Topic 6: Inheritance, Variation & Evolution Many identical offspring produced when conditions are
Sexual & Asexual Reproduction: favourable
Sexual Reproduction
o Joining of male and female gametes (sperm and egg Organisms that sexually + asexually reproduce
or pollen and egg in flowering plants) Malarial parasites
o Mixing of genetic information leading to variety in o Reproduce sexually in mosquito
offspring o Haploid parasites in human produce asexually by
o Formation of gametes involving meiosis mitosis in the human host – in liver & blood cells
Asexual Reproduction o Female mosquito drinks blood containing these –
o Only one parent temperature drop makes them produce sexually –
o No fusion of gametes burst out of blood cells & fuse to form a diploid
o No mixing of genetic info zygote
o Genetically identical offspring – clones Some fungi
o Mitosis involved in making cells but bacteria o Spores produced asexually are genetically identical
reproduce by binary fission o Spores produced sexually when condition change in
Diploid vs. Haploid order to increase variation + avoid extinction
o Diploid cells have 2 sets of chromosomes (46 total) – Some plants
one set (23) from each parent o Reproduce sexually using pollen – must reach egg
o Haploid cells have 1 set of chromosomes (23 total) – cells in the female parts of another flower – called
only from one parent (gamete) pollination – forms seeds
Gametes o Strawberry plants reproduce asexually as they
o Gametes are formed by meiosis and are non-identical produce runner. New identical plants grow off the
therefore variation in offspring runners
o Daffodils reproduce sexually – grow from bulbs. New
Meiosis: bulb grow from the main one producing an identical
Cell division to produce 4 genetically different daughter plant
cells with half the genetic material of the parent o Advantageous in plants as it means they can
Meiosis only occur when gametes are made & the baby reproduce - even if flowers have been destroyed by
grows by mitosis after being a zygote frost or other animals
Key Points:
o Forms haploid cells DNA
o Produces 4 daughter cells Deoxyribonucleic Acid
o Used to make gametes Two long strands in a double helix spiral
o Produces cells with genetic variability A polymer – large molecules made up of repeating
o Produces cells with single set of chromosomes units called monomers
Method: o Made up of nucleotide so called polynucleotide as
o Diploid parent cell (100% DNA) well
o DNA is replicated / (chromosomes are copied) (200% o Each nucleotide is made up of a pentose sugar, a
DNA) phosphate and a base
o Cell splits into 2 genetically different daughter cells There are 4 bases (ATCG)
(100% DNA) o A and T are complementary
o 2 daughter cells split into a further two cells (50% o C and G are complementary
DNA) these are haploid A section of DNA (on a chromosome is
o Gametes (haploids) join at fertilisation to restore the called a gene)
normal number of chromosomes DNA is coiled up and stored in a chromosome
o Then the new cell (zygote) divides by mitosis Chromosomes are in the nucleus of the cell (23
Number of cells increases embryo develops pairs)
cells differentiate Order of nucleotides in the polymer creates a code
Because each gene codes for a specific sequence of
Sexual Reproduction Advantages amino acid this makes a specific protein (amino acid
Variation in offspring is the monomer of protein)
If environment changes, variation gives a survival Protein dependent on sequence order of bases
advantage by natural selection In mitosis, an enzyme breaks apart the two strands in
Natural selection can be sped up by humans in the helix spiral
selective breeding to increase food production Due to complementary base pairing a complementary
match can be created for each strand
Asexual Reproduction Advantages Sometimes there are mistakes during duplication = 20
Only one parent needed Any protein in the human body can be created from
More time efficient & energy efficient as only one arrangements of only 20 amino acids
parent needed
Faster than sexual reproduction The Genome
The entire genetic material of an organism
, Contains over 3 billion base pairings
Almost 21,000 genes coding for proteins
Differences across humans due to migration, ancestry,
disease
Importance of studying genome:
o Understand inherited disorders e.g. cystic fibrosis
& sickle cell disease & help scientists discover
medicines/ways to repair faulty genes
o Understand changes in genome when cancer
develops scientists & doctors can become even
better at choosing the best treatment for individuals
o Understand human evolution & history scientists Mutations
can trace human migration patterns from our ancient A random change in the DNA
history Random and continuous
o search for genes linked to different types of disease / Most do not alter the protein – they only alter is
understanding and treatment of inherited disorders / slightly so it’s appearance/function is not changed
use in tracing human migration patterns from the Not all parts of the DNA code for proteins
past Non-coding parts of the DNA can switch genes on & off
so variation in these areas of these DNA may affect the
Protein Synthesis way the genes are expressed
In ribosome of the cell DNA mutations change the amino acid sequence so a
DNA contains the instruction to make proteins different protein may be produced
