Inheritance

Question 1

gene

Answer 1

sequence of nucelotides tht code for polypeptides = characteristics.

Question 2

allele

Answer 2

variation of the gene. we have 2 alleles, for each gene, one from each parent.

Question 3

locus

Answer 3

a fxes position of a gene on a chromosome. Alleles are found on the same locus of a gene on each chromosome in the pair.

Question 4

is it always true that dominant alleles are more common
give an example.

Answer 4

no it is a myth. cos thos dominant alleles may be very rare, a population where most are recessive.
eg- polydactyly - born with 1 extra finger. the genotype includes a dominant allele, however in comparison to people with 5 fingers, people with 6 are not so common.

Question 5

genotype

Answer 5

the genetic makeup of an organism, representing the combination of alleles. can be homozygous or heterozygous.

Question 6

phenotype

Answer 6

observable characterisic.

Question 7

co-dominant alleles

Answer 7

when both alleles are expressed in the heterzygote phenotype, there are no recessive alleles, when talking about co-dominance.

Question 8

give an examples of codominance

Answer 8

1. blood groups AB - alleles = I^A I^B

Question 9

explain how codominance affects the phenotypes if both parents are heterozygous for sickle cell aneamia.
and state the ratio.

Answer 9

homozygous - heamoglobin - H^N H^N
homozygous - sickle cell aneamia - H^S H^S
heterozygous - sickle cell - H^S H^N
- so here some cells are sickle shaped and some arent.

2 heterozygous parents result in the ratio - 1:2:1
1 - unaffected
2 - sickle cell trait (heterozygous)
1 - Sickle cell aneamia (homozygous)

Question 10

give an example where a gene may have multiple alleles (more than 2)

Answer 10

Blood groups AB, A, B, and o, have the following alleles -
I^A, I^B, I^o
here A and B are dominant and o is recessive.

Question 11

epistasis and what are the different types.

Answer 11

only occurs hen 2 or more genes contribute to the same phenotype = when the expression of one gene masks or modifies the expression of another gene (aka the hypostatic gene) at a different locus.

different types include -
- dominant epistasis
- recessive epistasis
- duplicate (redundant) gene action.

Question 12

what is the expected ratio when more than 1 characteristic is inherited from 2 different genes.
Using a dihybrid cross

Answer 12

9:3:3:1

Question 13

what is the ratio observed when you cross 2 copies of recessive epistatic alleles. (dihybrid cross)
(homo recessive x homo dominant)

Answer 13

9:3:4
(dominant both:dominant epistatic recessive other:recessive epistatic.)

Question 14

what is the ratio observed when you cross 2 copies of dominant epistatic alleles. (dihybrid cross)
(homo recessive x homo dominant)

Answer 14

12:3:1
(dominant both:dominant epistatic recessive other:recessive epistatic.)

Question 15

polygenic inheritance

Answer 15

involves the interaction of multiple genes to control the expression of a single trait.
- the cumulative effect of multiple alleles at diferent gene loci control the gene expression.

Question 16

give an example of epistasis

Answer 16

windo’s peak is controlled by one gene whilst the gene for baldness is controlled by another.
if you have the alleles for baldness, it does’nt matter if you have the alelle for a widow’s peak or not cos either way you will be bald.

• the baldness genes are epistatic for the widow’s peak gene.

Question 17

what are modifier genes. give an example.

Answer 17

they dont produce a trait themselves, however they influence the expression or severity ot traits produced by other genes.

• eg in cystic fibrosis, certain modifier genes can influnece the severity of lung disease amongst people with the same CFTR mutation.

Question 18

describe a relationship between mutations and epistais

Answer 18

the effect of a mutation on one gene might be masked or altered by a mutation in another gene.

Question 19

describe a regulatory mechanism that can mask the expression of another gene and is this the same as epistasis?

Answer 19

No this isnt the same as epistasis.
- when the repressor protein of one gene binds to the promotor of another gene, the transcrption is inhibited. and the expression is essentially ‘masked’
- but can’t be the same as epistasis, which is just the interaction, that affects phenotypic expression.

Question 20

describe complementary gene interaction

Answer 20

when 2 different genes work together to form a specific trait. the presence of at least one dominant allele at both gene loci is needed to express the phenotype.

• if one is homozygous recessive, then it may be masked = different phenotype.

Question 21

give an example, of complementary gene interaction in the flower colour in sweet peas. and give the phenotypic ratio.

Answer 21

Take for example the genes C and P.
alleles include
C and c = C needed for the production of the colour precursor.
P and p = P needed for the conversion of precursor into the final pigment.
to get a purple colour both dominant C and P are needed
- any other genotypes will give a white flowered phenotype. (homozygous recessive)

ratio = 9:7 purple:white

without the C and P alleles, this pathway cannot continue, showing how they are complementary to each other.

Question 22

what is supplementary gene interaction

Answer 22

genes that contain non-alleic pairs of genes. they both have an effect on the triat.
- 1st gene is dominant and can be expressed on it’s own among the non-alliec genes.
- 2nd gene is also dominant but only expresses it when the first gene is present.

Question 23

gene redundancy (in terms of genetic interactions)

Answer 23

presence of multiple genes with similar functions, if one gene is mutated or inactive, the other redundant genes can compensate and maintain overallu function.

