genetics and relationships

What is the structure of a chromosome

It is two sister chromatids joined at the centromere and its two since the DNA has been replicated

Describe the structure of DNA

• Polynucleotide

• Nucleotide contains deoxyribose sugar, nitrogenous base and phosphate groups

• Joined by phosphodiester bonds

• Double helix shaped due to hydrogen bonds forming base pairs

• A with T and C with G

• DNA associated with histones

What is DNA normally in the form in interphase

Chromatin

What are homologous chromosomes

They carry the same gene at the same loci but not necessarily the same alleles and they come in pairs

What is an allele

A version of a gene

What is a gene

A base sequence of DNA that codes for an amino acid sequence of a polypeptide or a functional RNA

What is a triplet code

3 bases code for each amino acid

Why is the universal code degenerate

Most amino acids have more than one triplet code

Why is the universal code universal

the same triplet always codes for the same amino acid in mostly all organisms

Why is the genetic code non overlapping

Each base is read only once and is part of only one codon

What is an intron

Non coding section of DNA

What is an exon

Coding section within a gene that codes for an amino acid

What is a proteome

All proteins the cell is able to produce

What is a genome

All the different genes present within a cell

What is transcription

DNA copied in to an mRNA molecule

What is translation

mRNA code converted to polypeptide

Explain the transcription

• RNA polymerase attaches to a gene and moves down molecule

• This breaks hydrogen bonds between bases

• One strand acts as a template as free RNA nucleotides align by hydrogen bonds and thymine replaced with uracil

• RNA polymerase then joins adjacent nucleotides by phosphodiester bonds, forming pre-mRNA

• pre mRNA is spliced to remove introns and form mRNA

• MRNA detaches and leaves nucleus via nuclear pores to cytoplasm

Explain translation

• mRNA attaches to the ribosome and reads 2 codons at a time

• tRNA anticodon binds to complimentary codon

• This then brings a specific amino acid

• The 2nd tRNA binds and the process is the same

• The amino acids are joined together by peptide bonds via a condensation reactions using ATP

• The tRNA is released and the ribosome moves along the mRNA until the stop codon

What is a mutation

A change in base sequence of DNA which forms new alleles creating variation

When does mutation happen

• DNA replication due to exposed baes

  • Increased by mutagenic agents such as UV

What is a substitution mutation

One base replaced with another

What are the consequences of the substitution

• as the genetic code is degenerate, the same amino acid may be coded for

• However, it could result in a different amino acid or a stop codon so an incorrect sequence

What is a deletion mutation

A base is removed

What is the consequences of the deletion mutation

It causes a frame shift as it changes each triplet after the deletion causing a different amino acid sequence

What is meiosis

Cell division that involves 2 nuclear divisions forming 4 haploid daughter cells from one parent diploid cell

What introduces variation in meiosis

• independent segregation

• Crossing over

  • Occurs in meiosis 1

Describe the process of meiosis

• DNA replication occurs and the chromosomes double

• Then meiosis 1 occurs and the homologous pairs separate which halves the number of chromosomes into 2 cells

• Then meiosis 2 occurs which causes the chromatids to separate into 2 cells each for a total of 4 haploid cells

What is independent segregation

Homologous chromosomes will line up differently each time so there will be a random separation of the chromosomes

How to calculate the number of different combinations of chromosomes in gametes in independent segregation

2^n where n is the number of homologous pairs

What is crossing over

• when homologous pairs line up, the chromatids could become twisted around each other forming a chiasmata

• This causes equal lengths of chromatids to be exchanged

• This causes a new combination of alleles

What increases variation after meiosis

• random fusion of gametes (fertilisation)

  • (2^n)²

What is the example of chromosome mutation

Non disjunction in meiosis

What is non disjunction

• chromosomes fail to separate properly in meiosis 1

• Chromatids fail to separate properly in meiosis 2

What is the effect of non disjunction

The resulting gametes will not have the correct number of chromosomes

What is genetic diversity

Number of different alleles of a gene in a population

What is evolution

Change in allele frequency over many generations in a population

What are genetic reasons of variation

• random mutations

• Meosis

• Random fusion of gametes

What are environmental reasons of variation

• climatic change

• Food availability

• Disease

What are the three different types of ways animals are adapted

• anatomical

• Physiological

• Behavioural

Explain natural selection

• random mutations result in new alleles forming

• Some mutations give rise to beneficial alleles which increases the organisms chance to survive and it increases reproductive success

