Genetics, populations, evolution and ecoysystems

Question 1

Define a gene:

Answer 1

A sequence of baes of DNA molecules that codes for a protein (polypeptide) which results in a characteristic.

Question 2

Define an allele:

Answer 2

It is a different version of a gene and there can be different alleles of a single gene. They can be either dominant, recessive or codominant.

Question 3

Define a genotype:

Answer 3

The genotype is the genetic constitution of an organism.

Question 4

Define a phenotype:

Answer 4

The phenotype is the expression of this genetic constitution and its interaction with the environment.

Question 5

What is a dominant allele?

Answer 5

It is an allele who’s characteristics appears in the phenotype when theres only one copy. They have a capital letter.

Question 6

What is a recessive allele?

Answer 6

It is an allele whose characteristics only appears in the phenotype if two copies are present. They are shown by a lower case letter.

Question 7

What is a codominant allele?

Answer 7

They are alleles that are both expressed in the phenotype; neither ones recessive.

Question 8

What is a 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

What is a homozygote?

Answer 9

It is an organism that carries two copies of the same allele (BB/bb).

Question 10

What is a heterozygote?

Answer 10

An organism that carries two different alleles (Bb).

Question 11

Whats a carrier?

Answer 11

It is a person carrying an allele which isn’t expressed in the phenotype but can be passed onto an offspring.

Question 12

How are autosomal genes linked?

Answer 12

Autosomal genes aren’t sex chromosomes are located on autosomes. Genes on the same autosome are said to be linked because they stay together during independent segregation of chromosomes and their alleles will be passed on to the offspring; this won’t happen if crossing over splits them up first. The closer together two genes are on the autosome the more closely they’ll be linked as crossing over is less likely to split them.

Question 13

How does an epistatic gene mask the epression of another gene?

Answer 13

Many genes can control the same characteristics; they interact to form the phenotype. This can be because the allele of one gene mask (blocks) the expression of the allele of other genes; called epistasis.

Question 14

What is a specie?

Answer 14

It is defined as a group of similar organisms that can reproduce to give fertile offsprings and can exist as one or more populations.

Question 15

Define a population:

Answer 15

It is a group of organisms of the same species living in a particular area at a particular time so they have potential to interbreed.

Question 16

Whats the gene pool?

Answer 16

The gene pool is the complete range of alleles present in a population.

Question 17

What is the allele frequency?

Answer 17

How often an allele occurs in a population is called the allele frequency and is usually given as a percentage of the total population.

Question 18

What is the hardy-weinberg principle used for?

Answer 18

It provides a mathematical model which predicts the allele frequencies will not change from generation to generation . This prediction is only true under certain conditions; has to be a large population where theres no immigration, emigration, mutations or natural selection. There also needs to be random mating (all genotypes can breed with others).

Question 19

How does the equation precut allele frequency?

Answer 19

When a gene has two alleles you can figure out one of the allele of the gene if you know the frequency of the other allele using this;
p + q = 1
p= frequency of one allele (usually dominant).
q= frequency of other allele (usually recessive).

Question 20

How does the equation predict genotype and phenotype frequencies?

Answer 20

p^2 + 2pq + q^2 = 1
p^2= frequency of the homozygous dominant genotype.
2pq= frequency of the heterozygous genotype.
q^2= frequency of the homozygous recessive genotype.

Question 21

How does the equation predict the percentage of a population that has a certain genotype?

Answer 21

p + q = 1

p^2 + 2pq + q^2 = 1

Question 22

What is variation?

Answer 22

Variation is the differences that exist between individuals. Variation within a specie means individuals in a population can show a wide range of phenotypes. They have the same genes but different alleles which causes genetic variation within a species. The main source of this genetic variation is mutations. Crossing over and independent segregation also introduced genetic variation. Variation within species is caused by differences in the environment and by a combination of genetic and environmental factors; results in evolution.

Question 23

What is evolution?

Answer 23

The frequency of an allele in a population changes over time; this is evolution. Natural selections one method by which evolution occurs.

Question 24

What is natural selection?

Answer 24

Individuals of the same species vary because they have different alleles. Predation, disease and competition (selective pressures) create struggle for survival as individuals vary (some better adapted for pressures than others). This means theres differential levels of survival and reproductive success in a population and individuals with a phenotype that increases their chance of survival are more likely to survive, reproduce and pass on their genes. This means that a greater proportion of the next generation inherit beneficial alleles and are more likely to survive, reproduce and pass on they genes. The frequency of the beneficial alleles in the gene pool increase from generation to generation.

Question 25

What is stabilizing selection?

Answer 25

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

Question 26

What is directional selection?

Answer 26

It is where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce and this could be in response to an environmental change.

Question 27

What is disruptive selection?

Answer 27

It is where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce. It is the opposite of stabilizing selection because characteristics towards the middle of the range are lost. It occurs when the environment favors more than one phenotype.

Question 28

What is speciation and when does it occur?

Answer 28

Speciation is the development of new species from existing species and it occurs when populations of the same species become reproductively isolated; changes in allele frequency causes change in the phenotype which means they no longer interbreed to produce fertile offspring. This can happen when a physical barrier (earthquake) divides a population of species causing some individuals to become separated from the main population; known as geographical isolation and leads to allopatric speciation.
Speciation can also occur when a population becomes reproductively isolated without any physical separation; known as sympatric speciation.

Question 29

How does allopatric speciation require geographical isolation?

Answer 29

Geographically separated populations experience different conditions. This means populations will experience different selection pressures and so different changes in allele frequencies occur: different alleles will be more advantageous in different populations. Te change in allele frequencies leads to differences in accumulating in the gene pools of the separated populations causing changes in phenotype frequencies. Individuals from different populations won’t be able to breed with one another to produce fertile offspring (they’ll become reproductively isolated).