Bio GCSE - inheritance

What is the Genome?

All the DNA (and genes) within an organism

What is a Gene?

A section of a DNA molecule that contains the code for a specific protein.

What is a chromosome?

A large, tightly coiled piece of DNA that contains genes - located in nucleous of cell.

Where are genes located in a cell?

Genes are located on chromosomes, which are found in the nucleus of a cell.

Describe the structure of a DNA molecule

Two strands coiled to form a double helix, linked by paired bases

What are the paired bases in DNA?

Adenine (A) pairs with Thymine (T). Cytosine (C) pairs with Guanine (G)

How does an RNA molecule differ from DNA?

RNA is single-stranded and contains the base Uracil (U) instead of Thymine (T)

What are the two stages of Protein Synthesis?

1. Transcription (DNA -> mRNA) and 2. Translation (mRNA -> Protein)

What is the role of mRNA?

Messenger RNA. It carries the genetic code from the DNA in the nucleus to the ribosome in the cytoplasm

What is the role of tRNA?

Transfer RNA. It carries a specific amino acid to the ribosome and matches its anticodon to an mRNA codon.

What is a codon?

A sequence of three bases on the mRNA that codes for one specific amino acid

What is transcription?

1. Section of DNA unwinds to expose nucleotides of the template strand (other strand is the coding strand).

2. Free floating RNA nucleotides line up against the template strand according to their complimentary base pairs (U goes with A).

3. Bonds form between adjacent RNA nucleotides to form a molecule of mRNA.

4. When the gene has been transcribes, the mRNA leave the nucleus through a nuclear pore.

5. The DNA strands r-join.

What is translation?

mRNA goes to ribosome where it is read in triplets by tRNA.

The tRNA has anticodons which are complimentary to the mRNA's codons.

The mRNA codes for amino acids which are held together by peptide bonds; they form a specific sequence of amino acids.

The chain stops when a stop codon is reached (codes for end amino acid) and it folds to become a protein.

What is a nucleotide?

a nitrogenous base, a phosphate group and a sugar molecule.

Nucleotides are bonded together through the bases which have hydrogen bonds (double for A - T and triple for C - G)

each DNA strand is made from these joined together

What is the product of mitosis?

Two daughter cells that are diploid and contain an identical set of chromosomes to the parent cell.

Purposes of mitosis

Growth, repair, cloning and sexual reproduction in some species.

What is the product of meiosis?

Four daughter cells that are haploid (half the number of chromosomes) and are genetically different.

produces gametes

Define Diploid and Haploid numbers in human cells.

Diploid (2n): 46 chromosomes. Haploid (n): 23 chromosomes

How does random fertilisation contribute to variation?

The random fusion of two gametes increases the genetic variation of the offspring.

What are the three sources of variation within a species?

Genetic (inherited), environmental (lifestyle/climate), or a combination of both.

Define an Allele.

An alternative form of a gene, giving rise to differences in characteristics.

Define Dominant and Recessive alleles.

Dominant: Always expressed. Recessive: Only expressed if two copies are present.

Define Homozygous and Heterozygous.

Homozygous: Two identical alleles (e.g., AA or aa). Heterozygous: Two different alleles (e.g., Aa).

Define Genotype and Phenotype.

Genotype: The genetic makeup (alleles). Phenotype: The physical expression (characteristic).

What does Codominance mean?

Both alleles for a gene are equally expressed in the phenotype (e.g., AB blood group).

What is Polygenic Inheritance?

When a phenotypic feature is controlled by many genes working together (e.g., height, skin colour).

What is monohybrid inheritance?

an individual inherits a characteristic which is determined by a single gene with 2 alleles

In humans, what determines the sex of the offspring?

The male parent's sperm, which carries either an X or a Y chromosome. (Female is XX, Male is XY).

What is a Mutation?

A rare, random change in the genetic material (DNA) of an organism that can be inherited.

How can a change in DNA affect the phenotype?

It can change the sequence of amino acids in a protein, altering its structure and function.

What is the typical effect of most genetic mutations?

No effect on the phenotype (some have a small effect; rarely a significant effect).

Name two types of mutagens that increase the rate of mutation.

Ionising radiation (X-rays, UV rays) and chemical mutagens (chemicals in tobacco).

Outline Darwin's Theory of Natural Selection.

Variation exists (due to random mutations).

Something is exerting selection pressure on the population(predator, competition etc).

Individuals with a characteristic better suited to the pressure is more likely to survive and reproduce.

They pass on their alleles and the characteristic becomes emphasised over generations.

Other individuals without the characteristic are decreased/ become extinct.

How does antibiotic resistance evolve?

A random mutation makes a bacterium resistant.

Non-resistant bacteria are killed by antibiotics.

The resistant bacteria survive and reproduce, increasing their number in the population.

What are test crosses?

used to determine the unknown genotype of an organism with a dominant phenotype by crossing it with an organism that has a known homozygous recessive genotype.

if all offspring show the dominant phenotype, the parent was likely homozygous dominant; if the offspring are split 50% dominant and 50% recessive, the parent was heterozygous.

What are family pedigrees?

diagrams that show the incidence of a particular trait across a dew generations of a family.

square = male and circle = female. shaded shapes show that the individual expresses the trait.

they help to determine the mode of inheritance (dominant or recessive) in a genetic condition