selection pressure to make this characteristic desirable and defining

Question 37

How would genes being autosomally linked alter the predicted ratio of 9:3:3:1?

Answer 37

Closer to the parents ratio
e.g if both parents heterozygous, increased proportion of heterozygous individuals

Question 38

If performing a sex-linked allele genetic cross, how do you display the alleles?

Answer 38

X^br
Y

Even if codominant, importance of X/Y as the base

Question 39

Why will the observed ratio not exactly match the predicted ratio?

Answer 39

Random chance of which gametes fertilised so likely not exact

Question 40

How can you determine if a gene is sex-linked from a pattern of inheritance? What else can be determined?

Answer 40

If only one gender has it or its more frequent in one gender, likely sex-linked

Recessive if two parents can produce a child with it

If on the X chromosome, more likely in males if recessive as no other X dominant to cancel it out. If dominant, likely more female sufferers

If only in males, likely on the Y chromosome

Question 41

Why might a different ratio from 9:3:3:1 occur?

Answer 41

Epistasis, meaning not always expressed in the phenotype even if present
The genes are autosomally linked, meaning they are inherited together as on the same chromosome, so same as the parents
Any small numbers are the result of crossing over in meiosis
No independent assortment

Question 42

Why might of use of antibiotics be dangerous?

Answer 42

Presence of antibiotics acts as a selection pressure
Genetic variation within the bacteria, only some contain the allele for antibiotic resistance so survive, whilst the others die
Surviving bacteria advantageous, lowered competition, so successful and replicate, passing on alleles for antibiotic resistance to offspring
Allele frequency within the new population increases, if pathogenic, cannot be killed when used to combat disease

Question 43

Why is genetic drift more importance in small populations?

Answer 43

In small populations, one individual’s alleles have a greater proportional impact upon the whole population
So more likely that when this individual is lost, the allele is also lost

Question 44

How does stabilising selection affect a certain characteristic (6) ?

Answer 44

Pre existing variation from mutations, crossing over in meiosis and independent assortment, nature of sexual reproduction

Overproduction of offspring
Those at either extremes of the characteristic will die out as unable to survive e.g unable to eat fruit, without reproducing
Alleles of these organisms will be phased out

Average characteristic organisms more successful, able to survive and reproduce
Alleles for their characteristic size passed on, and over time and generations, this allele frequency increases

Use data to illustrate from graphs

Question 45

What conditions are needed for speciation to occur, not including a geographical barrier and reproductive isolation?

Answer 45

Mutations
Different selection pressures to other locations
Time

Question 46

Why is it important to keep a range of wild population of crops ?

Answer 46

Artificial selection- lowers gene pool of plants, so more susceptible to changes in the environment
Provide a source of genetic material, alleles for useful characteristics
Can be bred with crops to introduce characteristics
Unknown future demands, could be new disease, changing climate, so alleles not currently desirable may be required for the species to survive