The mother who married her son, then her daughter.

An Oklahoma woman has avoided jail time for marrying her mum after pleading guilty to incest.

The 26-year-old woman, Misty Spann, was sentenced to 10 years probation for the March 2016 wedding to her 44-year-old biological mum Patricia Ann Spann, Tulsa World reports.

Misty had been raised by her grandmother after her mum had lost custody of her and her two siblings. But in 2014 the pair reconnected. And that’s when they “hit it off”.

Within two years, they married.

While we don’t know the state of the marriage in the time they were together, Misty and Patricia were investigated by the Department of Human Services in August this year.

While her daughter will not serve time in prison, Patricia is due to face court for the crime in January.

What makes this story even more bizarre, however, is that this is not Patricia Spann’s first incestuous relationship; in 2008, she married another one of her children, her biological son. The union was annulled 15 months later, after her son/husband deemed it was wrong to be in an “incestuous” marriage.

Sadly, Patricia's third child, Cody, says his siblings have been manipulated by their mother into romantic relationships with her.

“I think she's worthless she put my sister into this," Cody Spann told local news website KSWO. "She forced my sister into this, there's a lot of people that know it. For you to want to put your own daughter through this, what kind of person are you?"

For most, this kind of relationship isn't just hard to comprehend - to many it's simply sickening - but there's actually research that supports an overwhelming attraction relatives who meet as adults for the first time feel, known formally as Genetic Sexual Attraction.

First, a 2011 University of Illinois study published in the Personality and Social Psychology Bulletin found, people appear to be drawn to others who resemble their kin or themselves.

However, most of us are desensitised to sexual attraction to our relatives later in life by living together in early life. This is what's known as the "Westermarck" effect — named after sociologist Edward Westermarck.

Relatives who don’t live together miss out on the daily events that prevent such attraction from occurring– so that, in effect, the ‘Westermarck’ effect doesn’t have a chance to work in those situations, as Canadian GSA expert and counsellor Dianne Mathes told CBC News.

Incest is a crime against nature, many would argue. But what makes it a crime punishable by jail time?

In Australia, it is illegal to marry your child (including step-child), grandchild, parent or grandparent or sibling in all states and territories, but sexual intercourse is what defines incest.

An article on the Australian Institute of Family Studies explains that incest laws vary from state to state, but are largely used to penalise non-consensual sex or where a victim makes a complaint against their family member. Crimes where the child is a minor are different of course, and treated as child sexual abuse.

"The fact that the crime of "incest" applies both to consensual and non-consensual sexual acts can make it particularly inappropriate," the government website explains.

"Some people who have been raped or sexually assaulted by close relatives feel that a crime which fails to distinguish between consensual and non-consensual sexual contact is inappropriate and offensive."

Listen: Your relationship with your mother doesn't need to be sexual to be toxic. (Post continues...)

The article explains that crimes of rape or sexual assault between family members are often charged as incest, because it is often easier to prove the two are related than that the sex was non-consensual.

The crime of incest with an adult child, sibling or parent varies across the states and territories. For instance, in Victoria there is a maximum penalty of 25 years in you are the parent or grandparent, but up to five years as the child (or step-child). Meanwhile, in NSW, anyone who has intercourse with a 'close family member' over the age of 16 could face up to eight years jail.

On their website, Sydney Criminal Lawyers clarify, "While these penalties may seem heavy, it’s important to remember that they represent the absolute maximum penalty that can be imposed – therefore they will only apply in the most serious of cases."

The Victorian Law Reform Commission adds, "Although it is not common for the person who reports the abuse to be charged as a co-offender... the possibility of charge may act as a disincentive for an adult victim to report the offence."

In Australia, incest laws are largely used to protect victims of sexual abuse. Meanwhile, under Oklahoma law, marrying a close relative is considered a punishable form of incest whether the relationship is sexual or not, carrying a maximum penalty of a year's jail.