genetics

Question 1

what is the genotype

Answer 1

the genetic constitution of an organism

Question 2

what is the phenotype

Answer 2

the expression of the genotype and its interaction with the environment

Question 3

what are alleles

Answer 3

variants of a particular gene

Question 4

what is a characteristic that has multiple alleles

Answer 4

eye colour e.g. blue, green, brown

Question 5

what is the cause of multiple alleles

Answer 5

mutations in a gene that occur at different positions in the genes

Question 6

what occurs in diploid cells

Answer 6

chromosomes form pairs called homologous chromosomes

Question 7

how can a pair of alleles be homozygous/ heterozygous

Answer 7

alleles at a specific locus can be homologous if they’re the same type of allele
they are heterozygous if the alleles are different

Question 8

how many copies of a particular allele in a genotype

Answer 8

there are 2 copies of a particular allele for the genotype as chromosomes form homologous pairs

one copy is from each parent

Question 9

when is an allele dominant

Answer 9

an allele is dominant if it’s always expressed in the phenotype( of a heterozygous) so only one copy is needed for expression

Question 10

when is an allele recessive

Answer 10

an allele is recessive if it’s not expressed in the phenotype of a heterozygous

so 2 copies have to present for expression

Question 11

what are codominant alleles

Answer 11

both alleles are equally dominant and equally expressed in the phenotype e.g. blood group AB

Question 12

what can monohybrid crosses be used for

Answer 12

they can be used to predict the outcome of crossing two different genotypes

e.g. Parental gentoype CC cc

Gametes: C C c c

Question 13

what is the ratio when you cross heterozygous genotypes together in monohybrid crosses

Answer 13

3: 1

dominant to recessive

Question 14

how can a monohybrid cross be used to identify unknown genotypes

Answer 14

e.gg. an unknown genotype is crossed with a homozygous recessive individual

If all the offspring have a dominant phenotype, the unknown genotype is homozygous dominant as they must have inherited the homozygous allele from the unknown genotype

if half of the offspring have recessive phenotype then the unknown genotype is heterozygous as some individuals have inherited the recessive allele form the unknown genotype

Question 15

what do we use dihybrid crosses for

Answer 15

to work out the inheritance of 2 different genes together

e.g. parental alleles: RRYY rryy R= round r= wrinkles Y = green y = yellow

Gametes: RY RY ry ry

Question 16

what is the ratio of characteristics for dihybrid crosses

Answer 16

9: 3: 3: 1

Question 17

what is an autosome

Answer 17

autosomes are chromosomes that are not sex chromosomes

Question 18

what happens when there are two or more genes located on the same autosome

Answer 18

when there is 2 or more genes located on the same autosome, they are less likely to be separated during crossing over so they are inherited together

this can impact the ratio of phenotypes

e.g. the GB alleles and the gb alleles in the GgBb parent may have been linked. This means the GgBg parent produced mostly GB and gb gametes and makes the GbBg and ggbb genotypes more common in the offspring.
This results in a higher proportion of the offspring would have their parent’s phenotypes, instead of the split even of phenotypes predicted

Question 19

what are do the phenotypes of the offspring in autosomal linkage tend to look like

Answer 19

offspring are more likely to enable parental phenotype as the alleles are less likely to cross over during meiosis

Question 20

when does sex linkage occur

Answer 20

when the gene is only on the X chromosome

therefore, males are more likely to have recessive conditions e.g. hemophilia because they only require one copy of the sex-linked recessive allele for expression ( they have 1 X and 1 Y ) instead of 2

for females, they need to carry two (x and x) and when males have been x linked recessive condition, they have inherited it form their mother

Question 21

what is epistasis

Answer 21

it is the interaction between 2 genes where one gene masks the expression of the other gene in the phenotype

Question 22

what is the suppressing gene called

Answer 22

it is called the epistatic gene

Question 23

what is the suppressed gene called

Answer 23

the hypostatic gene

Question 24

what can epistatic interactions be

Answer 24

dominant or recessive

Question 25

what is a dominant epistatic interaction

Answer 25

the dominant allele ( 1 or 2 copies) of the epistatic gene masks the expression of hypostatic

Question 26

what is a recessive epistatic interaction

Answer 26

two copies require to mask the expression of the hypostatic gene

Question 27

what is chi-squared test

Answer 27

it is a statistical test that determines the probability of an unexpected result being due to chance or being significant

we use chi-squared if the data used is categorical and we are comparing the observed results with the expected results

Question 28

when is the result of a chi - squared test significant

Answer 28

it is significant when the calculated value is more than the critical value

Question 29

what is the gene pool

Answer 29

all the alleles pf all the genes within a population at one time

Question 30

what is population

Answer 30

all the individuals of one species in one area at one time

Question 31

what is allele frequency

Answer 31

the proportion of an allele within the gene pool

Question 32

what are the assumptions of the Hardy - Weinberg equation

Answer 32

It assumes that there will be no change in the allele frequency between generations within a population, so it is not perfectly accurate:

the assumptions are:
no migration to introduce or remove alleles from the population
no mutation to create new alleles
no selection favouring particular alleles
mating is random (no inbreeding)
the population is large

the assumptions impair the accuracy of the equation

Question 33

what is the equation useful in estimating

Answer 33

the allele frequency

Question 34

what is the Hardy - Weinberg equation formula

Answer 34

p squared + 2pq + q squared where:
p+q = 1
-p = the frequencey of the dominant allele
-q = is the frequency of the recessive allele
-p squared = the frequency of the homozygous dominant genotype
2pq = the frequency of the heterozygous genotype
q squared = the frequency of the homozygous recessive genotype

Question 35

what type of questions are genetic pedigree diagrams

Answer 35

1. the condition s caused by recessive/ dominant/ sex-linked allele
   Explain the evidence for this given in the diagram
2. How does the diagram prove the condition is most likely to be caused by a recessive/ dominant allele?
3. what are the possible genotypes of individual x in the diagram

Question 36

what are patterns to spot in genetic pedigree diagrams

Answer 36

1/ evidence that the condition is caused by a recessive allele

two parents who do not have the condition have a child who does have the condition
Therefore both parents must be carriers of the recessive allele, but due to the presence of a dominant allele, they do not have the condition themselves

2/ evidence the condition is caused by a dominant allele

two parents who do not have the condition have a child who does not have the condition therefore, both parents must be carriers of the recessive allele, but due to the presence of dominant alleles, they have the condition themselves

Question 37

what is the best way to model genetic pedigree diagrams

Answer 37

Give evidence

then explain

Question 38

how can we disprove sex linkage

Answer 38

if the condition is caused by a dominant allele, any affected father would pass on the condition to any daughter they have as the daughter is XX and one of the X is from the father’s XY

if this is not the case and the daughter is unaffected then it is not sexed linked

Question 39

what happens when you do a monohybrid cross with two parents involving codominant alleles

Answer 39

you would expect to see a 1:2:1 ratio in the offspring

Question 40

what are the phenotypic ratios for epistatic genes

Answer 40

recessive epistatic alleles:

-if you cross a homozygous recessive parent with a homozygous dominant parent you will produce a 9:3:4
dominant both: dominant epistatic: recessive other

dominant epistatic alleles:
crossing a homozygous recessive parent with a homozgous dominant parent will produce a 12:3:1 phenotypic ratio of dominant epistatic: recessive episatic: dominant other: recessive both in the F2 generation