Topic 8: Genetics Flashcards
What are the sources of variation?
Meiosis, mutations and random fertilisation
How does meiosis cause variation?
Random assortment and crossing over
What is the change in chromosome number during meiosis?
Diploid to haploid
What is random assortment?
When the paternal and maternal chromosomes are sorted into gametes randomly so there are many new combinations of alleles
Explain crossing over
- Prophase 1
- Chromosomes line up into a tetrad
- Chromatids get so close they cross over to form a chiasma
- Chiasma breaks and sections of the chromosomes get switched
What is a tetrad?
A pair of chromosomes
What is a chiasma?
The structure formed when chromosomes cross over
What is a mutation?
A permanent change in the DNA
What are the three main types of mutations?
Point mutations, chromosomal mutations and chromosome mutations
What are the types of point mutations?
Substitution, deletion and insertion
What is a point mutation?
When one base or a small section of the DNA is miscopied
What is a substitution mutation?
When a base is swapped for another
What is an insertion mutation?
When a base is inserted
What is a deletion mutation?
When a base is deleted
What is a chromosomal mutation?
When the genes on a chromosome are moved
What is a chromosome mutation?
When a chromosome is either added or removed
Why does fertilisation introduce variation?
All gametes have a different combination of alleles
Which gametes fuse together is totally random
Define phenotype
Physical and chemical characteristics that make up the appearance of an organism
Define genotype
Genetic information
Define gene
Different segments of DNA coding for a particular protein
Define homologous
When a pair of autosomes have the same genes
Define alleles
Different variations of a gene
Define locus
The position of a gene on a chromosome
Define homozygous
When two alleles for a characteristic are the same
Define heterozygous
When two alleles for a characteristic are different
Define dominance
When a phenotype is expressed regardless of whether the alleles are homozygous or heterozygous
Define recessive
When a phenotype is only expressed if the alleles are homozygous
Define polygenic
Traits that are affected by multiple interacting genes
