Define...
Homozygous
Two alleles the same eg. aa
How many letters should be in each of the outside boxes of as punnett square?
Only one
How many chromosomes do you get from each parent?
23
What is a mutation?
A permanent change in the DNA
What is a population?
A group of individuals of the same species living in one area.
Allele
Alternative form of a gene e.g. blue vs brown eyes
A white rat, bb, breeds with a black rat, BB. How many of the offspring will be black?
All of them
What is the name of the code of inheritance?
DNA
Is height in humans determined by genetics, environment or both?
Both - genetic potential for height can be altered by environmental factors e.g. malnutrition, growth hormone exposure
How does migration affect genetic variation?
It increases variation by mixing alleles between populations?
Gene
A sequence of DNA that codes for a protein/trait
What is the expected phenotype ratio in the offspring of two heterozygous individuals?
3:1
How can a mutation pass to the next generation?
Only through gametes
What is the advantage of having variation in a population?
If there is a change in environment, some may survive to pass on successful genes to future generations.
What might cause a population bottleneck?
A natural disaster eg. volcano, earthquake, asteroid.
Genetic variation
A Punnett square predicts that half of parents' offspring will be male and half female. How can a family have five female and no male offspring?
Every fertilisation is random 50:50 chance. Previous offspring have no influence on likelihood of later siblings being male or female.
Which two processes in meiosis reshuffle the parents genes but don't actually create any new alleles?
Independent assortment and crossing over
Birds with longer beaks were more likely to survive a drought than short beaked birds. What is the likely outcome for this population if drought conditions continue?
Long beaked bird will be more successful in surviving and breeding and will pass on long beak alleles to their offspring. Short beaked birds will be less likely to survive and reproduce, passing on no genes. The population will show an increasing frequency of long beaks each generation.
Why would the founder effect reduce genetic variation?
When a small number of individuals colonise a new area, this small population has a non-representative sample of the original populations gene pool.
Genotype
The alleles present in an individual e.g. Aa
Two brown bunnies have two brown and two white offspring. Explain why this proves white colouring is recessive.
Parents must be heterozygous - their dominant allele gives them a brown coat but they each carry a hidden white allele. Their white offspring got a recessive allele from each parent.
It can't be dominant because that would make parents homozygous recessive, and they wouldn't have any white alleles to pass to their offspring.
Using the terms DNA, mutation, allele, phenotype, explain how a mutation in a gene can cause albinism (can't make melanin to colour skin and hair).
A mutation in the DNA sequence that codes for the gene to make melanin could change the protein created. This altered sequence would be a different allele for the melanin gene. The phenotype produced would be white hair and skin because the melanin protein is different because of the different DNA sequence.
How does sexual reproduction result in variation in beak length of a bird species? Include the processes of gamete formation and fertilisation.
Sexual reproduction is two parents creating a unique offspring from two gametes.
Meiosis is gamete formation. Independent assortment (random lining up on equator in homologous pairs) and crossing over (swapping DNA between homologous pairs) shuffles the parental DNA to make unique gametes with half the number of chromosomes.
It is random which sperm meets which egg in fertilisation, combining DNA from both parents. Offspring therefore show variation. Beak length will depend on which alleles for beak length were inherited from each parent.
What is inbreeding depression and in which populations is it more likely?
In very small populations, there is a higher risk of inbreeding, increasing the chance of harmful recessive alleles pairing and expressing traits that reduce fitness.