Genetic Variation And Change

Question 1

What is GENETIC VARIATION

Answer 1

Genetic variation is the genetic difference of alleles within the organism and within a population. It is the raw material for evolution as it is needed for natural selection

Question 2

What are the TWO SOURCES OF VARIATION

Answer 2

The two sources of variation are MEIOSIS and VARIATION.

Question 3

Explain the process of MEIOSIS and how it LEADS TO VARIATION

Answer 3

Meiosis is the process where 4 HAPLOID CELLS are produced with HALF THE NUMBER OF CHROMOSOMES from ONE DIPLOID CELL. There are THREE MAIN STAGES, crossing over, independent assortment, and segregation.

1. CROSSING OVER occurs during the METAPHASE of MEIOSIS. The CENTERAL CHROMATIDS of a HOMOLOGOUS PAIR of CHROMOSOMES SNAP and EXCHANGE pieces of DNA mixing information on the central chromatids.
   This process MIXES the EXISTING ALLELES into NEW COMBINATION, creating 4 GENETICALLY UNIQUE GAMETES at the END OF MEIOSIS.
2. INDEPENDENT ASSORTMENT occurs during the METAPHASE of MEIOSIS. The HOMOLOGOUS pair of CHROMOSOMES LINE UP at the EQUATOR of the CELL, INDEPENDENTLY of the other HOMOLOGOUS PAIRS. This process MIXES the existing alleles from the more and aether into new combinations due to the RANDOMNESS OF LINING UP.
3. SEGREGATION occurs durning the second stage of METAPHASE during MEIOSIS. This is when the chromosomes and the chromatids seperate randomly, creating new allele combinations so that each gamete gets just one copy of each chromosome

Question 4

Explain how MUTATIONS lead to GENETIC VARIATION

Answer 4

Mutations are a PERMANENT CHANGE in the DNA base sequence. When this occurs, it alters the function and expression of the gene, resulting in a new allele.

Question 5

Explain how BENEFICIAL MUTATIONS are RETAINED in a POPULATION

Answer 5

Beneficial mutations are retained in a population due to natural selection. If the mutation helps the organism to survive and reproduce within its environment then it is able to reproduce and pass it on to the offspring, causing the mutation to become more common in the population over a period of time.

Harmful mutations are not retained in a population because the organism with the mutation will not be able to to survive long enough to reproduce, thus not passing it on to the next generation.

Question 6

What is NATURAL SELECTION

Answer 6

Natural selection is whee nature will favour advantageous alleles over harmful ones to help the population to survive and reproduce.

Question 7

What is ALLELE FREQUENCY

Answer 7

Allele frequency is how common a specific allele is in a population compared to all the alleles for that gene.

Question 8

What is GENETIC DRIFT

Answer 8

Genetic drift is the CHANGE IN ALLELE FREQUENCY due to CHANCE. By ‘chance’ it means events as an organism dying who was the only one left with that certain allele in the population.

Question 9

What is MIGRATION

Answer 9

Migration is the movement of individuals from one population to another.

Question 10

Explain the FOUNDER EFFECT with a EXAMPLE

Answer 10

Founder effect is the differences in gene pools between an original population, and a new population related by its former members. This could look like a small group of individuals leaving a the larger population. Because the smaller group may or be able to carry all the alleles it has reduced genetic diversity making it susceptible to genetic drift.

Question 11

Explain the BOTTLENECK EFFECT with a EXAMPLE

Answer 11

The bottle neck effect is where a large population suddenly becomes smaller. This leaves a smaller population with reduced genetic diversity due to the change in allele frequency. Possibly alleles will be lost and the gene pool will have a different make-up because the new smaller population is just a sample size of the original population.

Question 12

What are LINKED GENES

Answer 12

Linked genes are genes that are closely located together on the same chromosome. Because they are physically close, they tend to inherited together during meiosis and less likely to be separated during crossing over.

Question 13

What are LETHAL ALLELES

Answer 13

Lethal alleles are alleles which cause death when they are in homozygous form, but allow heterozygous genotype to survive. (Sickle cell anaemia))

Question 14

What are MULTIPLE ALLELES

Answer 14

Multiple alleles are when a gene has two possible forms. (Blood or bunnies)

Question 15

What is COMPLETE DOMINANCE

Answer 15

Complete dominance is when the dominant allele completely mass over the recessive allele in a heterozygous individual. His is Mendelian genetics because it follows the clear traits of dominant and recessive patterns

Question 16

What is CO-DOMINANCE

Answer 16

Co-dominance is where two alleles are equally a fully expressed, so the physical expression of each allele can be seen in the individual. An example of this is Dalmatian dogs, they show co-dominance due to their black spots, because they are equally and fully expressed as the white colour, not having the dominant allele masking the other.

Question 17

What is INCOMPLETE DOMINANCE

Answer 17

Incomplete dominance is the inability for any allele to mask the other allele, resulting in a blended phenotype. An example of this is pink flowers, because they neither shoe the red phenotype or the white phenotype, but a rather blended/in between of pink.