Genetics Chapter 4

Mendel’s two postulates:

1. Genes are located on chromosomes.

2. Chromosomes segregate and go through independent assortment during gamete formation.

Where are sex linked genes located?

On X or Y chromosomes

What are the chromosomes for female?

XX

What are the chromosomes for male?

XY

What is sex limited inheritance?

The understanding that a gene can be present in both sexes, but the trait is expressed only in one sex.

What is Polygenic Inheritance?

Multiple genes affecting one trait.

What is an allele?

An alternate form of a gene

What is a wild type allele?

An allele that occurs more frequently within a population. Often but not always dominant

What is a mutant allele?

An allele that contains modified genetic information.

What are the 3 types of mutant alleles?

1. Loss of Function Mutation

2. Gain of Function Mutation

3. Neutral mutation

What is a Loss of Function Mutation?

When an allele stops working normally or stops working all together.

What is a Gain of Function Mutation?

It enhances the function of a wild type allele, usually causing it to be dominant.

What is a Neutral Mutation?

When the genes produce no changes in the phenotype.

What is a Null Allele?

An extreme case of a Loss of function mutation where the allele loses all function.

Essential Genes

Absolutely needed for survival

Lethal Allele

Had the potential to cause death

What creates a lethal allele

A mutation in the essential genes

Recessive lethal allele

Can only survive if heterozygous or if there is a wild type allele present

Dominant lethal allele

Only needs one copy to cause death

Homozygous recessive lethal allele

May result in a mutant phenotype when present with heterozygotes

Proband

Starting point of a genetic study

Dominant autosomal allele

It’s dominant on one of the 1-22 chromosomes not the sex chromosomes

What are the sex chromosomes

X and Y

What are autosomes

Chromosomes 1-22

How many chromosomes do humans have?

23

Is is possible to receive a gene or genetic disorder from only one parent?

Yes if the gene or disorder is sex limited

What are sex limited genes?

Genes that may only be present on the X or Y chromosome thus only presenting or passing through one gender.

What is gene interaction?

When multiple genes can influence one phenotype.

What is epistasis?

2 genes may affect the same trait/characteristic, but one may mask or block the other from being expressed.

What is an example of Epistasis?

The Bombay phenotype

What is the Bombay phenotype?