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Flashcards in Variation Definitions Deck (50):
1

Founder Effect

A small group of individuals that colonises a new isolated area, such as an island.

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Heterozygous

Having two different alleles for a trait eg. Hh

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Natural Selection

The environment selecting for/against certain phenotypes

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Heredity

The passing on of characteristics from an individual to its offspring

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Homologous chromosomes

identical pairs of chromosomes

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Incomplete Dominance

When both alleles are present, they are blended in the phenotype.
Eg. RR = red rr = white Rr = pink (snap dragons -flowers)

7

Multiple Alleles

Occur with genes that have more than two different alleles though an individual will only have two of them in its genotype.
eg. blood groups ABo -both A and B are co-dominant, dominant over o

8

Complete dominance

A dominant allele completely masks the presence of the recessive allele.
The recessive allele is only expressed in the phenotype when only recessive alleles are present.

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Independent assortment

Occurs during meiosis, when the homologous pairs line up in a random order during metaphase.

10

Artificial Selection

Selective breeding -People, not the environment, select the individuals that will breed and therefore determine what traits/alleles are passed on to offspring.

eg. dog breeds

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Variation

Slight differences between individuals within a population (or between populations)

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Law of segregation

Independent separation of alleles on separate chromosomes.

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Gene pool

Total amount of genetic material (alleles) of a population

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Recessive

An allele that is masked when a dominant allele is present

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Genetic drift

random changes in the allele frequency in small populations often due to chance events such as migration or natural disasters.
Survivors are LUCKY, not FIT
Deceased are UNLUCKY, not UNFIT

16

Sex-linked traits

Characteristics that are inherited from genes found in the sex chromosomes
(most are found on the X Chromosome)

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Somatic cell

Body cell

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Linked genes

Two genes on the same chromosome during meiosis.
If they are close together they will likely stay linked.
If they are far apart they will likely
Two genes very close together on a single chromosome typically travel together (rather than independently)

19

Gene flow

(migration) any movement of individuals, and/or the genetic material that they carry, from one population to another

20

Founder Effect

A small group of individuals that colonises a new isolated area, such as an island.
Allele frequency may change, this is due to CHANCE

21

Meiosis

A type of cell division that produces 4 unique daughter cells each containing half of the original number of chromosomes.

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Cell cycle

series of events that take place in a cell leading up to its division and replication.

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Mutations

Permanent change in the base sequence of DNA

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Selection Pressures

Something that forces a population to evolve (an actual 'pressure' that makes the population change genetically)

Competition, predators, lack of sufficient resources, drought, high energy cost, or redundant physical feature

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Directional Selection

Selection in favour of the extreme

eg. Darwin's Finch

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Allele

Alternative form of a gene

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Gene

The set of information that controls a trait; code in the DNA

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Locus

certain location or place

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Bottleneck Effect

Disasters can reduce a population to few survivors. Deaths are offten random, so survivors are not representative of the original gene pool.
The allele frequency may change, this is due to individuals surviving due to CHANCE

30

Lethal alleles

When a mutation results in an allele that produces a non-functional version of an essential protein.
If an individual inherits a lethal combination of mutated alleles it will die before or shortly after birth.

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Variation

Slight differences between individuals within a population (or between populations)

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Genotype

Genetic makeup of an individual for a characteristic

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Beneficial (advantageous) mutations

Increase an individual's fitness, therefore will increase in the gene pool

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Deleterious (harmful) mutations

Decrease an individuals fitness, therefore will decrease in frequency in the gene pool.

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Mutations

Permanent change in the base sequence of DNA

36

Sexual Selection

Individuals compete to choose mates with desirable characteristics -inheritable characteristics of the 'winner' -then passed on
usually female choosing male

eg. peacock -females dull in colour, male large tail v colourful
female selects most attractive male

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Gene

Is a specific length of DNA on a chromosome that has information that determines a particular protein, which determines a characteristic.

38

Genetic Biodiversity

The abundance of alleles within a population.
Greater biodiversity = greater abundance of alleles present

39

Disruptive Selection

Both extremes are favoured resulting in 2 distinct new species

eg. peppered moths
-white in rural areas to blend w/ white trees
-black in industrial areas to blend w/ black soot-covered trees

40

Co-dominance

When both alleles are present, they are both expressed in the phenotype
(Co-dominant alleles are both capitals to show they are both dominant)
eg. RR = red coat cow WW = white coat cow RW = red and white coat cow

41

Locus

certain location or place

42

Crossing Over

Occurs during Prophase 1 of meiosis, when parts of the chromosome of non-sister chromatids can cross over at a point called a chiasma, followed by breaking and recombining.
Result: Linked alleles are separated, so different combinations of alleles from those of the parents can result.

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Phenotype

The physical expression of a gene. Can be altered by the environment.

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Gametic cell

sex cells

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Gametic cell

sex cells

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Stabilising Selection

Selection in favour of the average

eg. baby birth weights

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Polygenetic Inheritance

When a single trait is influenced by many genes

48

Dihybrid inheritance

Is the inheritance of two genes controlling two different features.
The genes may have two or more different alleles.

49

Dominant

An allele whose trait -when present- always shows up in the organism's phenotype

50

Homozygous

Having two identical alleles for a trait eg. HH or hh