Topic three: genetics (biology)
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27 Terms
What is the definition of a gene?
DNA sequence coding for a trait
What is the definition of an allele?
An alternative form of a gene
What is a genotype?
The genetic make up
What is a phenotype?
An observable trait
What does heterozygous mean?
Different alleles
What is a dominant allele?
The phenotype is Expressed when present
What is a recessive allele?
When the phenotype is only expressed when the alleles are homozygous in the genotype
What is the law of segregation?
Where all separate during gamete formation
What is a punnett square used for?
To predict genotype probability
What is the Dihybrid cross ratio?
9:3:3:1
What is independent assortment?
Wear genes assort independently
What is a test cross?
Across with a homozygous recessive
What is meant by codominance
Where both alleles are expressed because neither is more dominant than the other
What is incomplete dominance?
We again neither are more dominant than the other but this time it results in a blended phenotype
What are an example of multiple alleles?
Having an ABO blood group
What is sex linked inheritance?
It means that the affected genes are on the X or Y chromosome so the sex chromosomes
Why are males affected more with an X linked trait?
Because males only have one X chromosome whereas females have two so female males need to affected to be affected where is males and they need one
What is meiosis?
Cell division producing for haploid genetically different cells
What is the purpose of meiosis?
To produce gametes
What is the definition of diploid?
Having two sets of chromosomes (2n)
What is the definition of haploid?
Having one set of chromosomes (n)
What are homologous chromosomes?
Chromosomes with the same genes
When does crossing over occur?
Prophase one
What is the definition of crossing over?
The exchange of DNA between homologous chromosomes
What is another term for crossing over?
Recombination or homologous recombination, with the visible evidence of this exchange being called a chiasma (plural chiasmata)
When does independent assortment occur?
Metaphase one
Why does meiosis produce variation?
Due to crossing over or homologous recombination
Independent assortment
And random fertilisation
