Year 11 Biology (╥ ᴗ ╥)

NCEA level 1 revision

DNA

the molecule that stores and carries genetic information in living organisms.

Gene

A section of DNA that contains instructions for making a specific protein or functional product.

Allele

An alternative version of a gene.

Chromosome

A long, coiled DNA molecule containing many genes.

Locus

The specific position of a gene on a chromosome.

Genotype

The combination of alleles an organism has for a particular gene or characteristic.

Phenotype

The observable characteristic of an organism produced by its genotype and environmental influences.

Dominant allele

An allele that is expressed in the phenotype when at least one copy is present.

Recessive allele

An allele that is expressed in the phenotype only when no dominant allele is present.

Homozygous

Having two identical alleles for a particular gene.

Heterozygous

Having two different alleles for a particular gene.

Carrier

A heterozygous individual who carries a recessive allele but does not show the recessive phenotype.

Trait

A characteristic of an organism that can be influenced by genes and sometimes the environment.

Characteristic

An observable or measurable feature of an organism.

Protein

A molecule made of amino acids that performs specific functions in cells and can influence phenotype.

How are DNA, genes and proteins linked?

A gene is a section of DNA containing instructions for making a protein. The protein produced can influence an organism’s phenotype.

How can different alleles cause different phenotypes?

Different alleles can have different DNA base sequences, which may produce different proteins or amounts of protein, resulting in different phenotypes.

Nucleotide

The basic building block of DNA, made of a sugar, phosphate group and nitrogenous base.

DNA base

One of four chemical bases found in DNA: adenine, thymine, cytosine or guanine.

Adenine

A DNA base that pairs with thymine.

Thymine

A DNA base that pairs with adenine.

Cytosine

A DNA base that pairs with guanine.

Guanine

A DNA base that pairs with cytosine.

Complementary base pairing

The specific pairing of DNA bases where adenine pairs with thymine and cytosine pairs with guanine.

Base sequence

The order of nucleotide bases along a DNA molecule.

Genome

The complete set of genetic material in an organism.

Diploid

Having two sets of chromosomes, one set inherited from each parent.

Haploid

Having one set of chromosomes, as found in gametes.

Homologous chromosomes

A pair of chromosomes containing the same genes at the same loci, with one chromosome inherited from each parent.

Gamete

A reproductive sex cell containing half the normal chromosome number, such as a sperm or egg cell.

Fertilisation

The fusion of two gametes to form a zygote.

Zygote

A fertilised egg cell formed when male and female gametes fuse.

Mitosis

Cell division that produces two genetically identical daughter cells with the same chromosome number as the parent cell.

Meiosis

Cell division that produces genetically different haploid gametes with half the chromosome number of the parent cell.

Why is meiosis important?

Meiosis produces haploid gametes and creates genetic variation through processes such as crossing over and independent assortment.

Random fertilisation

The random combination of male and female gametes during fertilisation, increasing genetic variation in offspring.

Why does sexual reproduction create variation?

Meiosis produces genetically different gametes and random fertilisation combines them in different ways, creating genetically varied offspring.

Genetic variation

Differences in DNA, alleles or genotypes between individuals in a population.

Inherited variation

Genetic differences that can be passed from parents to offspring.

Environmental variation

Differences between individuals caused by environmental factors rather than inherited genetic differences.

Mutation

A change in the DNA sequence that can create a new allele.

How can mutation create variation?

A mutation changes DNA and can create a new allele, increasing genetic variation within a population.

Punnett square

A diagram used to predict possible allele combinations and the probability of different genotypes and phenotypes in offspring.

Monohybrid cross

A genetic cross that follows the inheritance of one gene or characteristic.

Probability

The likelihood that a particular genetic outcome will occur.

Pedigree

A diagram showing how a characteristic or allele is inherited through generations of a family.

Autosomal

Referring to a gene located on a non-sex chromosome.

Sex-linked

Referring to a gene located on a sex chromosome, usually the X chromosome.

How can you identify a recessive trait in a pedigree?

A recessive trait can appear in offspring even when neither parent shows the trait, if both parents carry the recessive allele.

How can you identify a dominant trait in a pedigree?

A dominant trait usually appears in every generation and affected individuals normally have at least one affected parent.

Population

A group of organisms of the same species living in the same area at the same time.

Gene pool

All of the alleles present within a population.

Allele frequency

The proportion of a particular allele within a population’s gene pool.

Natural selection

The process in which individuals with advantageous inherited characteristics are more likely to survive and reproduce, causing those alleles to become more common over generations.

Selection pressure

An environmental factor that affects which individuals are more likely to survive and reproduce.

