alleles, genes and phenotypes

Question 1

wild type

Answer 1

an allele that is common and thought of as the default phenotype
other alleles known as mutant alleles

Question 2

polymorphic

Answer 2

a gene with multiple alleles

Question 3

codominance

Answer 3

2 alleles that produce different phenotypes are both expressed

can interact and are both expressed

eg blood types

Question 4

gene interactions

Answer 4

phenotypes can be determined by the genotype at more than one gene

eg epistasis

Question 5

epistasis

Answer 5

when the phenotypic expression of one gene is influenced by products of the other genes

Question 6

environmental effects

Answer 6

DNA doesn’t have the only impact
- light, temperature, nutrition etc

Question 7

penetrance

Answer 7

proportion of individuals with a genotype that develop the expected genotype

Question 8

expressivity

Answer 8

the degree to which a phenotype is expressed in an individual

Question 9

complex phenotypes

Answer 9

phenotype vary continuously over a range

opposite of discrete phenotypes studied by Mendel

Question 10

qualitative traits

Answer 10

have discrete qualities
often controlled by alleles at a single locus

Question 11

quantitative traits

Answer 11

show continuous variation

can be influenced by gene at many loci and the environment
results of many genes and the environment

Question 12

genetic linkage

Answer 12

violation of the law of independent assortment
monohybrid crosses don’t result in 9:3:3:1 ratio

alleles of genes on same chromosome can be inherited together
due to physical linkage as closely located
unlikely recombination will break them up

Question 13

why is absolute linkage rare?

Answer 13

genes may recombine during prophase 1 of meiosis by crossing over
chromosomes exchange corresponding segments
exchange can occur at any point along length of chromosome
mostly broken up

Question 14

recombinant frequencies

Answer 14

how often recombination occurs
- used to infer location of genes on a chromosome
- used to make genetic maps

Question 15

recombinant offspring frequencies

Answer 15

number of recombinant offspring divided by total number of offspring

recombinant frequencies greater for genes that are further apart because an exchange event is more likely to occur between genes that are far apart

Question 16

sex linkage

Answer 16

females have 2 X chromosomes
males have 1 X 1 Y

male mammals produce 2 kinds of gametes with half X and half Y
sex of offspring depends on which gamete fertilises the egg

some trait other than sex are carried o the sex chromosomes and inherited

Question 17

homogametic sex

Answer 17

will have 2 copies of the gene (2 alleles)
eg XX

Question 18

heterogametic sex

Answer 18

will have 1 copy
eg XY

Question 19

hemizygous

Answer 19

a gene that is present in a single copy in an otherwise diploid individual