The sequences of bases in the gene code for the If genes produce incorrect proteins cells may not
sequence of amino acids in a protein function properly cause inherited diseases
Types of proteins In a normal gene the substrate fits perfectly into the
o Enzyme active site of the enzymes
o Antibodies In mutated genes this could happen:
o Hormones o Enzyme almost unchanged active site works
o Structural bodies normally and reaction continues
DNA cannot escape the nucleus as its molecules are o Active site changes shape substrate doesn’t fit &
too large so it cannot go to the ribosomes – so uses enzyme doesn’t work
RNA – ribose nucleic acid o Active site changes shape different substrate fits &
o Small only 1 gene (1 strand) catalyses a different reactions
o Can escape nucleus Impacts of mutation
o Single stranded o Cause a change to amino acid being coded for
o AU CG (T does not exist so A is complementary to o Protein structure can be beneficial/harmful
base U) o Harmful mutations – non-functioning proteins results
Two stages Transcription & Translation in disease
o Transcription: The process by which DNA is read to Non-functioning enzymes – active site changes
produce a strand of mRNA shape
o Translation: The process by which mRNA is read to Cancer – cell division not controlled
produce a strand protein chain Cystic fibrosis/Sickle cell anaemia
Steps: o Beneficial – creates a new protein to enable natural
o An enzyme creates a copy of a gene onto a selection/evolution
complementary mRNA strand in the nucleus (Ts Protein of a different colour – for camouflage
become U) Protein for antibiotic resistance – bacteria survive
o The mRNA moves out of the nucleus and into the
ribosome because it is small enough to do so Inheritance
o The mRNA strand is read using triplet code. This Allele: Different forms of a gene (e.g. gene = eye colour
means every 3 bases code for 1 amino acid. and allele = brown, blue, hazel)
o tRNA (transport RNA) are carrier molecules. They Dominant: Allele that is always expressed, even is only
attach to the amino acids in the cytoplasm one copy is present
o On the other side the tRNA attaches to the base on Recessive: Allele that is only expressed if 2 copies are
the RNA (complementary and specific) present (& therefore no dominant)
o An enzyme links the amino acids together. Homozygous: A pair of chromosomes being made up of
o The tRNA detaches from the RNA, the protein 2 of the same alleles of a gene
detaches from the RNA & ribosome & folds into a Heterozygous: A pair of chromosomes being made up
unique shape to carry out is function of 2 different alleles of a gene
Gamete: A sex cell (egg/sperm)
Zygote: Formed when a sperm fertilises an egg
Phenotype: Physical expression of a trait
Genotype:
Sexual & Asexual Reproduction: favourable
Sexual Reproduction
o Joining of male and female gametes (sperm and egg Organisms that sexually + asexually reproduce
or pollen and egg in flowering plants) Malarial parasites
o Mixing of genetic information leading to variety in o Reproduce sexually in mosquito
offspring o Haploid parasites in human produce asexually by
o Formation of gametes involving meiosis mitosis in the human host – in liver & blood cells
Asexual Reproduction o Female mosquito drinks blood containing these –
o Only one parent temperature drop makes them produce sexually –
o No fusion of gametes burst out of blood cells & fuse to form a diploid
o No mixing of genetic info zygote
o Genetically identical offspring – clones Some fungi
o Mitosis involved in making cells but bacteria o Spores produced asexually are genetically identical
reproduce by binary fission o Spores produced sexually when condition change in
Diploid vs. Haploid order to increase variation + avoid extinction
o Diploid cells have 2 sets of chromosomes (46 total) – Some plants
one set (23) from each parent o Reproduce sexually using pollen – must reach egg
o Haploid cells have 1 set of chromosomes (23 total) – cells in the female parts of another flower – called
only from one parent (gamete) pollination – forms seeds
Gametes o Strawberry plants reproduce asexually as they
o Gametes are formed by meiosis and are non-identical produce runner. New identical plants grow off the
therefore variation in offspring runners
o Daffodils reproduce sexually – grow from bulbs. New
Meiosis: bulb grow from the main one producing an identical
Cell division to produce 4 genetically different daughter plant
cells with half the genetic material of the parent o Advantageous in plants as it means they can
Meiosis only occur when gametes are made & the baby reproduce - even if flowers have been destroyed by
grows by mitosis after being a zygote frost or other animals
Key Points:
o Forms haploid cells DNA
o Produces 4 daughter cells Deoxyribonucleic Acid
o Used to make gametes Two long strands in a double helix spiral
o Produces cells with genetic variability A polymer – large molecules made up of repeating
o Produces cells with single set of chromosomes units called monomers
Method: o Made up of nucleotide so called polynucleotide as
o Diploid parent cell (100% DNA) well
o DNA is replicated / (chromosomes are copied) (200% o Each nucleotide is made up of a pentose sugar, a
DNA) phosphate and a base
o Cell splits into 2 genetically different daughter cells There are 4 bases (ATCG)
(100% DNA) o A and T are complementary
