BY5 Genetics definitions.

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  1. Gene.
    section of DNA that codes for a specific protein or polypeptide.
  2. Locus.
    A specific position of a gene on a chromosome.
  3. Allele.
    One of the different forms of a particular gene, which arises as a result of gene mutation.
  4. Gene point mutation.
    • A change in the nucleotide sequence of a gene. 
    • Therefore a gene mutation may result in a change in the amine acid sequence of a protein.
  5. Phenotype.
    The physical, observable, measurable characteristics of an organism.
  6. Genotype.
    The genetic make-up of an organism.
  7. Homozygous.
    • Genotype where the alleles of a particular gene are identical to each other.
    • eg. GG
  8. Heterozygous.
    • Genotype with contrasting alleles.
    • eg. Gg
  9. Dominant.
    An allele is said to be dominant if it is always expressed in the phenotype of an organism.
  10. Recessive.
    • An allele is said to be recessive if it is only expressed in the phenotype of an organism if the other allele paired is identical.
    • If an organism shows the recessive characteristics in the phenotype then the genotype must be homozygous recessive.
  11. Monohybrid Cross.
    A genetic cross between individuals in which a single gene is being considered.
  12. Dihybrid cross.
    • A genetic cross between individuals in which genes at two different loci are considered.
  13. Multiple Alleles.
    A single gene that has more that two forms.
  14. Codominance.
    Two alleles are said to be codominant if both are expressed fully and equally in the phenotype of the heterozygote.
  15. Pure breeding.
    Organisms which, when crossed, produce offspring identical to their parents.
  16. Test cross/backcross
    A cross performed to determine an unknown genotype.
  17. Autosomal Linkage.
    Refers to two or more genes found on the same chromosome.
  18. Sex linkage.
    • A characteristic is said to be sex linked if it is controlled by a gene carried on one of the sex chromosomes. 
    • Y chromosome is very small and carries few genes, therefore sex linked genes are more likely to be found on the X chromosome. 
  19. Polygenic inheritance.
    Where a number of genes are responsible for controlling a characteristic.
  20. Mendel's First Law.
    The characteristics of an organism are determined by factors ( alleles) which occur in pairs.
  21. Mendel's Second Law.
    • Either one of a pair of contrasted characters may combine with either of another pair.
    • Each member of an allele pair may combine randomly with either of another pair.
  22. Overproduction
    All organisms have the reproductive potential to greatly increase their populations but rarely do so due to limiting factors. 
  23. Intraspecific competition
    • Competition between individuals of the same species. tra - intranet
    • The basis of origin on species by natural selection.
  24. Population
    Individuals of the same species occupying a particular area.
  25. Genotype frequency.
    The number of times a particular genotype occurs in a population.
  26. Allele Frequency
    The number of times a particular allele occurs in a population.
  27. Selection pressure
    • Environmental pressure that results in the survival of the best adapted organisms in a population.
    • Thus produces changes in the allele frequency in the gene pool.
  28. Genetic drift.
    Random variations in allele frequencies which occur in populations by chance.
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BY5 Genetics definitions.
2014-05-05 15:23:59

Wjec BY4
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