Selective advantage

An inherited characteristic that increases an organism’s chance of surviving and reproducing.

Selective disadvantage

An inherited characteristic that reduces an organism’s chance of surviving or reproducing.

Adaptation

An inherited characteristic that increases an organism’s chance of survival or reproduction in a particular environment.

Evolution

A change in allele frequencies within a population over successive generations.

How does natural selection change allele frequency?

Individuals with advantageous alleles are more likely to survive and reproduce, so they pass those alleles to more offspring. Over generations, the advantageous alleles become more common.

DNA sequencing

Determining the exact order of nucleotide bases in a section of DNA.

How can DNA sequencing identify genetic differences?

DNA sequences from different individuals can be compared to identify differences in their base sequences.

Genome analysis

The examination and comparison of an organism’s complete genetic information.

Why do closely related individuals have similar DNA?

Closely related individuals have inherited more DNA from common ancestors, so their DNA sequences are generally more similar.

Variation within a population

Genetic differences among individuals belonging to the same population.

DNA → gene → protein → phenotype

DNA contains genes. Genes contain instructions for making proteins. Proteins influence cell structure or function, which can produce an observable phenotype.

Mutation → allele → variation

A mutation changes DNA and can create a new allele, adding genetic variation to a population.

Variation → selection → reproduction → allele frequency

Individuals vary genetically. Selection pressures favour some phenotypes. Those individuals reproduce more successfully, so their alleles become more common over generations.

Meiosis → variation

Crossing over and independent assortment during meiosis create genetically different gametes.

Fertilisation → variation

Random fertilisation combines genetically different gametes, creating unique allele combinations in offspring.

Why is genetic variation important for a population?

Genetic variation increases the chance that some individuals will have characteristics that help them survive environmental changes or selection pressures.

What is the difference between genotype and phenotype?

Genotype is the allele combination an organism has, while phenotype is the observable characteristic produced by the genotype and environment.

What is the difference between a gene and an allele?

A gene is a section of DNA controlling a characteristic, while an allele is an alternative version of that gene.

What is the difference between homozygous and heterozygous?

Homozygous means having two identical alleles, while heterozygous means having two different alleles.

What is the difference between mitosis and meiosis?

Mitosis produces two genetically identical diploid cells, while meiosis produces genetically different haploid gametes.

What is the difference between inherited and environmental variation?

Inherited variation is caused by genetic differences passed between generations, while environmental variation is caused by differences in surroundings or experiences.

Explain natural selection

the process where organisms with traits better suited to their environment tend to survive and reproduce more than others

Explain how a mutation can lead to evolution

A mutation may create a new allele. If the allele produces an advantageous phenotype, individuals carrying it may reproduce more successfully. The allele can then increase in frequency over generations, contributing to evolution.

Explain allele frequency

Allele frequency describes how common a particular allele is in a population. It can change over generations because of processes such as natural selection.

Genetic diversity

The variety of alleles and genetic differences present within a population or species.

Inbreeding

Nucleus

The organelle in a eukaryotic cell that contains the chromosomes and DNA.

Double helix

The twisted ladder shape of a DNA molecule.

Role of DNA in traits

DNA contains genes, and genes contain the instructions for making proteins that influence traits.

How do mutations form new alleles

A mutation changes the DNA sequence of a gene and can create a new version of that gene, called an allele.

Gamete

A reproductive sex cell, such as a sperm or egg cell, containing half the normal chromosome number.

Independent assortment

The random arrangement and separation of homologous chromosome pairs during meiosis, producing different combinations in gametes.

Inheritance

The passing of genetic information from parents to offspring.

Heterozygous

Having two different alleles for a particular gene.

Variation

Differences in characteristics between individuals of the same species.

Species

A group of organisms that can reproduce with one another and produce fertile offspring.

Population

A group of organisms of the same species living in the same area at the same time.

Why is genetic diversity important?

Greater genetic diversity increases the chance that some individuals have advantageous alleles that help them survive environmental change or disease.

How does inbreeding affect genetic diversity?

Inbreeding reduces genetic diversity because related individuals are more likely to carry the same alleles.

Environment

The surroundings and conditions in which an organism lives.

Novel allele

A new allele created by mutation.

How can mutation affect evolution?

Mutation can create a novel allele, and if it provides an advantage, natural selection may increase its frequency in the population.

gene tracking

The use of genetic information or genetic techniques to identify, compare, or follow traits and inheritance.

Trait screening

Testing or examining individuals to identify whether they have a particular genetic characteristic or allele.

Polymerase chain reaction (PCR)

A laboratory technique used to make many copies of a specific section of DNA.