B6 - Inheritance, variation and Evolution Flashcards
Describe the differences between sexual and asexual reproduction
Sexual reproduction - The fusion of male and female gametes (genetic information from both male and female parent)
Asexual reproduction - Only 1 parent (offspring are genetically identical/ clones)
Describe how meiosis halves the number of chromosomes in gametes
- The chromosomes are copied
- The cell divides into 2
- Both of these cells divide one more time, forming the gametes (single chromosomes)
Describe how fertilisation restores the full number of chromosomes
The gametes join together to form pairs of chromosomes through sexual reproduction
What are the advantages of sexual reproduction?
Sexual reproduction produces variation in the offspring, meaning some of the offspring may survive if the environment changes.
It gives a species a greater chance of survival if conditions become challenging.
Selective breeding produces a high yield of good-quality offspring.
What are the advantages of asexual reproduction?
Only one parent is needed, meaning it is more efficient in both time and energy as there is no need to find a mate.
It is extremely useful when conditions are favourable as an organism can produce many genetically identical offspring rapidly
What are the disadvantages of asexual reproduction?
It is very risky - because all the offspring are genetically identical, there is a risk they could all die if conditions become unfavourable
What are the disadvantages of sexual reproduction?
It takes time and energy to find a mate.
It is not possible for an isolated individual to reproduce
Compare meiosis and mitosis
Meiosis includes two nuclear divisions which produce non-identical daughter cells. Each daughter cell contains one set of chromosomes.
Mitosis includes one nuclear division that produces two identical daughter cells. Each daughter cell contains two full sets of chromosomes.
What are the names of the male and female gametes in:
1) Plants
2) Animals
1) Pollen cells and egg cells
2) Sperm cells and egg cells
What is asexual reproduction?
When there is only one parent and no fusion of gametes. Only mitosis is involved, so there is no mixing of genetic information. The offspring are genetically identical (clones).
Describe how three different organisms reproduce both sexually and asexually:
1) Malarial Parasites
2) Fungi
3) Plants
1) Malarial parasites reproduce asexually in the human host and sexually in the mosquito.
2) Fungi reproduce asexually by spores, but also reproduce sexually to give variation.
3) Plants reproduce sexually, but some also reproduce asexually. Strawberry plants reproduce asexually via runners; daffodils reproduce asexually via bulb division.
Describe the structure of DNA
DNA is a polymer made up of two strands of nucleotides that are twisted to form a double helix.
Describe how protein synthesis occurs
A template is made of the DNA.
The template moves from the nucleus to the cytoplasm of the cell where it attaches to a ribosome.
A carrier molecule attaches to every three bases of the template.
The carrier molecule is attached to an amino acid.
The amino acids are joined together to form a chain.
The chain folds into the final shape of the protein.
What effect might a mutation in a non-coding region of DNA have?
It might change the expression of a gene
Define Genome
The entire genetic material of an organism
Define Gamete
The sex cells which contain one set of genetic information
Define chromosome
Found in the nucleus, they are made from long DNA molecules and passed from parent to offspring
Define Gene
A section of DNA that codes for a particular sequence of amino acids which makes a specific protein
Define allele
A different form or variant of a gene
Define dominant
Controls the characteristic, even if it is only present on one chromosome
Define recessive
Only controls the physical characteristic if it is present on both chromosomes
Define Homozygous
Two identical alleles for a characteristic
Define heterozygous
Different alleles for a characteristic
Define genotype
The alleles present in an individual for a particular characteristic
Define phenotype
The physical appearance of an individual for a particular characteristic
Explain why it’s important for us to study the human genome
It helps us to search for genes that are linked to different types of diseases.
Understanding inherited disorders gives us more chance of repairing the genes or producing successful medicines.
It also helps us to trace the migration patterns of humans from the past to develop a greater understanding of human evolution.
What is the evolution script?
(E.g. for Ducks)
There is variation in the population of ducks due to random mutations.
Ducks with webbed feet can compete to swim faster and get more food.
Therefore they are more likely to survive, reproduce and pass on the genes for webbed feet.
What is meant by complementary strands?
The same bases always pair on the opposite strands.
A - T
G - C
A change to a base is a…
Mutation
What happens if mutations code for an altered protein with a different shape?
An enzyme may no longer fit the substrate binding site or a structural protein may lose its strength.
Describe the inherited disorder cystic fibrosis
• A disorder of cell membranes.
• Controlled by a single gene.
• Two alleles - allele for defective cell membranes is recessive
Describe the inherited disorder polydactyly
• Having extra fingers or toes
• Dominant allele
• Cannot be a carrier of the allele - true of any dominant allele
Describe the issues around embryo screening
• Expensive - some think that the money should be spent elsewhere in the health service.
• Some healthy embryos destroyed - unethical.
• Producing offspring with desirable features is seen as unethical.
Human body cells contain (..) of chromosomes
23 pairs
How many pairs control characteristics only & how many pairs carry the genes that determine sex?
• 22 pairs control characteristics only
• 1 pair carries the genes that determine sex
Female sex chromosomes are:
XX
Male sex chromosomes are:
XY
Describe the causes of variation
• the genes they have inherited (genetic causes
• the conditions in which they have developed (environmental causes)
• a combination of genes & the environment
