9 - Inheritance (C2) Flashcards
What is the definition of a gene?
A sequence of DNA that codes for a polypeptide and which occupies a specific locus on a chromosome
What is the definition of an allele?
A variant nucleotide sequence for a particular gene at a given locus, which codes for an altered phenotype
What does homozygous mean?
The alleles of a particular gene are the same
What does heterozygous mean?
The alleles of a particular gene are different
What is the genotype of an individual?
The alleles that they contain
What is the phenotype of an individual?
A description of their appearance, including characteristics that can’t be seen, e.g. their blood group
What is a dominant allele?
An allele that has the same effect on the phenotype of a heterozygote as a homozygote
What is a recessive allele?
An allele is only expressed when in a homozygous pair and when no dominant allele is present
What is co-dominance?
When both alleles contribute to the phenotype
What is monohybrid inheritance?
The inheritance of a single gene
Why are peas useful to be used in inheritance experiments?
- They’re easy to grow
- Their flowers can self-fertilise and cross-fertilise
- They make flowers and fruit in the same year
- They make a large number of seeds from each cross
Why did Mendel chose to study pairs of contrasting characteristics e.g. tall or dwarf plants?
- They’re controlled by single genes
- They’re controlled by genes on different chromosomes
- Easy to tell apart
What is continuous variation?
Variation with a range of values that’s controlled by a number of genes e.g. height
What is incomplete dominance?
When neither allele is dominant so the offspring phenotype is intermediate between that of the 2 homozygotes e.g. red flower + white flower -> pink flower
What are linked genes?
Genes that are on the same chromosome and therefore are not separated at meiosis
What increases the likelihood of crossing over of genes?
The further apart 2 genes are on a chromosome, the more opportunity there is for crossover to occur between them
What number is the degrees of freedom?
1 less than the number of classes of data
Why are the sex chromosomes called heterosomes?
Because they’re different sizes