B6 - Inheritance, Variation and Evolution

Know the bases detailed diagrams, know the detailed DNA structure and mRNA (exam answer), speciation diagrams, genetic engineering diagram, mitosis & meiosis diagram, know the classification

DNA (DeoxyriboNucleic Acid)

contains coded instructions on how to make the organism work

List the parts of the DNA structure in order from smallest to largest

DNA, gene, chromosome, nucleus

gene

small section of DNA coding for a sequence of amino acids which form a specific protein (20 amino acids which code for thousands of proteins)

genome (understanding this helps understand genetic/ inherited diseases and understand evolution)

entire set of genetic material in an organism

What are the base pairs in the structure of DNA?

AT, CG

Ribosomes

Site of protein synthesis

Nucleus

Where DNA is stored

Enzymes

Biological catalysts to speed up chemical reactions

Hormones

Carry messages around the body

Structural proteins

Physically strong

Mutation

Random genetic change, can be inherited, happen continuously/spontaneously, can change the shape of an active site so the substrate can no longer bond

Insertion

New base, changes the way bases are ‘read’, knock-on effect

Deletion

Random base deleted, knock-on effect

Substitution

Base randomly changed, no knock-on effect

Sexual reproduction

Fusion of male and female gametes

How are gametes produced?

Meiosis

Egg + sperm fuse =

Fertilisation

Asexual reproduction

Offspring are genetically identical to parent and each other

How are asexually reproduced offspring produced?

Mitosis

What are pros of sexual reproduction?

Variation (species more likely to survive), selective breeding is possible (choose desired characteristics)

What are cons of sexual reproduction?

More energy, slower

What are pros of asexual reproduction?

Less energy (no need for a mate), faster

What are cons of asexual reproduction?

Limited gene pool

How does malaria reproduce?

Sexually in the mosquito, asexually in the human

How does fungus reproduce?

Sexually in unfavourable conditions to increase variation

How do plants’ seeds reproduce?

Asexually to produce bulbs, sexually in normal growth

What sexes have X or Y chromosomes?

Males - XY, Females - XX

Alleles

Different versions of a gene, one on each chromosome

Homozygous

2 of same allele

Heterozygous

2 different alleles

Recessive

Needs 2 alleles to be expressed

Dominant

Needs 1 allele to be expressed

Phenotype

Pair of alleles

What does a punnet square showing an XY father and a XX mother show?

50% chance of male offspring, 50% chance of female offspring

Cystic fibrosis (recessive)

Production of thick mucus in air passages

Polydactyly (dominant)

Extra fingers/toes

Embryonic screening

In IVF, it is possible to remove a cell from an embryo and analyse it for genetic disorders

Pros of embryonic screening

Prevents suffering, expensive to treat disorders, there are laws to keep it under control

Cons of embryonic screening

Increases prejudice against disabled people, expensive, human selective breeding

Mendel conclusions

Plant characteristics are determined by hereditary units, hereditary units are passed onto offspring, hereditary units can be dominant or recessive

Variation

Happens because of mutations and because offspring do not inherit all their genes from one parent

Genetic variation

Eye colour, blood group, inherited disorders

Environmental variation

Scars, tattoos, suntan, limb loss,

Both variation

Weight, height, skin tone, teeth, intelligence, athleticism

Evolution

The theory that all modern species evolved from simpler life forms 3 billion years ago

Jean-Baptise Lamarck

Argued that acquired changes over and organism’s life would pass onto offspring

Charles Darwin

Used experiments, fossils and geology to suggest natural selection

Natural selection

The theory that organisms with more advantageous characteristics are more likely to survive and reproduce (over time, this leads to evolution)

Speciation

Where two groups of the same species evolve apart so much that they can no longer produce fertile offspring together

Objections to Darwin

Religious beliefs (the creator), he could not explain how these characteristics appeared or were passed on, not enough evidence

Selective breeding

Where humans artificially select organisms with desired characteristics and breed them together

Examples of selective breeding

Animals that produce more meat or milk, crops with disease or herb/pesticide resistance, gentle dogs or cats, pretty flowers on plants

Selective breeding steps

1. Select organisms with desired characteristics

2. Breed them together

3. Select the offspring with the best characteristics and breed them together

4. Repeat the process until the offspring all have the desired characteristic

Drawback of selective breeding

Reduced gene pool

Reduced gene pool

Increased chance of genetic disorder, decreased chance of immunity genes

Genetic engineering steps

1. Useful gene is cut from the genome using enzymes

2. Inserted into a vector (bacterial plasmid or virus)

3. Useful gene is inserted into the target organism’s cells

Pros of genetic engineering

Increased yield, increased nutrients, already is working

Cons of genetic engineering

Impact biodiversity, unsure about safety, could affect genes of surrounding plants

Tissue culture

A few plant cells put in a growth medium with hormones, grow into clones of parent plant, very quick, little space, preserves rare plants

Cuttings

Take cuttings from good parent plant, plant to produce plants, very quick, very cheap, established method

Embryo transplants

Sperm and egg are taken from a bull and cow, artificial fertilisation then split the embryo among many cows, the calves are identical

Adult cell cloning

Take an unfertilised egg cell and remove its nucleus, nucleus is taken from adult body cell and inserted into egg cell, egg is stimulated by an electric shock, making it divide like an embryo, the embryo is implanted into an adult female and grows like a normal foetus

Pros of adult cell cloning

Many ideal offspring, greater understanding of age, preserve endangered species

Cons of adult cell cloning

Reduced gene pool, not as healthy, ethics (suffering)

Gradual replacement by minerals (fossils)

Teeth, shells and bones take a long time to decay, they are replaced by minerals as they decay, so the shape remains distinct

Casts and impressions (fossils)

When an organism is buried in soft material and the material hardens, a cast is left behind (burrows or footprints)

Preservation

Sometimes animals die in amber, ice or peat bogs, so don’t decay

Steps of speciation

1. Two populations of the same species

2. Populations are isolated by a physical barrier

3. Populations undergo natural selection in different environments

4. Populations evolve until they can no longer produce fertile offspring with each other

Anti biotic resistance

Anti-biotic create a situation where resistant bacteria have an advantage, anti-biotics mutate to become resistant to anti-biotics