o 2 daughter cells split into a further two cells (50% o C and G are complementary
DNA) these are haploid A section of DNA (on a chromosome is
o Gametes (haploids) join at fertilisation to restore the called a gene)
normal number of chromosomes DNA is coiled up and stored in a chromosome
o Then the new cell (zygote) divides by mitosis Chromosomes are in the nucleus of the cell (23
Number of cells increases embryo develops pairs)
cells differentiate Order of nucleotides in the polymer creates a code
Because each gene codes for a specific sequence of
Sexual Reproduction Advantages amino acid this makes a specific protein (amino acid
Variation in offspring is the monomer of protein)
If environment changes, variation gives a survival Protein dependent on sequence order of bases
advantage by natural selection In mitosis, an enzyme breaks apart the two strands in
Natural selection can be sped up by humans in the helix spiral
selective breeding to increase food production Due to complementary base pairing a complementary
match can be created for each strand
Asexual Reproduction Advantages Sometimes there are mistakes during duplication = 20
Only one parent needed Any protein in the human body can be created from
More time efficient & energy efficient as only one arrangements of only 20 amino acids
parent needed
Faster than sexual reproduction The Genome
The entire genetic material of an organism
, Contains over 3 billion base pairings
Almost 21,000 genes coding for proteins
Differences across humans due to migration, ancestry,
disease
Importance of studying genome:
o Understand inherited disorders e.g. cystic fibrosis
& sickle cell disease & help scientists discover
medicines/ways to repair faulty genes
o Understand changes in genome when cancer
develops scientists & doctors can become even
better at choosing the best treatment for individuals
o Understand human evolution & history scientists Mutations
can trace human migration patterns from our ancient A random change in the DNA
history Random and continuous
o search for genes linked to different types of disease / Most do not alter the protein – they only alter is
understanding and treatment of inherited disorders / slightly so it’s appearance/function is not changed
use in tracing human migration patterns from the Not all parts of the DNA code for proteins
past Non-coding parts of the DNA can switch genes on & off
so variation in these areas of these DNA may affect the
Protein Synthesis way the genes are expressed
In ribosome of the cell DNA mutations change the amino acid sequence so a
DNA contains the instruction to make proteins different protein may be produced
The sequences of bases in the gene code for the If genes produce incorrect proteins cells may not
sequence of amino acids in a protein function properly cause inherited diseases
Types of proteins In a normal gene the substrate fits perfectly into the
o Enzyme active site of the enzymes
o Antibodies In mutated genes this could happen:
o Hormones o Enzyme almost unchanged active site works
o Structural bodies normally and reaction continues
DNA cannot escape the nucleus as its molecules are o Active site changes shape substrate doesn’t fit &
too large so it cannot go to the ribosomes – so uses enzyme doesn’t work
RNA – ribose nucleic acid o Active site changes shape different substrate fits &
o Small only 1 gene (1 strand) catalyses a different reactions
o Can escape nucleus Impacts of mutation
o Single stranded o Cause a change to amino acid being coded for
o AU CG (T does not exist so A is complementary to o Protein structure can be beneficial/harmful
base U) o Harmful mutations – non-functioning proteins results
Two stages Transcription & Translation in disease
o Transcription: The process by which DNA is read to Non-functioning enzymes – active site changes
produce a strand of mRNA shape
o Translation: The process by which mRNA is read to Cancer – cell division not controlled
produce a strand protein chain Cystic fibrosis/Sickle cell anaemia
Steps: o Beneficial – creates a new protein to enable natural
o An enzyme creates a copy of a gene onto a selection/evolution
complementary mRNA strand in the nucleus (Ts Protein of a different colour – for camouflage
become U) Protein for antibiotic resistance – bacteria survive
o The mRNA moves out of the nucleus and into the
ribosome because it is small enough to do so Inheritance
o The mRNA strand is read using triplet code. This Allele: Different forms of a gene (e.g. gene = eye colour
means every 3 bases code for 1 amino acid. and allele = brown, blue, hazel)
o tRNA (transport RNA) are carrier molecules. They Dominant: Allele that is always expressed, even is only
attach to the amino acids in the cytoplasm one copy is present
o On the other side the tRNA attaches to the base on Recessive: Allele that is only expressed if 2 copies are
the RNA (complementary and specific) present (& therefore no dominant)
o An enzyme links the amino acids together. Homozygous: A pair of chromosomes being made up of
o The tRNA detaches from the RNA, the protein 2 of the same alleles of a gene
detaches from the RNA & ribosome & folds into a Heterozygous: A pair of chromosomes being made up
unique shape to carry out is function of 2 different alleles of a gene
Gamete: A sex cell (egg/sperm)
Zygote: Formed when a sperm fertilises an egg
Phenotype: Physical expression of a trait
Genotype:
