20 - Patterns of Inheritance and Variation Flashcards
How is closeness of two linked genes on a chromosome linked to the number of recombinant offspring?
More closely linked genes means less separation and so less recombinant offspring
What is a phenotype?
Physical characteristics of an organism
What is a genotype?
Genetic makeup of an organism
What 2 things affect an organism’s phenotype?
Genotype and environment
What is it called when a characteristic is codes for by multiple genes?
Polygenic
What type of characteristics tend to be polygenic?
Ones which vary within a range, such as height
What is continuous variation?
A characteristic that can take any value within a range
What is discontinuous variation?
A characteristic that can only result in certain values
What does it mean if something is monogenic?
Controlled by only 1 gene
What type of characteristics tend to be monogenic?
Ones which exhibit discontinuous variation
What are the 3 things which affect genotype?
- Sexual reproduction 2. Gene mutations 3. Chromosome mutations
What 2 characteristics do all mutations which take place during gamete formation have?
- Persistent (passed through many generations) 2. Random (so not directed by need)
When do chromosome mutations occur?
During meiosis
What happens in a deletion chromosome mutation?
Part of the chromosome, containing genes and regulatory sequences, is lost
What happens in an inversion chromosome mutation?
Sections of chromosome break off, turn around 180 degrees and rejoin
Why might genes not be expressed after an inversion chromosome mutation despite still being present?
They may be too far away from their regulatory nucleotide sequence
What happens in a translocation chromosome mutation?
A piece of chromosome breaks off and reattaches to another chromosome
What happens in a duplication chromosome mutation?
Part of the chromosome is duplicated, which can lead to harmful overexpression of certain genes
What type of mutation causes Downs syndrome?
Non-disjunction chromosome mutation
What happens in a non-disjunction chromosome mutation?
One pair of chromatids fails to separate, leaving one gamete with an extra chromosome
What are 3 ways in which sexual reproduction can cause genetic variation?
- Allele shuffling during crossing over 2. Independent assortment 3. Random fertilisation, where any male gamete can fertilise any female gamete
What is etiolation?
Where plants grow long and spindly due to a lack of light and they grow fast so they can reach the light
What is chlorosis?
The yellowing of leaves due to a lack of Magnesium ions (Mg2+) which means chlorophyll cannot be made
What are 3 examples of environmental factors which can affect phenotype?
- Diet in humans 2. Etiolation 3. Chlorosis