Genetics

What is asexual reproduction?

Reproduction involving one parent that produces genetically identical offspring.

What is one advantage of asexual reproduction?

There is no need to find a mate.

What is another advantage of asexual reproduction?

It has a rapid reproductive cycle, allowing populations to increase quickly.

What is a disadvantage of asexual reproduction?

There is no genetic variation between offspring, so a population may be vulnerable to environmental changes or disease.

Why does asexual reproduction produce genetically identical offspring?

It involves mitotic cell division from a single parent without the fusion of gametes.

What is sexual reproduction?

Reproduction involving the fusion of male and female gametes from two parents.

What is one advantage of sexual reproduction?

It produces genetic variation in the offspring.

Why is genetic variation an advantage?

Some individuals may have characteristics that help them survive environmental changes or disease.

What is one disadvantage of sexual reproduction?

An organism must find a mate.

Why is sexual reproduction generally slower than asexual reproduction?

It requires the production and fusion of gametes and usually requires finding a mate.

What is meiosis?

A type of cell division that produces genetically different haploid gametes.

What does meiosis produce?

Four daughter cells, each containing half the number of chromosomes of the parent cell.

Why are cells produced by meiosis haploid?

They contain one set of chromosomes rather than two.

What is a gamete?

A reproductive cell containing a single set of chromosomes, such as a sperm or egg cell.

Why must gametes be haploid?

When two gametes fuse during fertilisation, their chromosomes combine to restore the diploid number.

How are the four cells produced by meiosis different from each other?

They are genetically different because meiosis produces variation.

What is DNA?

A polymer that contains genetic information and is made from nucleotides.

What shape is a DNA molecule?

A double helix consisting of two coiled strands.

What holds the two DNA strands together?

Complementary base pairs joined by weak hydrogen bonds.

What are the four bases found in DNA?

Adenine, thymine, cytosine and guanine.

What is complementary base pairing in DNA?

Adenine pairs with thymine, while cytosine pairs with guanine.

What is a nucleotide?

A unit of DNA consisting of a sugar, a phosphate group and one of four different bases.

What sugar is found in DNA nucleotides?

Deoxyribose.

What are the three components of a DNA nucleotide?

A sugar, a phosphate group and a base.

What is a polymer?

A large molecule made from many repeating smaller units called monomers.

What is the genome?

The entire DNA of an organism.

What is a gene?

A section of a DNA molecule that codes for a specific protein.

What is the relationship between a gene and DNA?

A gene is a section of a DNA molecule.

What is the purpose of genes?

They contain the instructions for making specific proteins.

How can DNA be extracted from fruit?

The fruit is mashed, detergent is added to break down cell and nuclear membranes, salt helps separate DNA from proteins, the mixture is filtered and cold ethanol is added to precipitate the DNA.

Why is detergent used when extracting DNA from fruit?

It breaks down the cell membranes and nuclear membranes, releasing the DNA.

Why is salt used when extracting DNA from fruit?

It helps separate DNA from proteins and other cellular material.

Why is cold ethanol used when extracting DNA?

DNA is insoluble in cold ethanol, so it precipitates and becomes visible.

Why is the fruit mashed during DNA extraction?

To break up the tissue and increase the surface area for the chemicals to act on the cells.

What determines the order of amino acids in a protein?

The order of bases in the DNA gene.

How does DNA determine the structure of a protein?

The base sequence determines the order of amino acids, which then fold into a specific three-dimensional shape.

Why is the shape of a protein important?

Its specific shape determines how the protein functions.

How does the base sequence of a gene affect an enzyme?

It determines the amino acid sequence, which determines the enzyme's specific shape and therefore its activity.

What are the two main stages of protein synthesis?

Transcription and translation.

What happens during transcription?

RNA polymerase produces a complementary mRNA strand from the DNA of a gene.

What is RNA polymerase?

An enzyme that binds to DNA and produces an mRNA strand during transcription.

Where does RNA polymerase bind?

To non-coding DNA located in front of a gene.

What is mRNA?

Messenger RNA, a single-stranded molecule that carries the genetic code from DNA to a ribosome.

What happens after mRNA is produced?

It attaches to a ribosome.

What is translation?

The process in which the ribosome uses the codons on mRNA to assemble amino acids into a polypeptide.

What is a codon?

A triplet of bases on mRNA that codes for a specific amino acid.

How many bases make up one codon?

Three bases.

What is tRNA?

A molecule that carries specific amino acids to the ribosome during protein synthesis.

