B5.1 Flashcards
(48 cards)
What is a gamete?
An organism’s reproductive cell (egg in females, sperm in males), which has half the number of chromosomes (23).
What is a chromosome?
A structure found in the nucleus made up of a long strand of DNA.
What is a gene?
A short section of DNA that codes for a protein and contributes to a characteristic.
How are characteristics controlled by genes?
Some characteristics are controlled by a single gene (e.g. fur colour in mice,
but most characteristics result from many genes interacting
What is an allele (or variant)?
Different forms of the same gene. Humans inherit one allele from each parent, so they have two alleles for each gene.
What is a dominant allele?
Only one copy is needed for it to be expressed and for the phenotype to be observed.
What is a recessive allele?
Two copies are needed for it to be expressed and the phenotype to be observed.
What does homozygous mean?
When both inherited alleles are the same (e.g. two dominant or two recessive alleles).
What does heterozygous mean?
When one allele is dominant and the other is recessive.
What is genotype?
The combination of alleles an individual has, e.g. Aa.
What is phenotype?
The physical characteristics observed in the individual, e.g. eye colour.
What is the genome?
All the genetic information of an organism.
How do the genome and environment affect traits?
They influence how genetic traits are presented — this results in phenotypes.
What is continuous variation?
Variation such as height — controlled by multiple genes and affected by the environment, a range of categories
What is discontinuous variation?
Variation such as eye colour — distinct categories, often controlled by single genes
How has studying the genome helped science?
It has improved understanding of genetic diseases, treatment of inherited disorders, and tracing human migration.
What causes genetic variance?
All variants (alleles) are caused by mutations.
Do all mutations affect phenotype?
No — most mutations occur in non-coding DNA and don’t affect proteins.
When can a mutation affect phenotype?
If it’s in a coding region, it may change protein structure and activity, potentially changing phenotype.
What happens if a mutation is in coding DNA?
It can alter protein structure, e.g. changing enzyme active sites so substrates can’t fit.
What happens if a mutation is in non-coding DNA?
It may affect gene expression by stopping transcription of mRNA.
What is an advantage of sexual reproduction?
Produces variation in offspring.
Why is variation helpful?
Increases chance of survival if environment changes — gives a survival advantage.
How does variation help species survive?
It reduces the chance of the entire species becoming extinct.
