Genetic Variation - questions

Question 1

Explain why linked genes produce less gametic variation by relating to independent assortment
M/E

Answer 1

Independent assortment is when homologous pairs of chromosomes line up at the equator during meiosis. They randomly assort themselves on either side, creating new combinations of alleles. If the genes are linked they CAN not seperate during meiosis, and therefore create less possible combinations of alleles, decreasing genetic variation.

Question 2

Define linked genes
A

Answer 2

Linked genes are alleles on the same chromosome that usually stay together during meiosis. They can be separated due to crossing over, which occurs before independent assortment

Question 3

Define crossing over
A

Answer 3

Crossing over is the exchange of alleles between
homologous pairs of chromosomes. It occurs during meiosis.

Question 4

Explain how crossing over creates more genetic variation in gametes related to the linked genes
M/E

Answer 4

Linked genes can be separated by crossing over (the exchange of alleles between homologous chromosomes), and this produces chromosomes that have different and / or new combinations of alleles. This increases genetic variation as these genes would normally be inherited together, but are separated to become unlinked gene/traits. e.g. red hair and freckles are typically inherited together but can be separated, meaning offspring could have freckles but no red hair or vice versa.

Question 5

Define Multiple Alleles

Answer 5

Multiple alleles are the many different versions of a trait that exist within a population. This results in more than 2 different phenotypes.

Question 6

Explain that an allele that is recessive is hidden by the presence of a dominant allele and can result in a parent producing offspring that have a different phenotype to them

M/E

Answer 6

In complete dominance, if a dominant allele is present it will always be expressed, and will be the phenotype. Recessive alleles are only expressed in the phenotype when both alleles inherited are recessive and there is no dominant alleles. Offspring can have different phenotypes to their parents. A reason for this if a parent with the resessive allele for eye colour has offpsring with a parent who has the homozygous dominant allele for eye colour, there is no way for offspring to receive the dominant phenotype (they may still get a recessive allele if they are heterozygous). - draw a punnet square

Question 7

Define natural selection
A

Explain how some alleles become more common by natural selection (relate to context)
M/E

Answer 7

The process in which organisms with traits better suited to their environment tend to survive longer and therefore produce more offspring and pass on their alleles.

Natural selection is based on traits (phenotypes) and influenced by selection pressures. If more offspring are produced than can survive, this leads to competition for resources. Some will have traits (adaptations) that are better suited to the environment. These organisms will be able to survive longer and have a greater chance of reproducing. These alleles will also become more common in the gene pool leading to less variety.

Question 8

Define selection pressures

Answer 8

Selective pressures are variables which cause a certain phenotype of an organism to have a better chance of surviving and reproducing. Selective pressures drive evolution via natural selection

Question 9

Explain how mutations add to variation in a population (relate to context)

Answer 9

If a genetic mutation occurs in one person, That person may pass their genetic mutation onto their children, and it could continue for generations. There would be extra genes/alleles in the population. If the mutation improves that person’s chance of survival, or freedom from disease, then it begins being passed through generations and spread through the population. As the mutation passes from generation to generation, it becomes a normal part of the human genome and evolves from a gene variant into a normal gene.

Question 10

Explain how selection pressures are involved in natural selection
M/E

Answer 10

If an organism has a more beneficial trait, If there exists an environmental influence that causes selective pressure and the favouring of one particular phenotype, it is likely that that the favoured phenotype would be more abundant in the population or more favourable to mate with. This causes the phasing out of the other phenotypes.

Question 11

Explain Why variation is important
M/E

Answer 11

Without variation, species can not evolve. Variations in a species of an organism helps to adapt in the environment, it also prevents the extinction of a species

Question 12

Define Genetic Drift
A

Answer 12

Genetic drift is the random change in allele frequency due to chance

Question 13

Explains how genetic drift occurs - relate to small populations
M/E

Answer 13

Can be due to natural disaster or just by chance didn’t get to reproduce. e.g. If an insect gets squashed by your foot, it is not due to bad phenotype but does still remove traits/alleles. Genetic drift has a big effect on small populations. If only a few individuals in the population have these specific alleles and some die then their alleles are gone from the population. This means there is less variety to pass on.

Question 14

Define allele frequency
A

Answer 14

Allele frequency is the frequency of an allele divided by the total number of different alleles in the gene pool.

Question 15

Define gene pool
A

Answer 15

A gene pool refers to the the number of all the genes present in a reproducing population or species.

Question 16

Define bottleneck effect
A

Answer 16

The bottleneck effect is a sharp reduction in the size of a population due an environmental factor

Question 17

Explain how a bottleneck effect occurs and influences allele frequency
M/E

Answer 17

Bottleneck occurs becuase of an environmental factor e.g. flood wipes out majority of a population. With part of the population gone the amount of the species left is smaller, and therefore is less allele frequency and variation when it comes to reproducing

Question 18

Describe genetic diversity
A

Answer 18

Genetic Diversity refers to the range of different inherited traits within a species

Question 19

Define independent assortment

Answer 19

Independent assortment is when homologous pairs of chromosomes line up at the equator during meiosis. They randomly assort themselves on either side, creating new combinations of alleles.

Question 20

Define meiosis

Answer 20

Cell division that results in four non-identical gametes each with half the chromosome number of the parent cell (haploid)

Question 21

Define segregation

Answer 21

During meiosis, the pair of alleles segregate (separate) and are passed into different gametes

Question 22

Define fertilisation

Answer 22

Fusing of egg and sperm to make an offspring

Question 22

Define lethal alleles

Answer 22

A lethal allele is an allele which when present will lead to the premature death of the organism

Question 23

Define codominance

Answer 23

When both alleles in a heterozygous genotype are dominant and are equally and independently expressed – e.g. the human blood type AB

Question 24

Define incomplete dominance

Answer 24

Incomplete dominance refers to the inability for any allele to mask another allele. This Results in a blended phenotype.

Question 25

Define mutations

Answer 25

A change in the base sequence of DNA. Can occur randomly or as a result of a mutagen

Question 26

Define migration

Answer 26

Migration is new individuals coming in which may introduce new alleles to a population - increasing variation, or individuals leaving a population which may lead to alleles being lost

Question 27

Define population

Answer 27

All the members of one species that live in a defined area

Question 28

Define founder effect

Answer 28

Random changes to a gene pool due to a few individuals establishing a new population. E.g. blown or drift to a separate island.