Inheritance, Variation and Evolution
Sexual and asexual reproduction
Sexual and Asexual Reproduction:
- Sexual reproduction involves the fusion of male and female gametes. meiosis
Because there are two parents, the offspring contain a mixture of their DNA
parents’ genes.
Protein synthesis
- In asexual reproduction there’s only one parent. There’s no fusion of
gametes, no mixing of chromosomes and no genetic variation between the Mutations
parent and the offspring. The offspring are genetically identical to the Genetic inheritance
parent – they’re clones
Genetic disorders
- Some organisms can reproduce both sexually and asexually depending on
the conditions Variation
o Malaria reproduces sexually when it’s in a mosquito and asexually Selective breeding
when it’s in a human host Genetic engineering
o Fungi release spores which can become new fungi when they
land in a suitable pace. Spore can be produced sexually and Cloning
asexually. Evolution
o Plant produce seeds sexually, but some can also reproduce Speciation
asexually e.g. strawberry plants produce runners. These are stems
Evidence for evolution
that grow horizontally on the surface of the soil away from a
plant. At various points along the runner, a new strawberry extinction
plant forms that is identical to the original plant. Another example is plants that grow from
bulbs. New bulbs can form from the main bulb and divide off. Each new bulb can grow into a
new identical plant.
Sexual Asexual
Number of 2 1
parents
Type of division Meiosis Mitosis
Advantages - Produces variation in the - Only 1 parent needed.
offspring - More time and energy efficient
- If the environment changes - No need to find a mate
variation gives a survival - Faster
advantages for the species by - Many genetically identical offspring
natural selection. produced in favourable conditions
- Selective breeding by humans (can spread/colonise an area)
can speed up the process of - If one is well adapted to habitat, all
natural selection. Increased food will be
production.
Meiosis:
- Gametes are formed by meiosis; they only have one copy of each chromosome so that when gamete
fusion happens, they have the right amount again.
- Meiosis contains 2 divisions and in humans it only happens in the reproductive organs.
o Before the cell starts to divide, it duplicates its genetic information, forming two armed
chromosomes – one arm of each chromosome is an exact copy of the other arm. After
replication, the chromosomes arrange themselves into pairs.
o In the first division in meiosis the chromosome pairs line up in the centre of the cell.
1
, o The pairs are then pulled apart, so each new cell only has one copy of each chromosome. Some
of both the mother’s and father’s chromosomes go into each cell.
o In the second division, the chromosomes line up again in the centre of the cell. The arms of the
chromosomes are pulled apart.
- You get 4 gametes, each with only a single set of chromosomes in it. Each of the gametes is genetically
different from the others because the chromosomes all get shuffled up during meiosis and each gamete
only gets half of them.
Mitosis Meiosis
Roles within living organisms Growth To produce gametes
Repair
Asexual reproduction
Where it occurs All body cells In the gonads
Number of divisions 1 2
Chromosome number in Same Half
daughter cells compared to
parent cell
Genetic similarity of daughter Identical Genetically different
cells to parent cells
Number of daughter cells 2 4
DNA:
- DNA stands for deoxyribonucleic acid. It’s the chemical that all of the genetic material in a cell is made
up from.
- The DNA is contained in chromosomes. A gene is a small section of. DNA on a chromosome. Each gene
codes for a particular sequence of amino acids, to make a specific protein. Only 20 amino acids are
used, but they make up thousands of different proteins
- The genome of an organism is its entire genetic material. Understanding the human genome is a really
important tool for science and medicine for many reasons.
o It allows scientist to identify genes in the genome that are linked to different types of disease.
o Knowing which genes are linked to inherited diseases could help us to understand them better
and could help us to develop effective treatments for them.
o Scientists can investigate how humans may have changed over time, and even how ancient
populations may have migrated across the globe.
- DNA strands are polymers made up of lots of repeating units called nucleotides. Each nucleotide
consists of one sugar molecule, one phosphate molecule and one base.
- The sugar and phosphate molecules in the nucleotides form a backbone to DNA strands. The sugar and
phosphate molecules alternate. One of four different bases – A, T, C and G joins to each sugar. Each
base links to a base on the opposite strand in the helix. (A with T, C with G).
- It’s the order of bases in a gene that decides the order of amino acids in a protein. Each amino acid is
coded for by a sequence of 3 bases in the gene.
- The amino acids are joined together to make various proteins.
- There are parts of DNA that don’t code for proteins. Some of these non-coding parts switch genes on
and off, so they control whether or not a gene is expressed (used to make a protein).
Protein Synthesis:
- Proteins are made in the cell cytoplasm on tiny structure called ribosomes.