Question 24

pleiotropy

Answer 24

when a single gene can affect multiple phenotypic traits, eg - a gene associated with a certain enzyme may impact several biochemical pahtways.

Question 25

incomplete dominance

Answer 25

gene interaction, in which both alleles of a gene at a locus are partially expressed - resulting in an intermediate or a new phenotype.
(forming a hybrid phenotype)

• heterozygotes show an intermeditate phenotype.

Question 26

give an example of incomplete dominance

Answer 26

Curly hair - CC
Wavy hair - cc
someone with 1 allele for curly hair and 1 allele for straight hair will have wavy hair.

Question 27

other than genetics what else can influence inheritence

Answer 27

environmental factors, play a key role in the nature-nurture influence. they

Question 28

describe the law of segregation

Answer 28

each person has 2 alleles for each trait, from each parent.
- during gamete formation, these alleles seperate.
- now each gamete only has one allele.

Question 29

law of independent assortment.

Answer 29

genes located on different chromosomes, assort independently during meiosis (gamete formation).
- applies to genes for different traits.

Question 30

what are non-alleic interactions, and give examples of these genetic interaction.

Answer 30

intereactions between genes that are not on the same chromosome.

• epistasis, complementary gene interaction and simple interaction.

Question 31

give examples of alleic interactions

Answer 31

incomplete dominance (1:2:1),
codominance, over codominance, lethal factor, multiple alleles.

Question 32

what is simple gene interaction.
ratio

Answer 32

seen in a dihyrid interactions.
when the same characteristic is influenced by 2 non-alleic gene pairs.
combination - homozygous dominant and homozygous recessive.
- 9:3:3:1

Question 33

what is over codominance

Answer 33

when the F1 heterozygotes have more extreme phenotypes than either of their parents.

Question 34

difference between codominance and incomplete codominance

Answer 34

codominance - has the 2 parent phenotypes are expressed together in their offsprings.
- blood groups
but incomplete has a hybrid of the parents phenotypes, resulting in a new phenotype.
- hair (wavy = curly + straight)

Question 35

what are sex linked characterisitics

Answer 35

when the gene for the characteristic is found on a sex chromosome (X or Y).
so genes found on the X chromosome are called x-linked.

Question 36

which chromosome X or Y carries more genes

Answer 36

X is a larger chromosome, so most genes are only carried on X

= X-linked genes.

and X-linkage is more common than Y-linkage

Question 37

why are males more susceptible to express the recessive phenotypes.

(hemizygosity applied here)

Answer 37

cos males only have one X chromosome, and for most sex linked chromosomes are found on X.
they are expressed even tho recessive.

• so males are more likely to recessive phenotypes than females.

Question 38

what is hemizygosity

Answer 38

when recessiveness and no dominance have no role on the allele. will be expressed either way.

• eg - recessive alleles on the X chromosome, for X-linked characteristics in men.

Question 39

give examples of X-linked inheritence
what is the inheritence pattern like.

Answer 39

heamophillia, blindness and muscular dystrophy.

passed from fathers only to their daughters and from mothers to both son an daughter.

Question 40

give examples of Y-linked inheritence

Answer 40

inherited exclusively to the son via the father.
- eg - webbed toes
- Hypertrichosis (hairy ears)

Question 41

what are autosomes
and what are autosomal genes.

Answer 41

1. non-sex chromosomes
2. genes located on the autosome.

Question 42

what is autosomal linkage. and how does it link to inheritence.

Answer 42

when 2 genes on an autosome (their locus) are closer togehter, they are said to be linked.
- the more closer linked they are (or shorter the distance between each loci) the more likely that they are inherited together.

Question 43

what could seperate genes on autosomes, and what can overcome this seperation.

Answer 43

independent assortment (in Meiosis 1) and crossing over to form recombinant chromosomes, can sperate genes on chromosomes when bivalents are formed from homologous chromosomes.

closer loci of the genes = linked = reduces the possibility of the genes getting seperated.

Question 44

what is the likely phenotype of the genotype if the autosomally linked genes arent seperated.

compare to a F2 gen of a duhybrid cross.

Answer 44

F2 in a dihybrid = 9:3:3:1

however here, the phenotypic ratio is more similar to that of a monohybrid cross 3:1 cos they both are inherited together.
- a higher proportion of the offsprings will have the parents heterozygous genotype and phenotype.

Question 45

how can genetic maps and indication of genes on a chromosomes be made.

Answer 45

through the process of mapping genes.
- by looking at the frequency of crossing over between linked genes is proportional to the physical distance between their loci on the chromosome.

Question 46

what can be done to determine if a trait is heterozygous or homozygous

Answer 46

using a test cross, either monohybrid or dihybrid.

Question 47

what is the difference between co-dominance and complete dominance

Answer 47

complete c = only one allele in the genotype is seen in the phenotype. (blood group A complete dominance over group O).
- codominance = both alleles in the genotype are seen in the phenotype. (AB blood group)

Question 48

pedigree

Answer 48

diagram following inheritence patters in a family.

Question 49

expected gentoypic and phenotypic ratio when 2 heterozygous - Aa x Aa crossed.

Answer 49

genotypic = 1:2:1
1homo dominant : 2 hetero : 1 homo recessive.

phenotypic = 3:1

Question 51

What do F1 hybrids show

Answer 51

They exhibit uniform phenotypes, that reflect the dominant trait.
All offsprings are heterogenous