Topic 4 Genetic Code, Meiosis, Biodiversity and Natural selection

Describe the differences between eukaryotic DNA and Prokaryotic DNA

What is the definition of a ‘gene’

A sequence of DNA bases that code for a polypepetide or a functional RNA molecule

What is the definition of a ‘locus’

Location of the gene on a chromosome

What is a triplet code?

A sequence of three DNA bases that codes for a specific amino acid

If I had a polypeptide chain that contains 20 amino acids how many DNA bases where needed to code for it?

3×20=60

How many chromosomes do humans have?

46

How many pairs of chromosomes do humans have?

23

How is DNA arranged in a chromosome

DNA is tightly coiled around histones

What are the three features of the genetic code?

1. Degenerate

2. Universal

3. Non-Overlapping

What does Degenerate mean

more than one triplet can code for the same amino acid

Why is the degeneracy of the genetic code an advantage?

Of a mutation occurs in one of the DNA bases

it may still code for the same amino acid

Therefore have no effect

what does it mean when the genetic code is Universal?

The same triplet code will code for the same amino acid in ALL organisms

What does Non-Overlapping mean in the genetic code

Each base is only part of one triplet

(No overlapping in bases)

Why is non-overlapping advantageous?

If a mutation occurs it will only affect one codon

Therefore only one amino acid will be affected

What are introns and exons in DNA?

Introns- non coding sequences of DNA

Exons- sequences of DNA that code for amino acids

What is the definition of a codon?

The three bases on mRNA That code for a specific amino acid

What is the definitions of a start and stop codon?

Start codon- three bases at the start of every gene that initiate translation

Stop codon- three bases at the end of every gene that causes the ribosome to detach and stop translation

Define Genetic code

The sequence of dna bases that codes for amino acids in polypeptides

Describe the differences between prokaryotic and eukaryotic DNA (5 marks)

Prokaryotic DNA is found in the cytoplasm

Eukaryotic DNA is found in the nucleus

Eukaryotic DNA is linear

Prokaryotic DNA is circular

Eukaryotic DNA contains introns while prokaryotic DNA doesn’t

Prokaryotic cells contain plasmids which are small circular DNA molecules, while eukaryotic cells do not.

Eukaryotic DNA is associated with histones

What is a pair of homologous chromosomes (2 marks)

2 chromosomes that carry the same genes

At the same loci

What is the definition of a genome

An organisms complete set of DNA in a cell

What is the definition of a proteome

Is the full range of proteins that a cell is able to produce

What bases are found in DNA?

Adenine, thymine, guanine and cytosine

What bases are found in RNA?

Uracil, thymine, guanine and cytosine

Where is mRNA found in and how is it made?

Found in the cytoplasm and nucleus

Made in transcription in the nucleus from the DNA sequence

How old is the structure of DNA different to mRNA?

DNA is double-stranded wall mRNA a single stranded

DNA from the double helix structure whilst mRNA is linear

DNA contains deoxyribose sugar while mRNA contains ribose sugar

DNA contains thymine while mRNA contains uracil instead

DNA has hydrogen bonds between complementary base pairs. MRNA does not.

DNA contains triplets and mRNA contains codons.

Where is tRNA found in, and what is it involved in?

found in the cytoplasm

Involved in translation, and it has an amino acid binding site

Describe the structure of a tRNA molecule

Has an amino acid binding site that is specific

A single stranded polynucleotide that is folded in a clover leaf shape

It has Hydrogen bonds between base pairs to hold it shape

It has anticodons which are complementary to mRNA codons

What are the 2 stages in protein synthesis?

