7.1 inherited change

Question 1

what is the genotype?

Answer 1

• the genotype is the genetic constitution of an organism.
• it describes all the alleles that an organism contains.

Question 2

what is the phenotype?

Answer 2

• the phenotype is the observable or biochemical characteristics of an organism.
• it is the result of the interaction between the expression of the genotype and the environment.

Question 3

what is a gene?

Answer 3

a section of DNA (sequence of nucleotides) that codes for a particular polypeptide.

Question 4

what is an allele?

Answer 4

one of the different forms of a gene.

Question 5

explain what it means when alleles are referred to as ‘codominant’.

Answer 5

• alleles are referred to as ‘codominant’ when two alleles both contribute to an organism’s phenotype.
• this means that both alleles are equally dominant.

Question 6

what is monohybrid inheritance?

Answer 6

the inheritance of a single gene.

Question 7

state the law of segregation.

Answer 7

• in diploid organisms, characteristics are determined by alleles that occur in pairs.
• only one of each pair of alleles can be present in a single gamete.

Question 8

what is dihybrid inheritance?

Answer 8

the inheritance of two characteristics, controlled by two different genes, located on two different chromosomes.

Question 9

state the law of independent assortment.

Answer 9

each member of a pair of alleles may combine randomly with either of another pair.

Question 10

explain why Mendel choose pea plants to experiment on.

Answer 10

Mendel chose pea plants to experiment on because they were easy to grow and possessed many contrasting features that could easily be observed.

Question 11

explain the production of an enzyme for an organism that is homozygous for the first allele.

Answer 11

in organisms that are homozygous for the first allele, both alleles code for the enzyme that expresses the dominant characteristic.

Question 12

explain the production of an enzyme for an organism that is homozygous for the other allele.

Answer 12

in organisms that are homozygous for the second allele, no enzyme is produced.

Question 13

explain the production of an enzyme for an organism that is heterozygous.

Answer 13

in a heterozygous organism, both alleles code for an enzyme, so a combination of the phenotype for both alleles is expressed.

Question 14

give the script that is used when writing for codominance.

Answer 14

superscript.

Question 15

any gene that is carried on either the X or Y chromosome is described as what?

Answer 15

sex linked.

Question 16

explain why characteristics that are controlled by recessive alleles on the non-homologous portion of the X chromosome appear more frequently in males.

Answer 16

because in males, there is no homologous portion on the Y chromosome that might contain the dominant allele, in the presence of which the recessive allele does not express itself.

Question 17

an X-linked genetic disorder is caused by what?

Answer 17

a defective gene on the X chromosome.

Question 18

give an example of an X-linked disorder in humans.

Answer 18

haemophilia.

Question 19

give an example of one of a number of causes of haemophilia.

Answer 19

one of a number of causes of haemophilia is a recessive allele with an altered sequence of DNA nucleotide bases that codes for a faulty protein which does not function.

Question 20

other than sex chromosomes, which are sex-linked, what are the remaining 22 chromosomes called?

Answer 20

autosomes.

Question 21

describe ‘autosomal linkage’.

Answer 21

autosomal linkage refers to when two or more genes are carried on the same chromosome.

Question 22

if two genes are heterozygous linked, how many combinations of alleles will be found in the gametes? how is this different from heterozygous unlinked?

Answer 22

heterozygous linked - two possible combinations of alleles in the gametes

heterozygous unlinked - four possible combinations of alleles in the gametes

Question 23

when does epistasis arise?

Answer 23

epistasis arises when the allele of one gene affects or masks the expression of another in the phenotype.

Question 24

give an example of another form of epistasis, other than gene masking.

Answer 24

• another form of epistasis is where genes act in sequence by determining the enzymes in a pathway.
• dominant alleles of each gene code for a functional enzyme, while recessive alleles code for a non-functional enzyme.

Question 25

the chi-squared test is used to test what?

Answer 25

the null hypothesis - whether any deviation between the observed and expected numbers is significant or not.

Question 26

what is a null hypothesis?

Answer 26

a hypothesis that states that there will be no significant difference in the outcome of an experiment.

Question 27

devise an appropriate null hypothesis.

Answer 27

there will be no significant difference between the observed and expected results.

Question 28

give the formula for chi-squared.

Answer 28

chi squared = sum of [observed numbers (O) - expected numbers (E)]² / expected numbers (E)

Question 29

give the conditions that must be met in order to test chi-squared.

Answer 29

• the sample size must be relatively large (over 20)
• the data obtained must fall into discrete categories.
• only raw counts can be used.

Question 30

define the term ‘number of degrees of freedom’.

Answer 30

the number of classes minus one.

Question 31

give the critical value in the chi-squared test.

Answer 31

0.05 (5%)

Question 32

if the probability that the deviation is due to chance is equal to or greater than 0.05, the deviation is said to be what? can the null hypothesis be accepted?

Answer 32

the deviation is said to be not significant, and the null hypothesis would be accepted.

Question 33

if the probability that the deviation is due to chance is less than 0.05, the deviation is said to be what? can the null hypothesis be accepted?

Answer 33

the deviation is said to be significant. the null hypothesis must be rejected, as factors other than chance may be affecting the results.