B13 Reproduction Flashcards
What creates genetic variation in a species?
Spontaneous mutations
Sexual reproduction
What is a mutation?
A random change to the base sequence in DNA which results in genetic variants. They occur continuously.
What are the 3 types of mutation?
- Insertions:
A new base is randomly inserted into the DNA sequence
An insertion mutation changes the amino acid that would have been coded for by
the group of three bases in which the mutation occurs
Remember – every group of three bases in a DNA sequence codes for an amino
acid
An insertion mutation also has a knock-on effect by changing the groups of three
bases further on in the DNA sequence - Deletions
A base is randomly deleted from the DNA sequence
Like an insertion mutation, a deletion mutation changes the amino acid that
would have been coded for by the group of three bases in which the mutation occurs.
Like an insertion mutation, a deletion mutation also has a knock-on effect by
changing the groups of three bases further on in the DNA sequence - Substitutions
A base in the DNA sequence is randomly swapped for a different base
Unlike an insertion or deletion mutation, a substitution mutation will only change
the amino acid for the group of three bases in which the mutation occurs; it will
not have a knock-on effect
How may a gene mutation affect an organism’s phenotype?
- Neutral mutation does not change the sequence of amino acids. Protein structure and function same. No effect on phenotype
- Mutation may cause a minor change in an organism’s phenotype e.g. change in eye colour.
- Mutation may completely change the sequence of amino acids. This may result in a non-functional protein. Severe changes to phenotype.
Do all mutations alter proteins?
Most do not alter the protein or alter it only slightly so the function is not affected. A few mutations code for a protein with a different shape, which affects the function. This might cause an advantage or a disadvantage.
What happens when mutations take place in non coding DNA?
These mutations do not directly affect the phenotype. But the can affect which genes are switched on/ off. By changing the genes that are expressed there might be a big impact on the phenotype.
What is meant by gene expression?
Gene expression is when a gene codes for a protein that is synthetized in a cell
What is the role of non coding parts of the DNA?
They switch genes on and off so variations in these parts of DNA may vary how genes are expressed.
If a mutation occurs in a section of non-coding DNA that controls gene expression, the expression of these genes may be altered or in some cases, the mutation may cause them not to be expressed at all
How can humans synthetize so many proteins with so few genes?
Because non coding parts of DNA can switch genes on and off
What is sexual reproduction?
- Involves the production of gametes (sex cells) by meiosis.
- A gamete from each parent fuses to form a zygote.
- Genetic information from each gamete is mixed so the resulting zygote is unique.
- Offspring inherit some characteristics from both parents.
What are gametes?
Sex cells (sperm cells and egg cells in animals, pollen and egg cells in flowering plants).
What is meiosis?
- Form of cell division involved in the formation of
gametes (non-identical haploid cells) in reproductive organs. - Chromosome number is halved.
- Involves two divisions.
Describe the process of meiosis?
- Each chromosome is duplicated, forming X-shaped chromosomes
- First division: the chromosome pairs line up along the centre of the cell and are then pulled apart so that each new cell only has one copy of each chromosome
- Second division: the chromosomes line up along the centre of the cell and the arms of the chromosomes are pulled apart
- A total of four haploid daughter cells will be produced
What does it mean that gametes are haploid?
We describe gametes as being haploid – having half the normal number of chromosomes
Why is meiosis important?
- Produces gametes eg. sperm cells and egg cells in animals, pollen grains and ovum cells in plants
- Increases genetic variation of offspring
- Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others
What happens during fertilisation?
- Gametes join at fertilisation to restore the normal number of chromosomes
- When the male and female gametes fuse, they become a zygote (fertilised egg cell)
- This contains the full number of chromosomes, half of which came from the male gamete and half from the female gamete
- The zygote divides by mitosis to form two new cells, which then continue to divide and after a few days form an embryo
- Cell division continues and eventually many of the new cells produced become specialised (the cells differentiate) to perform particular functions and form all the body tissues of the offspring
- The process of cells becoming specialised is known as cell differentiation
What is asexual reproduction?
- Asexual reproduction does not involve sex cells or fertilisation
- Only one parent is required so there is no fusion of gametes and no mixing of genetic information
- As a result, the offspring are genetically identical to the parent and to each other (clones)
- Asexual reproduction is defined as a process resulting in genetically identical offspring from one parent
- Only mitosis is involved in asexual reproduction
What are the pros and cons of sexual reproduction?
+ Increases genetic variation
The species can adapt to new environments thanks to mutations. This gives them a survival advantage
Disease is less likely to affect a population due to mutations
An additional advantage of sexual reproduction is our ability to use it and control it for our own needs:
- Natural selection can be speeded up by humans in selective breeding to increase food production
We have controlled sexual reproduction in cows and selectively bred them to produce offspring that produce more milk and more meat than they would have under natural conditions
- Time and energy to find a partner
Hard for isolated member of a species to reproduce
Advantages and disadvantages of asexual reproduction
+
- Population can increase rapidly when conditions are right
- more time and energy efficient
- much faster
Cons
- offspring identical to parents
- population is vulnerable to change in conditions and might be suited for only one habitat
- disease is likely to affect the whole population
What are examples of organisms that reproduce both sexually and asexually?
Malarial parasites
- Malaria is caused by parasites that are carried by mosquitoes
- The parasites are transferred to a human when the mosquito feeds on the human’s blood
- These malarial parasites reproduce asexually in the human host, but sexually in the mosquito
Fungi
- Many fungi reproduce both asexually and sexually
- These species of fungi release spores, which develop into new fungi
- These spores can be produced via asexual or sexual reproduction
- Spores that are produced via sexual reproduction show variation (they are genetically different from each other)
Plants
- Many plants produce seeds via sexual reproduction but are also able to reproduce asexually
- They reproduce asexually in different ways:
Some plants (eg. strawberry plants) produce ‘runners’ (stems that grow horizontally away from the parent plant, at the end of which new identical offspring plants form)
Some plants (eg. daffodils) reproduce via bulb division (new bulbs form from the main bulb underground and then grow into new identical offspring plants)
What is meant by genome?
The entire set of the genetic material of an organism is known as its genome
What is The Human Genome Project
The Human Genome Project (completed in 2003) was the name of the international, collaborative research effort to determine the DNA sequence of the entire human genome and record every gene in human beings
This was a very important breakthrough for several reasons:
From a medical perspective, as it has already and will continue to improve our understanding of the genes linked with different types of disease and inherited genetic disorders, as well as the help us in finding treatments
The human genome has also made it possible to study human migration patterns from the past, as different populations of humans living in different parts of the world have developed very small differences in their genomes
What is DNA
-The genetic material in the nucleus of a cell is composed of a chemical called DNA. DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for growth and development of all organisms.
DNA is a polymer made up of two strands forming a double helix
DNA is contained in structures called chromosomes
Chromosomes are located in the nucleus of cells
What are genes?
A gene is a short length of DNA found on a chromosome. Each gene codes for a particular sequence of amino acids. These sequences of amino acids form different types of proteins.
There are many different types of proteins but some example of these could be:
structural proteins such as collagen found in skin cells
enzymes
hormones
Genes control our characteristics as they code for proteins that play important roles in what our cells do