Transcription and translation

Describe the process of transcription (5 marks)

Hydrogen bonds between the DNA bases break, causing the DNA double helix to separate into two template strands with exposed bases

One DNA strand is used as template

Free RNA nucleotides are attracted to their complimentary bases by complimentary base pairing

RNA Uracil base pairs pair with adenine DNA bases

RNA Polymerase catalases the condensation reaction to form phosphodiester bonds between adjacent RNA nucleotides together

Creating Pre-mRNA which is then spliced (removing introns) to form mRNA

Describe what occurs after transcription in order to turn pre-mRNA into mRNA

pre-mRNA is spliced to remove the introns

Why doesn’t splicing occur in Prokaryotic mRNA?

prokaryotic DNA does not contain introns

Describe the process of translation (6 marks)

mRNA attaches to the ribosome

tRNA anticodons bind to complimentary mRNA codons

tRNA molecules bring specific amino acids coded for by the specific mRNA codons

Adjacent amino acids are joined together by phosphodiester bonds using ATP

tRNA is released after the amino acids join to form a polypeptide

The ribosome moves along the mRNA strand to form a polypeptide

What are the three ways genetic variation can be introduced?

Meiosis

Mutations

Radom fertilisation of gametes

Describe the process of meiosis

What are the differences between meiosis and mitosis?

Meiosis- produces 4 haploid cells, Mitosis creates 2 diploid cells

Meiosis- has 2 nuclear divisions, Mitosis has 1

Meiosis- introduce genetic variation, Mitosis creates genetically identical cells

Describe the process of independent segregation in meiosis 1

Happens in Meiosis 1

When the homologous chromosomes line up opposite each other at the equator

And it is random on which side is the paternal and maternal chromosome lie

What is the formula to work out the different combinations of the homologous pairs.

2^n

n= number of homologous pairs

Describe the process of crossing over in meiosis 1

Definition of a gene mutation

Is the change in the base sequence of DNA, which is random and occurs in DNA replication

What increases the likelihood of a genetic mutation?

Exposure to cancer causing agents

Such as UV, and radiation

What 2 types of genetic mutation are there?

Substitution

Deletion

Why is a deletion of a DNA base worse than a substitution of a base?

Substituting a base may still allow the new codon to still code for the same amino acid due to the genetic code being degenerate

Deleting a base can cause a frame shift. Which changes all the codons to incorrectly code for the wrong amino acids

What mutation can occur in meiosis?

Non-disjunction In meiosis 1

The homologous chromosome do not separate equally

Meiosis 2 the sister chromosomes don’t separate equally

What does non-disjunction cause?

Where the haploid cells receiving extra chromosomes or too few chromosomes

What is the definition of genetic diversity?

The number of different alleles in a population

What is the definition of a gene pool

All the genes and alleles in a population at a particular time

What is the definition of allele frequency?

Is the proportion of organisms within the population carrying a particular allele

Describe the process of natural selection

Directional selection

When a change in the environment occurs

Causing the modal trait to move to one extreme

Stabilising selection

No change in the environment

The modal trait has a selective advantage

Individuals which have other traits decrease,

standard deviation decreases

Mutation results in a new allele

Individuals with the allele are able to digest triglycerides

And are more likely to survive and reproduce

Their offspring will inherit the allele

Directional selection occurs over many generations

and the allele frequency increases in the population

Definition of a species

Two organisms that belong to the same species and able to breed and produce fertile offspring

What type of adaption is Courtship behaviour?

Behavioural adaptation

That is essential for successful mating and species recognition

For survival

Describe what courtship behaviour is

The different behaviours that animals demonstrate to attract a mate. Each species demonstrates it own unique behaviour

This is essential for successful mating

What is an advantage of Courtship?

To recognise members of the same species and opposite sex

Only occurs when both males and females are sexually mature.

Males will only dance when releasing gametes

Females will only respond to the males when releasing eggs

Why can courtship rituals ensure the survival of the offspring?

Form a pair bond between the parents

Choose a strong and healthy mate

How are organisms named using the Binomial Naming System?

genus species

Phylogenetic trees

Arranges species into groups according to evolutionary origin and relationships

What can phylogeny tell us?

How closely related species are. And if they share a common ancestor

What is the order in classification

Definition for species richness

The number of different species in a community

Definition of index of diveristy

The number of different species and the number of individuals in each species

Explain how allopathic speciation can form a new species

Physical barrier,

No gene flow

Mutation occurs causing genetic variation

Different environments causes different selection pressures

The mutation causes an advantageous allele to occur, which is then passed on the next generation

Overtime the two groups of species cannot interbreed and produce fertile offspring anymore