NCEA L2 Genetics Flashcards

A twisted ladder like structure composed of two strands of DNA. The sides of the double helix is composed of the sugar phosphate backbone. The phosphate of one nucleotide is bonded to the sugar of another nucleotide. The hydrogen bonds between the phosphates cause the DNA strand to twist. The nitrogenous bases point inward on the ladder and form pairs with bases on the other side like rungs.Each base pair is formed from two complementary nucleotides (purine with pyrimidine) bound together by hydrogen bonds.

A nucleotide is a molecule that is the building block of DNA and RNA. It is made up of three parts: a phosphate group, a five-carbon sugar, and a nitrogenous base.

The bonds that hold the base pairs together in the DNA sequence

Sugars (deoxyribose) and phosphate groups are bonded by phosphodiester bonds, forming the ‘sides’ of the DNA ladder; giving the DNA its structure and formity. A sugar-phosphate backbone joins together nucleotides in a DNA sequence.

A single ringed structure. The pyrimidine bases are Cytosine and Thymine.

A double ringed structure. The purine bases are Adenine and Guanine.

These are the four nitrogenous bases that make up DNA. They are found in pairs

A-T,

C-G.

These base pairs are read in groups of 3, when the DNA is read to code for traits. If one of these bases are doubled, removed or incorrectly bonded like sometimes happens during mutation it alters the way the DNA is read.

DNA is a polymer (single chain) made of nucleotides. Each nucleotide is made of a sugar (deoxyribose) connected to a phosphate group and bound to on the other side to a nitrogenous base (A, T, C, G). Our DNA guides the cell in making new proteins that determine all of our biological traits and gets passed (copied) from one generation to the next.

Adenine (A) and Thymine (T) are complementary, meaning they always pair together and Cytosine (C) and Guanine (G) are complementary.

A variation of a gene. These code for specific traits such as the colour of your eye and the colour of your hair.

A strand/section of DNA that holds the instructions for one protein. This protein then codes for a specific trait.

Tightly wound DNA that contains the genetic information for an organism's characteristics.

Chromatids are what chromosomes are called during cell division, when they are linked by the centromere. They are identical halves of a chromosome, called sister chromatids.

Two members in each pair of chromosomes with similar size & shape, centromere in the same place, identical genes at same locus but may be different alleles

Maternal means that it is passed down from the mother and paternal means that it is passed down from the father.

Genetic variation is naturally occurring genetic differences among individuals of the same species. This variation can increase the chance of survival of a species should their environment change. Genetic variation can be caused by lots of different factors such as migration, genetic drift, Natural selection, mutation, sexual reproduction (meiosis).

Non-heritable variations are those caused by the environment. (mutations)

Heritable variations are those which are inherited from parents (sexual reproduction-meiosis)

All the many characteristics which make up an individual, including its appearance, are called its phenotype. Each phenotype is a blend of heritable and non-heritable characteristics. Mutation as the ultimate source of genetic variation within the gene pool.

Mutations usually have negative impacts on a phenotype, but occasionally they can act positively, for instance, by improving the individual's fitness in its environment. This means they will be “selected for” and so increase in frequency in a population.

A randomly occurring permanent change to the base sequence in the DNA in a gene or chromosome that may create new alleles. Mutations are the only way new alleles are formed and so are known as “the ultimate source of variation”. Without mutation there would be no variation, and without variation there would be no evolution.

The passing on of particular traits from an individual to its offspring

Something that speeds up the process of a mutation. mutagens can include chemicals, UV rays (i.e. sunlight) and radiation (i.e. x-rays and radioactive materials). Affect the nucleotides themselves: converting one base to another, knocking a base off its backbone, or even causing a break in the DNA strand.

Gametic is the sex cells eg egg, sperm. They contain half the normal amount of genetic material (23 chromosomes) the genetic material contained within the gametic cells can be passed on to another generation through reproduction. Any mutations that occur in these cells can be passed on.

Somatic is the cells in the body containing 46 chromosomes. Somatic mutations are not passed on from one generation to the next. Somatic mutations only affect the individual organism in which the cells have mutated because body cells are not inherited

Evolution is the slow development/change in a species genetic material. Evolution is often to help a species survive in a certain environment or adapt to a new predator or threat. It takes place over many generations and the change in traits are carried on through reproduction.

Genetically varied species have different traits which may be better suited to a change in the environment. The individuals with the favourable traits will go on to reproduce, meaning that their offspring will inherit the favourable trait. Those with unfavourable traits will die due to the change in environment and therefore will not be able to reproduce. Therefore, the trait is removed from the genepool, increasing the chances of survival of the species. Driving force of evolution.

A breeding experiment where we are considering only one characteristic.