How does tRNA help protein synthesis?

It carries amino acids to the ribosome in the correct order according to the mRNA codons.

What happens to amino acids at the ribosome?

They are linked together to form a polypeptide chain.

What is a polypeptide?

A chain of amino acids linked together.

What is the overall sequence of protein synthesis?

DNA is transcribed into mRNA, mRNA attaches to a ribosome, tRNA brings amino acids, and the amino acids are linked to form a polypeptide.

How can a genetic variant in non-coding DNA affect phenotype?

It can affect the binding of RNA polymerase and therefore alter the quantity of protein produced.

Why can changing the amount of protein produced affect phenotype?

The amount of a protein can affect how cells function and therefore affect an organism's characteristics.

How can a genetic variant in coding DNA affect phenotype?

It can alter the sequence of amino acids in a protein.

How can changing the amino acid sequence affect a protein?

It can change the protein's shape and therefore alter its activity.

What is phenotype?

The observable characteristics of an organism.

Who was Gregor Mendel?

A scientist whose experiments with pea plants helped establish the basic principles of inheritance.

What did Mendel discover?

He discovered patterns of inheritance and showed that characteristics are passed from parents to offspring through inherited factors, now understood as genes and alleles.

Why was inheritance difficult to understand before Mendel's work?

The mechanisms of inheritance and the existence of genes and chromosomes were not yet understood.

What organisms did Mendel study?

Pea plants.

What is an allele?

A different version of a gene.

Why are there differences in inherited characteristics?

Individuals can inherit different alleles of genes from their parents.

What is a chromosome?

A long, coiled DNA molecule containing many genes.

What is a gene?

A section of DNA that codes for a specific protein.

What is an allele?

A different version of a gene.

What is a dominant allele?

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

What is a recessive allele?

An allele that is only expressed in the phenotype when two copies are present, in a simple dominant-recessive inheritance pattern.

What is homozygous?

Having two identical alleles for a particular gene.

What is heterozygous?

Having two different alleles for a particular gene.

What is genotype?

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

What is phenotype?

The observable characteristic produced by an organism's genotype and environmental influences.

What is a gamete?

A haploid reproductive cell containing one allele for each gene.

What is a zygote?

The diploid cell formed when two gametes fuse during fertilisation.

What is monohybrid inheritance?

The inheritance of a characteristic controlled by a single gene.

What is a genetic diagram?

A diagram used to show how alleles can be inherited from parents to offspring.

What is a Punnett square?

A diagram used to predict the possible genotypes and phenotypes of offspring from a genetic cross.

What is a family pedigree?

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

What does a dominant allele mean in a genetic cross?

Only one copy is needed for the characteristic to be expressed.

What does a recessive allele mean in a genetic cross?

Two copies are normally required for the characteristic to be expressed.

What is the genotype of a homozygous dominant individual?

Two dominant alleles, such as AA.

What is the genotype of a heterozygous individual?

One dominant and one recessive allele, such as Aa.

What is the genotype of a homozygous recessive individual?

Two recessive alleles, such as aa.

What happens during fertilisation?

A male gamete fuses with a female gamete to form a diploid zygote.

How is the sex of human offspring determined?

By whether the sperm carries an X or Y chromosome.

What sex chromosomes does a human female usually have?

XX.

What sex chromosomes does a human male usually have?

XY.

What sex chromosome does an egg cell contain?

An X chromosome.

What sex chromosome can a sperm cell contain?

Either an X or a Y chromosome.

What happens if an X-carrying sperm fertilises an egg?

The resulting XX zygote will usually develop as female.

What happens if a Y-carrying sperm fertilises an egg?

The resulting XY zygote will usually develop as male.

What is the probability of an XX or XY outcome in a simple human sex-determination cross?

Approximately 50% XX and 50% XY.

What is probability?

A measure of how likely an event is to occur.

How is probability calculated?

Probability = number of favourable outcomes ÷ total number of possible outcomes.

What is the probability of an event expressed as a percentage?

Probability as a percentage = probability × 100.

What is a ratio?

A comparison of two or more quantities.

How can a genetic cross be analysed?

By calculating the possible genotypes, phenotypes, ratios and probabilities of offspring.

What is a monohybrid cross used for?

To predict the inheritance of a characteristic controlled by one gene.

What is codominance?

A situation where both alleles in a heterozygous individual are expressed in the phenotype.

What are multiple alleles?

When a gene has more than two possible alleles within a population.