3.7.1 Inherited Change Flashcards
What is a recessive allele?
An allele that is only expressed an individual has two copies of that allele. Will not be expressed in a heterozygous individual.
What is a loci?
Position of a gene on a chromosome
What is a linked gene (autosomal)?
Linked genes have their loci on the same chromosome and so stay together during independent assortment and are passed on to offspring together
How can autosomal linked genes be separated ?
By crossing over to produce “recombinant” gametes
What would be the ratio in the F2 generation for a dihybrid cross with no linkage
9:3:3:1
What would be the ratio in the F2 generation for a dihybrid cross where the 2 dominant alleles are perfectly linked
3 to 1
What makes two genes more closely linked?
Having their loci closer together on the same chromosome
What chromosomes do males and females have
Female = XX, Male = XY
In birds the sex chromosomes are called Z and W. Which way around is it? (off spec but commonly given as info for application questions)
Female = ZW, Male = ZZ
Define sex-linkage
when the locus of a gene is on a sex chromosome
Why are males more likely to show sex-linked recessive phenotypes than females ?
They only have one X chromosome, so they often only have one allele for sex linked genes. As they only have one copy, they express the characteristic of this allele even if it is recessive
Give examples of X linked disorders
Colour blindness and haemophilia
Define heterozygote
An individual with different alleles of a gene at a particular locus
Define allele
Version of a gene
Define genotype
The alleles a person has
Define phenotype
The characteristics displayed by an organism
Define dominant
An allele that is expressed in the phenotype even when there is only one copy
Define carrier
If a recessive allele can cause a disease, a carrier is someone who is heterozygous for the gene. They wont have the disease but they carry a copy of the allele for the disease
Define co-dominance
Both alleles influence the phenotype because they are both expressed equally
In a cross between Red (RR) and white (rr) cows with codominant inheritance what would be the pheotypic ratio of the offspring
100% Roan (Rr)
In a cross between two Roan cows (Rr) what would be the ratio of the offspring?
25% white (rr), 50% roan (Rr) , 25% red (RR)
Define homozygote
An organism that has 2 copies of the same alleles for a characteristic
What is monohybrid inheritance?
The inheritance of a single characteristic controlled by different alleles
What is dihybrid inheritance?
The inheritance of 2 characteristics controlled by different alleles (you use a 4x4 punnet square)
Define ‘epistasis’
When the allele of one gene affects or masks the expression of another in the phenotype
Which statistical test do you use to see if the offspring produced are significantly different to those predicted by a genetic cross?
Chi-squared test
What is the chi-squared test used to test for
To see if observed frequences are signficantly difference from expected frequencies (e.g. in genetic crosses)
how do you use this formula
In a chi-squared test, if the P value is greater than 0.05, what does this mean?
The null hypothesis is rejected, there is a significant difference between the observed and the expected frequencies. This difference is not due to chance.
