Genetic Diversity

What is a gene mutation?

A change in the DNA base sequence

What 3 things can increase the rate of mutations?

UV light, chemicals or viruses

What are the three types of gene mutations?

1. Substitution- one base is replaced by another

2. Deletion- one base is removed from the sequence

3. Insertion- one base is added into the sequence

Why are deletion and insertion mutations more likely to change amino acid sequence?

Because they cause frameshift

What are the two main types of mutations in chromosomes?

1. Polyploidy- when the organisms have more than two sets of chromosomes

2. Non disjunction- when homologous chromosomes fail to seperate in meiosis resulting in gametes with extra or missing chromosomes and leads to individuals with extra or missing chromosomes in all cells

What happens in prophase 1 in meiosis?

Chromosomes condense and homologous chromosomes pair up, centrioles migrate to opposite poles of the cell where each centriole starts forming spindle fibres, nucleolus disappears and the nuclear envelope starts to break down leaving the chromosomes free in the cytoplasm

What happens in metaphase 1 in meiosis?

Chromosomes line up along the equator of the cell in their homologous pairs, each chromosome attaches to the spindle by their centromere

What happens in anaphase 1 in meiosis?

Homologous chromosome pairs are seperated and pulled to opposite poles of the cell

What happens in telophase 1 in meiosis?

The chromosomes reach the opposite poles of the cell where they uncoil, a nuclear envelope forms around each set of chromosomes and the nucleolus starts to reform, the cytoplasm divides to form two cells

What happens in prophase 2 in meiosis ?

The chromosomes condense and are now visible under a microscope. Centrioles migrate to opposite poles of the cell where each centriole starts forming spindle fibres, the nucleolus disappears and the nuclear envelope starts to break down

What happens in metaphase 2 in meiosis?

The chromosomes line up at the equator of the cell, each chromosome attaches to the spindle by their centromere

What happens during anaphase 2 in meiosis?

The centromeres divide and separate each pair of chromatids. The spindle fibres contract and shorten to pull the chromatids to opposite poles of the cell

What happens during telophase 2 in meiosis?

The chromatids reach the opposite poles of the cell where they uncoil to become long and thin again. A nuclear envelope forms each set of chromosomes to form two nuclei and the nucleolus starts to reform, the cytoplasm divides and 4 cells are produced

What are the two roles of meiosis?

Production of haploid gametes which allows for sexual reproduction. Creates genetic variation which increases diversity allowing for natural selection to take place

What is crossing over?

During prophase 1 the homologous chromosomes condense and pair up. The chromatids of each chromosome then twist around one another forming chiasmata. When the chromosomes are separated during anaphase 1 the chromatids break at the chiasmata and then reconnect to the chromatid from the homologous chromosome. This swaps alleles between the homologous chromosomes to produce different combinations on each chromosome

What is independent segregation (random assortment)?

Happens during metaphase 1 pairs of homologous chromosomes line up along the cell’s equator. However whether the paternal or maternal chromosomes appears on the left or right is completely random. As a result which chromosomes end up in each daughter cell is also random

How to calculate the number of genetically distinct gametes?

2^(number of chromosome pairs)

What is an allele?

A variant form of a gene

what are the 5 stages of natural selection?

1. There is variation in characteristics within a species

2. More genetic variation emerges within a population due to random mutations

3. Individuals with alleles that code for traits that are advantageous for survival are more likely to reproduce

4. These advantageous alleles are passed down to offspring

5. Over time these beneficial alleles become more common in the population

4 stages that bacteria become antibiotic resistant?

1. Some bacteria develop random mutations that provide resistance to antibiotics

2. When antibiotics are used only the resistant bacteria survive while the others die off

3. The resistant bacteria reproduce passing on resistant alleles to their offspring

4. Over time the proportion of resistant alleles increases leading to mostly resistant bacteria

What is directional selection?

Its favoured phenotype is extreme, on a normal distribution curve it shifts in the direction of the extreme, an example is antibiotic resistance in bacteria where the resistant bacteria survive and reproduce

What is stabilising selection?

Its favoured phenotype is average, on a normal distribution curve it narrows the curve, an example is human birth weight where infants of average weight have higher survival rates

What are adaptations?

Inherited characteristics that enhance an organisms ability to survive and reproduce in its specific environment

What are anatomical adaptations and4 examples?

The physical attributes that aid an organisms survival. Body coverings like fur and feathers protect organisms and support their survival, camouflage helps them to blend into their environment so less likely to be detected, mimicry where they imitate the appearance of more dangerous creatures for protection, teeth which are shaped to adapt to their diet

What are behavioural adaptations and 3 examples?

Actions that increase an organisms chances of survival and reproduction. Defensive responses like opossums play dead. Courtship displays such as male scorpions dance to attract a mate. Seasonal actions such as migration helps birds access resources year round

What are physiological adaptations and 3 examples?

Internal processes that give organisms an edge in survival. Venom used by snakes to immobilise prey. Antibiotics produced by bacteria to outcompete rival species. Water storage desert frogs can survive for over a year without a water source by storing water in their bodies