Genetics Honors Project: Modes of Inheritance
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Genetics Honors Project: Modes of Inheritance

In this video we will talk about the different
modes of inheritance including autosomal dominant, x-linked recessive, x-linked dominant, y-linked,
cytoplasmic inheritance also known as mitochondrial inheritance, and autosomal recessive. Steven has Marfan syndrome. Marfan syndrome is an autosomal dominant disorder
characterized by long limbs, such as fingers, toes, arms, and legs. Additionally, people with Marfan syndrome
may have displaced eye lenses or heart valve problems. Because it is a dominant trait, one of his
parents must have it – this is why dominant traits do not skip generations. In his pedigree, we can see that his mother
has had kids with two different men. She did not know which father was Steven’s
father, but we do because her first husband had the trait so he must be the father. Steven married someone without the syndrome
and had kids who are also unaffected. This indicates that he was heterozygous for
the disorder because his wife has to be homozygous recessive to be unaffected, and so do his
kids. This is John. John has Red-Green colorblindness. His father does not carry the gene for this,
which is indicated by him not expressing the trait. For X-linked traits, males either have the
trait or not; they cannot be carriers since they only have one X chromosome. Because Red-Green color blindness is recessive,
his father is dominant for having normal vision. This means that he only passes down the genetic
material on his Y chromosome to his sons, while passing down the genes on his X chromosome
to all of his daughters. All of his daughters are unaffected because
he passed down the dominant gene to them. However, John’s mother does carry the gene. Unfortunately for John, his mother passed
down this trait to him since it was on one of her X-chromosomes. Luckily for John’s sisters, they all got
their father’s dominant gene. Whether they are carriers or not is unknown. John’s wife is a carrier but does not have
the trait, so she passed down her dominant trait to their sons while passing the recessive
gene to their daughter. In this pedigree, we can see that recessive
traits can typically skip generations. Andrea is affected by X-linked hypophosphatemia. X-linked hypophosphatemia is characterized
by bone deformities due to insufficient levels of phosphate in the blood. Andrea marries a non-carrier and they have
four kids together, two boys and two girls. Out of her four children, one of her boys
and one of her girls inherited this syndrome. Because not all of her children inherited
the disorder, we know she must be heterozygous. Since the gene is located on one of Andrea’s
X-chromosomes, that means she has a 50% chance of passing on that specific X-chromosome. She indeed did, causing one of her sons and
one of her daughters, to be affected with X-linked hypophosphatemia. Billy is affected with Y chromosome infertility;
however, he has mild oligospermia, which means that he still produces sperm but it is much
less than the normal male. Due to his oligospermia, it was very difficult
for him to conceive children and he had to resort to assisted reproductive technologies
to help him conceive with his wife Alexis. Billy and Alexis had 5 kids, three of which
are males who were all also affected with oligospermia. This is due to the condition being a Y-linked
disorder, meaning every male Billy conceived would have been affected with the disorder
since he passes his Y chromosome to all of his sons. Billy’s sons will also have to seek further
reproductive assistance if they want to conceive. Deborah carries some mutated mtDNA. Unbeknownst to her, these mutations can cause
Leber Hereditary Optic Neuropathy. However, she does not express any symptoms
of this. When she got pregnant, she unknowingly passed
this genetic material to her kid. Only Deborah, and not her husband, can pass
this genetic material down because only the egg donates mitochondria to the fetus, not
the sperm. Although only the mother can pass it down,
both males and females can inherit any associated disorders or traits. This transmission of the mitochondrial genes
caused some of her children to inherit Leber’s hereditary optic neuropathy, a degenerative
optic disorder causing vision loss in young-adulthood. Out of Deborah’s 6 children, 2 inherited
the disorder due to it being a cytoplasmic inheritance.Cystic fibrosis is an autosomal
recessive disorder. This means a person must have two copies of
the recessive allele in order to have cystic fibrosis. In this pedigree, you can see that the mother,
Susan, has the disorder, indicated by little h little h. Out of her five kids, luckily no one got the
disorder! However, because their mother was homozygous
recessive, they all have to be carriers for it, giving them a 100% chance of being a carrier. Susan’s oldest daughter married someone
who is homozygous recessive and their son ended up with the disorder. The rest of Susan’s kids married people
who were homozygous dominant for being healthy. All of these people passed down their dominant
alleles, so none of the kids ended up with the disease. If Susan’s kids marry someone who is a carrier,
then their kids have a 25% chance of getting the disorder and a 50% chance of being a carrier. And this has been a presentation on the various
modes of inheritance one may encounter when learning genetics.

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