Genetics

Question 1

Definition of Gene?

Answer 1

A sequence of bases on a DNA molecules that codes for a polypeptide

Question 2

Definition of allele?

Answer 2

A different version/form of a gene

Question 3

Definition of genotype?

Answer 3

The genetic constitution of an organism

Question 4

Definition of phenotype?

Answer 4

The physical characteristics determined by the genotype and the environment

Question 5

Definition of dominant?

Answer 5

Expressed in the phenotype if present in the genotype

Question 6

Definition of recessive?

Answer 6

Only expressed if homozygous in the genotype

Question 7

Definition of co-dominant?

Answer 7

Alleles that are both expressed in the genotype

Question 8

Definition of Locus?

Answer 8

The fixed position of a gene on a chromosome

Question 9

Definition of Carrier?

Answer 9

Carrying an allele but not expressing it in the phenotype but will pass it on to the offspring

Question 10

Homozygote vs Heterozygote?

Answer 10

Two copies of same gene

One copy of 2 different genes

Question 11

Monohybrid inheritance?

Answer 11

Inheritance of a characteristic controlled by a single gene

Question 12

Example of co-dominance?

Answer 12

Sickle Cell anaemia
Homozygous for normal haemoglobin don’t have the disease
Homozygous for sickle haemoglobin have sickle-cell anaemia
Heterozygous have the sickle cell trait but have some normal haemoglobin

Question 13

Dihybrid inheritance?

Answer 13

Two genes being inherited at the same time

Question 14

Predicted ratios for inheritance?

Answer 14

Monohybrid - Homozygous dominant x homozygous recessive = 3:1 - dominant is most abundant
Dihybrid - Homozygous dominant x homzygous recessive - 9:3:3:1 - Dominant both most abundant - recessive both the least
Co-dominant - Homozygous for one allele x homozygous for the other - 1:2:1
If different then maybe sex-linkage, autosomal linkage or epistasis is present

Question 15

Sex-linked characteristic?

Answer 15

When the allele what codes for the characteristic is located on a sex chromosome

Question 16

Y vs X

Answer 16

Females = XX
Males = XY
Y is smaller and carries fewer genes - most genes on sex chromosomes are only carried on the X-chromosome (X-linked genes)

Question 17

Males vs Females

Answer 17

Males only have one X chromosome - only have 1 allele for sex-linked genes
Males more likely to show recessive phenotypes for sex-linked genes

Question 18

Sex linked diseases?

Answer 18

Colour blindness and haemophilia - X linked disorders

Question 19

What is an autosome?

Answer 19

Chromosome that isn’t sex linked

Autosomal genes are genes located on the autosomes

Question 20

Autosomal linkage?

Answer 20

Genes on the same autosome are said to be linked
On same autosome so stay together during the independent segregation of chromosomes in Meiosis I
Alleles will be passed on to offspring together
Will only not happen if crossing over splits them up
The more closely they are together on the autosome the more closely they are linked - crossing over is less likely to split them up
IF they are linked then you won’t get the predicted ratio
Higher proportion of the offspring will have their parents genotype and phenotype - how to spot

Question 21

What is an epistatic gene?

Answer 21

When the allele masks the expression of the alleles of other genes

Question 22

What is the null hypothesis?

Answer 22

Theres no significant difference between the observed and expected results

Question 23

Chi Squared equation?

Answer 23

X^2 = THE SUM OF (O-E)^2 / E

Question 24

Finding the value of X^2

Answer 24

Need to compare to a critical value
The value where X^2 corresponds to a 0.05 (5%) level of probability that the difference between the observed and expected result is due to chance
If x^2 value is the same or greater than the critical value then the null hypothesis must be rejected
To find the critical value:
degrees of freedom (number of phenoypes) - 1
Then scroll to 0.05 (5%)

Question 25

Explaining results of gene linkage?

Answer 25

Which genes are linked?
Which parents produce which offspring the most?
Crossing over produces somes/few other gamets
Fewer of the outlying gametes