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Sexual and asexual reproduction
Sexual and Asexual Reproduction:
- Sexual reproduction involves the fusion of male and female gametes. meiosis
Because there are two parents, the offspring contain a mixture of their DNA
parents’ genes.
Protein synthesis
- In asexual reproduction there’s only one parent. There’s no fusion of
gametes, no mixing of chromosomes and no genetic variation between the Mutations
parent and the offspring. The offspring are genetically identical to the Genetic inheritance
parent – they’re clones
Genetic disorders
- Some organisms can reproduce both sexually and asexually depending on
the conditions Variation
o Malaria reproduces sexually when it’s in a mosquito and asexually Selective breeding
when it’s in a human host Genetic engineering
o Fungi release spores which can become new fungi when they
land in a suitable pace. Spore can be produced sexually and Cloning
asexually. Evolution
o Plant produce seeds sexually, but some can also reproduce Speciation
asexually e.g. strawberry plants produce runners. These are stems
Evidence for evolution
that grow horizontally on the surface of the soil away from a
plant. At various points along the runner, a new strawberry extinction
plant forms that is identical to the original plant. Another example is plants that grow from
bulbs. New bulbs can form from the main bulb and divide off. Each new bulb can grow into a
new identical plant.
Sexual Asexual
Number of 2 1
parents
Type of division Meiosis Mitosis
Advantages - Produces variation in the - Only 1 parent needed.
offspring - More time and energy efficient
- If the environment changes - No need to find a mate
variation gives a survival - Faster
advantages for the species by - Many genetically identical offspring
natural selection. produced in favourable conditions
- Selective breeding by humans (can spread/colonise an area)
can speed up the process of - If one is well adapted to habitat, all
natural selection. Increased food will be
production.
Meiosis:
- Gametes are formed by meiosis; they only have one copy of each chromosome so that when gamete
fusion happens, they have the right amount again.
- Meiosis contains 2 divisions and in humans it only happens in the reproductive organs.
o Before the cell starts to divide, it duplicates its genetic information, forming two armed
chromosomes – one arm of each chromosome is an exact copy of the other arm. After
replication, the chromosomes arrange themselves into pairs.
o In the first division in meiosis the chromosome pairs line up in the centre of the cell.
1
, o The pairs are then pulled apart, so each new cell only has one copy of each chromosome. Some
of both the mother’s and father’s chromosomes go into each cell.
o In the second division, the chromosomes line up again in the centre of the cell. The arms of the
chromosomes are pulled apart.
- You get 4 gametes, each with only a single set of chromosomes in it. Each of the gametes is genetically
different from the others because the chromosomes all get shuffled up during meiosis and each gamete
only gets half of them.
Mitosis Meiosis
Roles within living organisms Growth To produce gametes
Repair
Asexual reproduction
Where it occurs All body cells In the gonads
Number of divisions 1 2
Chromosome number in Same Half
daughter cells compared to
parent cell
Genetic similarity of daughter Identical Genetically different
cells to parent cells
Number of daughter cells 2 4
DNA:
- DNA stands for deoxyribonucleic acid. It’s the chemical that all of the genetic material in a cell is made
up from.
- The DNA is contained in chromosomes. A gene is a small section of. DNA on a chromosome. Each gene
codes for a particular sequence of amino acids, to make a specific protein. Only 20 amino acids are
used, but they make up thousands of different proteins
- The genome of an organism is its entire genetic material. Understanding the human genome is a really
important tool for science and medicine for many reasons.
o It allows scientist to identify genes in the genome that are linked to different types of disease.
o Knowing which genes are linked to inherited diseases could help us to understand them better
and could help us to develop effective treatments for them.
o Scientists can investigate how humans may have changed over time, and even how ancient
populations may have migrated across the globe.
- DNA strands are polymers made up of lots of repeating units called nucleotides. Each nucleotide
consists of one sugar molecule, one phosphate molecule and one base.
- The sugar and phosphate molecules in the nucleotides form a backbone to DNA strands. The sugar and
phosphate molecules alternate. One of four different bases – A, T, C and G joins to each sugar. Each
base links to a base on the opposite strand in the helix. (A with T, C with G).
- It’s the order of bases in a gene that decides the order of amino acids in a protein. Each amino acid is
coded for by a sequence of 3 bases in the gene.
- The amino acids are joined together to make various proteins.
- There are parts of DNA that don’t code for proteins. Some of these non-coding parts switch genes on
and off, so they control whether or not a gene is expressed (used to make a protein).
Protein Synthesis:
- Proteins are made in the cell cytoplasm on tiny structure called ribosomes.
2
