unit 3 Flashcards
(21 cards)
what is a test cross
testing a suspected heterozygous by crossing it with a known homozygous recessive
what is a dominant allele
an allele with a phenotype that is expressed even when present with an allele that is recessive to it
what is an allele
1 or 2 or more alt. nucleotide sequences at a single gene locus: alleles are variant forms of genes
what is a diploid
a eukaryotic cell or organism containing 2 complete sets of chromosomes (2 copies of each homologous chromosomes)
what is a gene
a length of DNA that codes for a particular polypeptide/protein
what is a haploid?
a eukaryotic cell or organism containing only one complete set of chromosomes (only 1 of each homologous chromosomes)
what is a codominant allele
alleles that are both expressed if they are present together in a heterozygous person
what is a heterozygous
a genotype in which the 2 alleles of a gene are different
what is a recessive allele
an allele with a phenotype that is not expressed when an allele that is dominant to it is present
what is a homozygous
a genotype in which the two alleles of a gene are the same
what is a phenotype
the appearance of the organism: the way in whih the genotype of the organism is expressed
what is a genotype
the alleles that an organism carries
what is a locus
the position on the chromosomes where a gene occurs; alleles of the same gene occupy the same locus
what is codominance?
alleles that are both expressed if they are present together in a heterozygous organism
what is incomplete dominance?
the phenotype of F1 hybrid is somewhere between the phenotypes of the 2 parental varieties
multiple alleles
3 or more alleles (alt. forms of a gene) that can occupy the same locus. in each indiv. only 2 of these alleles exist, but they are inherited as if they were alternative alleles of a pair
sex linkage
any gene present on the sex chromosomes is likely to be inherited with the sex of the individual
what is a carrier?
a heterozygous individual with 1 dominant allele and 1 recessive allele of a gene, the recessive allele is not expressed thus will not have an effort on the phenotype as it is masked by the presence of the dominant allele. the unpaired alleles of the x-chromosomes in a male (XY) are all expressed. the alleles on the short Y chromosome are mostly concerned with male structures and male functions
what can variation be caused by? (3 points)
- some differences may be controlled by genes (eg. blood type)
- other differences may be due to environmental factors
- other differences may be due to both genetics & environment (eg. body height and weight)
what are the 3 characteristics of continuous variation?
- no clear-cut differences with infinite varieties
- controlled by a number of genes (polygenes)
- affected by environmental conditions/factors
what are the 3 characteristics of discontinuous variation?
- clear-cut differences with no intermediate form
- controlled by a single pair of alleles of a gene
- unaffected by environmental conditions/factors
