Section 7 Chapter 17 Inherited change

Define the following:

Genotype, phenotype, allele, locus, homozygous, heterozygous, dominant, recessive, codominant, autosomal linkage, epistasis, gene pool, allele frequency:

Definitions:

Epistasis: The expression of one gene masks the effect of another gene

Monohybrid inheritence:

Described the inheritance of one gene.

Dihybrid inheritence

The inheritence of two genes.

To test the significance through the dihybrid cross:

• Chi squared test is used to test for significance 

• If the p< 0.05 we reject H0, there is sufficient evidence that the difference is significant 

• There is less than 0.05 probability that this has occurred due to chance 

• The degrees of freedom: the total phenotypes - 1 (so in image there are 3 degrees of freedom)

Key points for codominance:

• When both alleles are expressed, as both are dominant.

Key points for autosomal linkage:

• An autosome is a chromosomes that is not a sex chromosome, when two or more genes appear on a chromosome this is called an autosomal linkage

• Autosomal linkage without crossing over, 3:1

• Autosomal linkage with crossing over, 9:3:3:1

• Autosomes in homologous pairs always contains the same genes, may contain different alleles.

• Why is there not 3:1 ratio?

  • Becuase during meosis crossing over took place, so there is a new combination of gametes resulting in different ratios of phenotypes.

Sex linkage:

XX = Female

XY = Male

Based on sex-linked genes, genes located on a sex chromosome, so allele expression depends on the sex of an individual. For example, more men than women are red-green colour blind.

There is no alleles on Y chromosome!

Key points for Pedigree analysis diagrams:

They show the inheritance of a particular phenotype over several generations.

Key information for Epistasis:

Nice little summary:

Here:

1 mark: genes are linked

2nd mark: crossing over has taken place (4 geneotypes) OR crossing over has not taken place (2 genotypes)