Bio Non-Mendelian Genetics

Non-Mendelian Genetics

the inheritance of traits that have a more complex genetic basis than one gene with two alleles and complete dominance

Incomplete dominance

form of gene interaction in which both alleles of a gene are partially expressed

• Neither allele is dominant

• When an organism is heterozygous for a trait, it shows a third phenotype

• ex. a red and white flower breed, resulting in a pink flower

Codominance

a type of inheritance in which two versions (alleles) of the same gene are expressed separately to yield different traits in an individual

• Codominant is equal dominance

• Alleles have an equal effect in individuals and are equally detectable

• When an organism is heterozygous for a trait, it shows a third phenotype

Multiple Alleles

the presence of three or more alleles for a given gene

What are Polygenic characteristics controlled by?

more than one gene, and each gene may have two or more alleles. The genes may be on the same chromosome or on nonhomologous chromosomes

If the genes are located close together on the same chromosome, what happens?

they are likely to be inherited together. However, it is possible that they will be separated by crossing-over during meiosis, in which case they may be inherited independently of one another.

Sex-linked traits

traits controlled by genes located on the X or Y chromosome

• The X and Y chromosomes are the sex chromosomes

Female vs Male chromosomes

• Females have a homologous pair of X chromosomes (XX)-

• Males have an XY chromosome pair

X and Y chromosome similarity

Y chromosomes contains a small region of similarity to the X chromosome, but the Y is

• much shorter

• contains fewer genes

Why are males said to be hemizygous?

they have only one allele for any X-linked characteristics

• This makes the descriptions of dominance and recessiveness irrelevant for XY males

Y-linked genes

Genes on the Y chromosomes

• The few on the Y have to do with male-only traits and can only be passed from father to son

• Example: Hypertrichosis Pinnae Auris is a genetic disorder in humans that causes hairy ears

X-linked genes

X chromosomes

Who do X-linked traits most often affect and why?

Males because females have 2 X-chromosomes, so dominant/recessive traits still apply.

Example of sex linked traits

• Examples: Hemophilia and Color-blindness

• Hemophilia is a recessive disease where one of the normal blood clotting factors is not produced, resulting in prolonged bleeding from minor cuts and injuries and swollen joints

• Females can be normal, carriers, or have the disease

• Males will either have the disease or not (they can never be carriers)