unit 3

Question 1

what is a test cross

Answer 1

testing a suspected heterozygous by crossing it with a known homozygous recessive

Question 2

what is a dominant allele

Answer 2

an allele with a phenotype that is expressed even when present with an allele that is recessive to it

Question 3

what is an allele

Answer 3

1 or 2 or more alt. nucleotide sequences at a single gene locus: alleles are variant forms of genes

Question 4

what is a diploid

Answer 4

a eukaryotic cell or organism containing 2 complete sets of chromosomes (2 copies of each homologous chromosomes)

Question 5

what is a gene

Answer 5

a length of DNA that codes for a particular polypeptide/protein

Question 6

what is a haploid?

Answer 6

a eukaryotic cell or organism containing only one complete set of chromosomes (only 1 of each homologous chromosomes)

Question 7

what is a codominant allele

Answer 7

alleles that are both expressed if they are present together in a heterozygous person

Question 8

what is a heterozygous

Answer 8

a genotype in which the 2 alleles of a gene are different

Question 9

what is a recessive allele

Answer 9

an allele with a phenotype that is not expressed when an allele that is dominant to it is present

Question 10

what is a homozygous

Answer 10

a genotype in which the two alleles of a gene are the same

Question 11

what is a phenotype

Answer 11

the appearance of the organism: the way in whih the genotype of the organism is expressed

Question 12

what is a genotype

Answer 12

the alleles that an organism carries

Question 13

what is a locus

Answer 13

the position on the chromosomes where a gene occurs; alleles of the same gene occupy the same locus

Question 14

what is codominance?

Answer 14

alleles that are both expressed if they are present together in a heterozygous organism

Question 15

what is incomplete dominance?

Answer 15

the phenotype of F1 hybrid is somewhere between the phenotypes of the 2 parental varieties

Question 16

multiple alleles

Answer 16

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

Question 17

sex linkage

Answer 17

any gene present on the sex chromosomes is likely to be inherited with the sex of the individual

Question 18

what is a carrier?

Answer 18

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

Question 19

what can variation be caused by? (3 points)

Answer 19

1. some differences may be controlled by genes (eg. blood type)
2. other differences may be due to environmental factors
3. other differences may be due to both genetics & environment (eg. body height and weight)

Question 19

what are the 3 characteristics of continuous variation?

Answer 19

1. no clear-cut differences with infinite varieties
2. controlled by a number of genes (polygenes)
3. affected by environmental conditions/factors

Question 19

what are the 3 characteristics of discontinuous variation?

Answer 19

1. clear-cut differences with no intermediate form
2. controlled by a single pair of alleles of a gene
3. unaffected by environmental conditions/factors