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Flashcards in Genetics Deck (25):

Definition of Gene?

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


Definition of allele?

A different version/form of a gene


Definition of genotype?

The genetic constitution of an organism


Definition of phenotype?

The physical characteristics determined by the genotype and the environment


Definition of dominant?

Expressed in the phenotype if present in the genotype


Definition of recessive?

Only expressed if homozygous in the genotype


Definition of co-dominant?

Alleles that are both expressed in the genotype


Definition of Locus?

The fixed position of a gene on a chromosome


Definition of Carrier?

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


Homozygote vs Heterozygote?

Two copies of same gene
One copy of 2 different genes


Monohybrid inheritance?

Inheritance of a characteristic controlled by a single gene


Example of co-dominance?

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


Dihybrid inheritance?

Two genes being inherited at the same time


Predicted ratios for inheritance?

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


Sex-linked characteristic?

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


Y vs X

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)


Males vs Females

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


Sex linked diseases?

Colour blindness and haemophilia - X linked disorders


What is an autosome?

Chromosome that isn't sex linked
Autosomal genes are genes located on the autosomes


Autosomal linkage?

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


What is an epistatic gene?

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


What is the null hypothesis?

Theres no significant difference between the observed and expected results


Chi Squared equation?

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


Finding the value of X^2

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%)


Explaining results of gene linkage?

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