Sex Linked Inheritance

Wait…. What????? What’s a “mosaic”? Remember the FLUID MOSAIC MODEL???? The Plasma Membrane P.S. What is a Plasma Membrane? An individual (organism, artwork, organelle) made up of smaller, different ”pieces”… So, in a way, WE ARE MOSAICS, too!

Calico Cats Calico Cats can ONLY BE Female!

Why???? Because a cat’s fur color is linked to two different alleles on the “X” chromosome And…For a cat to have more than two colors… It must have TWO X CHROMOSOMES!

Sex-Linked Inheritance Sex-Linked Inheritance means that a gene (or multiple genes) are carried on one of the sex chromosomes

Sex-Linked Inheritance Remember, Females have XX and Males are XY. The Y has very few genes - mainly those that contribute to male characteristics. (Only about 87 genes total.) The X much more genetic information – for gender and other characteristics. (About 2050 genes!)

Sex-Linked Inheritance Some genes for a disorder/disease are located on one of the sex chromosomes If the gene is linked to the “Y” chromosome, women will not have the disorder. Why? _________________________________ If the gene is linked to the “X” chromosome, and it is recessive, women will not express the disorder. Why? ______________________________________ If the gene on “X” is dominant… both will express it!

Who is usually affected by Sex-Linked Disorders? MEN! Genes for certain traits are on the X chromosome only… Since Men only have one X chromosome then they are more likely to have the disorder Women are somewhat protected since they have two X chromosomes and are less likely to inherit receive disorders. If women receive a recessive gene on one X chromosome, they are called “carriers” because they “carry” the gene but don’t express the disorder

Sex-Linked Disorders Affected males never pass the disease to their sons Men give their “Y” to their sons! Affected males pass the defective X chromosome to all of their daughters, who are described as carriers This means they carry the disease-causing allele but generally show no symptoms Female carriers pass the defective X chromosome to… half their sons (affected by the disease) half their daughters (who are carriers) The other children inherit the normal copy of the chromosome

How do you solve Sex-linked Problems? If Red eyes are dominant and sex-linked, show the cross between a homozygous red eyed female and a white eyed male. You determine which trait (or disorder) is dominant or recessive Set up a punnett square using XX for females and XY for males. Assign alleles for X only! Solve as usual, keeping in mind that the Y chromosome has no allele! Genotypes: XRXr , XRY Phenotypes: All offspring have red eyes.

Your Turn! Hemophilia is a sex-linked trait where XH gives normal blood clotting and is dominant to the hemophilia allele Xh Identify the genotypes of… 1) a woman with normal blood clotting whose father had hemophilia 2) a normal man whose father had hemophilia. What is the probability that a mating between these two individuals will produce a child, regardless of sex, that has hemophilia?

Set up the Punnett Square! - a woman with normal blood clotting whose father had hemophilia  XHXh - a normal man whose father had hemophilia  XHY Genotypes: Phenotypes:

What are some X-linked disorders? ALD Hypertrichosis Duchenne muscular dystrophy Hunter Syndrome Menkes disease(kinky hair syndrome) Hemophilia Color blindness Inherited diabetes (Type 1)

ALD (Adrenoleukodystrophy) A deadly genetic disease that is a result of fatty acid buildup caused by the enzymes not functioning properly Causes damage to the nerves, resulting in neurological issues and, later, death

Hypertrichosis An abnormal amount of hair growth over the body Informally called werewolf syndrome, because the appearance is similar to the mythical werewolf

Hypertrichosis

Are you colorblind?

Color Blindness Having a decreased ability to see some colors or differences in colors Red-Green is most common

Think how difficult some things would be if you have colorblindness

What about this…. Imagine life without being able to see true colors!

Menke’s Disease (Kinky Hair Syndrome) Rapid deterioration of the nervous system. Weak muscle tone, sagging facial features, seizures, developmental delay, and intellectual disability caused by enzymes not functioning Children with Menkes syndrome typically begin to develop symptoms during infancy and often do not live past age 6 

Menke’s Disease

Hemophilia The “Royal Blood Disease” impairs the body's ability to make blood clots Clots are needed to stop bleeding This results in people bleeding longer after an injury and an increased risk of bleeding inside joints or the brain

Hemophilia Remember the Royal Family?

Tay-Sachs Tay-Sachs disease is a rare inherited disorder that progressively destroys nerve cells (neurons) in the brain and spine Enzymes are the culprit AGAIN! Paralysis of the nerves cause eventual death

Tay-Sachs Tay Sachs

Duchene Muscular Dystrophy Duchenne muscular dystrophy (DMD) is a genetic disorder characterized by progressive muscle degeneration and weakness Until relatively recently, boys with DMD usually did not survive much beyond their teen years Advances in cardiac and respiratory care means that survival into the early 30s is becoming more common

Duchenne Muscular Dystrophy

PKU (PhenylKetonUrea) Decreased metabolism of the amino acid phenylalanine Enzymes can’t break it down! Untreated PKU can lead to intellectual disability, seizures and death 

PKU

Cystic Fibrosis (CF) A genetic disorder that affects mostly the lungs, but also the pancreas, liver, kidneys, and intestine Cystic Fibrosis The enzymes required to break down mucous are not functioning, so the mucous collects and clogs…

SCID (Severe combined immunodeficiency) Do you know “David, the Boy in the Bubble”, who was born without a working immune system?

SCID What happens when your immune system doesn’t work??? https://www.nytimes.com/video/us/100000004077071/the-boy-in-the-bubble.html

Albinism Albinism is an inherited genetic condition that reduces the amount of melanin pigment formed in the skin, hair and/or eyes. Albinism occurs in all racial and ethnic groups throughout the world. As well as other species!

Albino Animals

Different degrees of Albinism…

Y linked Hairy ears