Inheritance

Question 0

Define phenotype

Answer 0

The observable characteristics of an organism, it is the result of the interaction between the expression of the genotype and the environment. The environment can alter an organisms appearance

Question 1

Define genotype

Answer 1

Genetic constitution (make up) of an organism. Describes all the alleles that an organism contains

Question 2

A gene is….

Answer 2

A section of DNA, is a sequence of nucleotide bases that usually determine a single characteristic of an organism, it does this by coding for particular polypeptides (proteins). Genes exist in 2 or more different forms called alleles. The position of a gene on a chromosome is known as the locus

Question 3

An allele is…

Answer 3

One of the different forms of a gene. Have 2 alleles of each gene, one from each parent. The order of bases in each allele is slightly different, they code for different versions of the same characteristic

Question 4

Define co-dominant

Answer 4

2 alleles both contribute to the phenotype, neither one is recessive

Question 5

Define multiple alleles

Answer 5

When a gene has more than 2 allelic forms

Question 6

Define dominant

Answer 6

An allele whose characteristic always appears in the phenotype even when there’s only one copy. Dominant alleles are shown by a capital letter

Question 7

Define recessive

Answer 7

An allele whose characteristic only appears in the phenotype if 2 copies are present. Recessive alleles are shown by a lower case letter

Question 8

Define locus

Answer 8

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

Question 9

Define homozygote

Answer 9

An organism that carries 2 copies of the same allele

Question 10

Define heterozygote

Answer 10

An organism that carries 2 different alleles

Question 11

What is monohybrid inheritance

Answer 11

The inheritance of a single characteristic (gene) controlled by different alleles

Question 12

Monohybrid crosses show….

Answer 12

The likelihood of alleles (and so different versions of the characteristics) being inherited by offspring of particular parents

Question 13

What is a punnet square

Answer 13

Another way of showing a genetic diagram, they’re also used to predict the genotypes and phenotypes of offspring

Question 14

A carrier is….

Answer 14

A person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring

Question 15

Genetic pedigree diagrams show…

Answer 15

How traits run in families

Question 16

Cystic fibrosis info

Answer 16

An inherited disorder that’s caused by fault recessive allele, codes for a faulty chloride ion channel. A person will only have the disorder if they’re homozygous for the allele, they must inherit 1 recessive allele from each parent. If a person is heterozygous they won’t have cystic fibrosis but they’ll be a carrier

Question 17

What is a species

Answer 17

A group of similar organisms that can reproduce to give fertile offspring

Question 18

What is a gene pool

Answer 18

The complete range of alleles present in a population

Question 19

What is the allele frequency

Answer 19

How often an allele occurs in a population

Question 20

What does the hardy-weinburg principle predict

Answer 20

That the frequencies of alleles in a population won’t change from one generation to the next.

But this prediction is only true under certain conditions-has to be large population where there’s no migration, no mutations, no natural selection but there is random mating

Question 21

The frequency of an allele within a population changes. This can happen when…

Answer 21

The allele codes for a characteristic that affects the chances of an organism surviving

Question 22

What is differential reproductive success

Answer 22

Individuals that have an allele that increases their chance of survival are more likely to survive, reproduce and pass on their genes, than individuals with different alleles. This means that a greater proportion of the next generation inherit the beneficial allele. They in turn are more likely to survive, reproduce and pass on their alleles. So the frequency of the beneficial allele increases from generation to generation. Process is called natural selection

Question 23

2 types of natural selection

Answer 23

Stabilising selection

Directional selection

Question 24

What is stabilising selection

Answer 24

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. It occurs when the environment isn’t changing, and it reduces the range of possible phenotypes

Question 25

What is directional selection

Answer 25

Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. This could be in response to an environmental change

Question 26

What is speciation

Answer 26

The development of a new species

Question 27

Speciation occurs when…

Answer 27

Populations of the same species become reproductively isolated. This can happen when a physical barrier, eg a flood or an earthquake, divides a population of a species, causing some individuals to become separated from the main population. This is known as geographical isolation. Populations that are geographically separated will experience slightly different conditions eg different climate on each side of physical barrier. The populations will experience different selective pressures and so different changes in allele frequencies

Question 28

Populations will experience different selective pressures and so different changes in allele frequencies. Explain

Answer 28

Different alleles will be more advantageous in the different populations. Eg if geographical separation places one population in colder climate than before, longer fur length will be beneficial. Directional separation will then act on the alleles for fur length in this population, changing the frequency of the allele for longer fur length. Allele frequencies will also change as mutations will occur independently in each population

Question 29

In speciation, the changes in allele frequency will lead to….

Answer 29

Differences accumulating in the gene pools of the separated populations, causing changes in phenotype frequencies. Eventually, individuals from different populations will have changed so much that they won’t be able to breed to produce fertile offspring, have become reproductively isolated. 2 groups become separate species