Ch4 - Modification of Mendelian Ratios

What are the 2 postulates of Mendelian genetics?

1. genes are present on homologous chromosomes

2. chromosomes segregate from each other and assort independently during gamete formation

When are mendelian ratios modified

When gene expression does not adhere to dominant/recessive or when more than one gene controls a trait.

sex-limited

restricted to one sex; expressed in only one sex (ex: beard growth or egg production)

sex-influenced

how the same genes act differently in males and females due to hormonal differences.

What can vary the expression of traits?

the environment to which a gene, cell, or organism is exposed.

Extranuclear inheritance

the inheritance of genes located outside the cell nucleus, specifically in organelles like mitochondria and chloroplasts, and is also known as cytoplasmic inheritance

What are alles?

Alternate forms of a gene; they may arise via mutations

What is a wild-type allele?

An allele that occurs more frequently in the population, and it may often, but not always, be dominant.

what is a mutant allele?

an allele that contains genetic information and often specifies an altered gene product.

What do new phenotypes result from?

mutations in the activity of a cellular product (e.g., protein) of a gene; there are also neutral mutations.

Gain-of-function mutation

may increase the function of a wild-type protein by increasing its quantity; it may be positive or negative.

loss-of-function mutation

may change a protein’s structure and thus its affinity for molecules; complete loss results in a null allele.

Null Allele

a nonfunctional or absent version of a gene, usually caused by a genetic mutation, that results in no detectable protein product or activity.

e+/e+ or +/+

gray homozygote (WT)

e+/e or +/e

gray heterozygote (WT)

e/e or e/e

ebony homozygote (mutant)

What is incomplete (or partial) dominance

Where either allele’s are dominant

In terms of snapdragon flowers, what is an intermediate color?

results from a cross between parents with contrasting traits (red X white)

What happens in codominance?

Where two alleles of a gene produce different products (Heterozygote); both wheels and heterozygote fully and equally expressed. Example: human blood type AB.

Is codominance different or the same from incomplete dominance

different 

What happens in incomplete dominance?

Neither allele is completely dominant, so the heterozygote shows an intermediate (blended) phenotype. Example: snapdragon flowers, expressing a blend of red and white, producing pink flowers.

What is a recessive lethal allele?

Where homozygous from extensiveness will result in death and is fatal.

What is a dominant lethal allele?

where homozygous dominance will result in death and is lethal.