• Advantageous aleles inherited by next generation

• Over many generations, the allele frequency increases

Explain antibiotic resistance

• mutations gives new alleles which gives some individuals resistance

• Resistant ones survive when the antibiotic is introduced so increases reproductive rate by binary fission passing on resistance alleles

• Resistant alleles increase within a population

Why is antibiotic resistance a problem in hospitals

Due to high exposure of bacteria so antibiotics commonly used

What is directional selection

One of the extremes has a selective advantage occurring when there is a change in environment

• this leads to the modal trait changing as the organisms on one extreme with the alleles which increases survival rate have a higher reproductive success and will pass on that advantageous allele and over many generations, the allele frequency will increase

Why is it called directional selection

Selective pressure will make the mean move to one extreme

What is stabilising selection

• the modal trait has the selective advantage occurring when there is no change in the environment so modal trait remains the same

• Standard deviation decreases as individuals with the extreme trait decrease

What is a species

Similar organisms that can reproduce to give fertile offspring and occupy the same ecological niche

How is an organism named

Via the binomial system Genus species

What are the three domains

• Archaea

• Prokaryotic

• Eukaryotic

What is the classification system

• Domain

• kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

  • Each group is a taxa

Why is the classification system a hierarchy

• smaller groups arranged within larger groups

• With no overlap between groups

Ways of classifying organism

• DNA sequence

• MRNA sequence

• Amino acid sequence

• Immunological - comparing similarity in self antibody shape

What is phylogenetic classification

Grouping organisms according to their evolutionary organisms and relationships, showing how closely related

How are organisms classified into a phylogenetic classification system

via a hierarchy of groups with no overlap with a common ancestor

What is courtship

Used to attract a mate of the right species which is capable of breeding to make fertile offspring

What are examples of courtship

• releasing pheromones

• Visual displays

• Nest building

Why is courtship behaviour important for mating

As similar species exhibit the sae behaviour and the more closely related the species are ,the more similar the species

What are the benefits of courtship

• finds healthy mate

• Forms a pair bond so offspring can be successfully raised

• Synchronise mating so max chance of fertilisation

What is biodiversity

Range of different species in a particular region

What is species richness

The measure of different species in a community

What is the index of diversity

The relationship between the number of species and the number of individuals of each species

How do you calculate index of diversity

D = N(N-1)/ sum of n(n-1)

What is a habitat

The place where an organism lives

What is a population

The number of organisms of the same species in the same habitat at a specific time

What is a community

All the populations of different species in a habitat

Why has there been a recent decrease in biodiversity

Human activity

What are the main 5 reasons of the reduction of biodiversity

• destruction of hedgerows

• Selective breeding

• Monocultures

• Over grazing

• Filling in / draining ponds

Why is the destruction of hedgerows harmful

Habitat to many species so destroying them reduces species richness and forces migration

Why is selective breeding harmful

It reduces genetic diversity as there are now fewer alleles present and this could lead to high vulnerability against sudden environmental change

Why are monocultures harmful

Low genetic diversity and it an only support few organisms which further reduces biodiversity

Why is a compromise between farming and biodiversity needed

Farming produces food for humans and biodiversity produces new sources of food and medicine and benefits insects via pollination

What are the methods of compromises

• protecting endangered species

• Protected areas from further development

• Encourages farming practice that conserve biodiversity Such as replanting hedgerows

What is aseptic technique

Prevents the contamination of microbes

What are the methods of aseptic technique

• sterilised work surfaces and all equipment via disinfectants and Bunsen burner

• Wash hands with soap to remove microbe

• Work near Bunsen burner to have convection current sterilising air

• Only open Petri dish slightly

• Run the mouth of the broth bottle over the Bunsen burner

How do you make a culture of bacteria

• open dish lid slightly and add bacteria to the dish

• Spread using a sterile spreader

• Place antibiotics in the dish

• Incubate at 25C for 48 hours

• Measure zone of inhibition using vernier callipers and the larger the zone of inhibition, the better the effect of the antibiotic