Inheritance Flashcards
Di-hybrid cross
Inheritance of two different characteristics controlled by two different genes
Co-dominance
Both alleles in a heterozygous organisms are expressed in the phenotype
Define an allele
One of the different forms of a gene
Dominant
The allele of a heterozygous organism that is expressed in the phenotype
Only one copy needed
Recessive
In a heterozygous state the allele is NOT expressed, only expressed if homozygous recessive.
Define a gene
A base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule
Define phenotype
The expression of an organism’s genetic constitution and its interaction with the environment.
Autosomal linkage
Two Genes carried on the same autosome- non-sex chromosome
What is the effect of genes being closer together on the same autosome?
The closer together the more closely linked they are
Less likely to be split up in meiosis, crossing over
Therefore higher proportion of gametes and offspring will have parents geno/phenotypes
Epistasis
The interaction of non-linked genes when one affects/ masks the expression of another
What is a Chi-squared test?
Statistical test used to find out wether there is a significant difference between observed and expected results.
Or difference is due to chance- sampling effects
Used on categoric data, frequencies
Null hypothesis, alternative hypothesis
Is Chi value > critical value at p=0.05
Then Reject Ho
Sex linkage
Genes which have a locus on a sex chromosome
Most often x linked
Males
XY
So recessive X-linked genes will expressed even if only one copy present
Females
XX
So recessive X-linked genes will only be expressed if the organism is homozygous recessive
Multiple alleles
More than two alleles (versions) of the same gene
Why are observed results not similar to predicted?
Small sample size- high influence of chance
Fertilisation of gametes is a random process
Lethal genotypes
linked genes
Why is a chi-squared test used?
To determine the probability; [Accept: Likelihood]
Of the results being due to chance; [Accept: Coincidence]
Effect of autosomal linkage
They will stay together during independent segregation
Assume no crossing over
All linked genes will stay together during meiosis
So linked genes are passed onto gametes and the offspring together
Higher proportion of offspring will have parents
Geno/phenotype
Evidence of autosomal linkage
when a di-hydrid cross results in production of offspring/ gametes which are predominately 2 genotypes
identify which alleles are linked- which are the 2 most common gametes?
production of most gametes- therefore most offspring produced like to have the geno/pheno types of parents- inherited together
What dose the Hardy-Weinberg Principle predict?
predicts allele frequencies will not change in a population from one generation to the next
Conditions for the Hardy-Weinberg Principle
mating is random no death no immigration large population no natural selection
Hardy equation to predict allele frequencies
p+q=1
where p is freq of domination, q is freq of recessive
Hardy equation to predict geno and phone type frequencies
p^2 +2pq+ q^2=1
p^2 homozygous dominat
q^2 homozygous ressecive
2pq hetrozygous