Insertions and deletions can alter a gene so that its message is no longer correctly read.

Mutation that exchanges one base for another (i.e., a change in a single "chemical letter" such as switching an A to a G).

Mutations in which extra base pairs are inserted into a new place in the DNA.

An exchange of genetic material between adjacent chromatids of homologous chromosomes during meiosis. results in novel combinations of alleles on the chromosomes, creating almost infinite potential for variation.

When each of the 23 chromosome pairs line up during the first phase of meiosis completely randomly before the cell splits, leading to genetically different daughter cells.

During meiosis, pairs of alleles are segregated when the homologous chromosomes split so that each gamete only receives one allele for each pair. Segregation results in all daughter cells being unique.

Mutations in which a section of DNA is lost, or deleted.

Crossing Over
Independant Assortment
Random Segregation
Gamete Fusion

In humans, diploid cells contain 46 chromosomes whilst haploid cells only contain half of this number (23 chromosomes). Generally, all cells in the human body (except red blood cells and gametic cells) are diploid cells. Whilst the sperm in men and eggs in women contain 23 chromosomes.

The proteins which DNA is tightly bound to in chromostins.

The centromere links a pair of sister chromatids together during cell division.

Refers to the location on the chromosome where the gene is found. SInce most organisms have two sets of chromosomes, they have (except on the sex chromosomes) two alleles at each gene locus.

One of the numbered chromosomes, as opposed to the sex chromosomes. Humans have 22 pairs of autosomes and one pair of sex chromosomes (XX or XY). Autosomes are numbered roughly in relation to their sizes.

A type of chromosome involved in sex determination. Humans and most other mammals have two sex chromosomes, X and Y, that in combination determine the sex of an individual.

How common an allele is in a population

A structure that forms between a pair of homologous chromosomes by crossover recombination and physically links the homologous chromosomes during meiosis.

The dominant allele completely masks the effect of the recessive allele in the heterozygous condition.

When the two alleles combine to create an intermediate or blended phenotype

When both alleles are expressed separately. Human blood type is a good example of this.

A description of the appearance of an organism. Any characteristic can have several phenotypes, e.g. a daffodil can have a yellow flower colour or orange flower colour or white flower colour.

An individual with a homozygous genotype.

Tells us which allesles are present.

• Fertilisation is a random process
• Sample was not big enough

Genes have more than two allelic forms.

Alleles that cause the death of the organism that carries them. They are usually a result of mutations in genes that are essential for growth or development. Recessive lethal alleles only kill homozygotes. Lethal alleles are often detected as the ratio of expected progeny is distorted

Performed in order to decide the genotype of a dominant appearing parent. Breed an individual with a known genotype with a individual with a dominant phenotype to see if the individual is hetrozygous or homozygous dominant.

Dihybrid cross is a cross between two individuals with two observed traits that are controlled by two distinct genes

Two genes that occur on the same chromosome are said to be linked, and those that occur very close together are tightly linked. the observed ratio will be quite different from that seen for unlinked traits. Allele combinations that began together will tend to stay together, and the offspring will show a skewed ratio reflecting the original combinations. If the loci for the two genes are very close, crossing over is unlikely to separate alleles, whereas if they are far apart, crossing over is much more likely to separate them. They do not assort independently, whereas genes located on different chromosomes assort independently and have a recombination frequency of 50%, linked genes have a recombination frequency that is less than 50%.

The change in frequency of alleles in the gene pool of a population

Total number of alleles that exist for a population

A group of individuals of the same species in the same place at the same time.

Change in the allele frequencies of populations due to a chance event. Alleles can be lost from the gene pool. Like migration, genetic drift is most likely to affect smaller populations. This is not a form of natural selection as they don't disappear from the gene pool due to lack of fitness but rather due to chance

Occurs when a small group of individuals colonizes a new isolated area. They form the founder population. The range and frequency of alleles in the founder population is unlikely to be representative to that of the original population. Some alleles might not be present at all in the founder population whereas others might be more or less frequent.

Occurs when a population may be suddenly reduced in numbers to a small size. The population numbers then increase but diversity has been lost s the survivors are all descended from the small group that came through the bottleneck. This can be the result of: a catastrophic environmental event or a human action. As individuals are removed their alleles are removed from the gene pool. This results in changes in allele frequencies. The population will have reduced biodiversity.

The movement of individuals from one population to another (can reduce genetic diversity)

Individuals coming in (can increase genetic biodiversity if a new allele comes in)

Individuals leaving

Maintains the population in a stable form by favouting the average and selecting against the extremes in either direction.

Favors the phenotype of one extreme, so that there is a shift if the average, so there is a shift of the average in one extreme, therefore a shift in one direction.

Favors both extremes at the expense of the average.