Transcript Human Genetics

Human Genetics
Disorders and abnormalities
Chromosomes
• Chromosomes can be divided into two different
groups: autosomes and sex chromosomes
– Autosomes are the 22 chromosomes other than the
sex chromosomes. They each have homologs which
code for the same genes
– Sex chromosomes are the “X” and “Y”
• XX = female
• XY = male (homologous pair code for different genes)
The Y chromosome
• The Y chromosome determines sex.
– The “sex determining region on the Y
chromosome” (SRY) determines the sex of the
individual.
• If you have the SRY- you are male.
• Females are said to be the default sex. That is, all
zygotes are destined to be female unless the SRY
gene kicks in.
– If there is no SRY gene (XX) or if the SRY gene dosen’t
work (XY) the zygote will be a phenotypic female
appearance of structures
that will give rise to
external genitalia
appearance of
“uncommitted” duct system
of embryo at 7 weeks
umbilical cord (lifeline
between the embryo
and the mother’s tissues)
7 weeks
Y chromosome
present
10 weeks
penis
Y chromosome
absent
10 weeks
Y chromosome
present
Y chromosome
absent
testes
ovaries
amnion (a protective, fluidfilled sac surrounding and
cushioning the embryo)
vaginal
opening
ovary
penis
birth approaching
birth approaching
uterus
vagina
testis
Fig. 12.5, p. 196-7
Intersex
• What is it?
• Intersex is a state where a newborn’s sex
orgrans has anatomic characteristics of both
sexes, making it impossible to identify the
sex of the baby from its outward
appearance. Sometimes, the genetic sex (as
indicated by chromosomes) may not match
the appearance of the sex organs.
Intersex
• Who gets it?
• Intersex affects one in every 2,000 births.
– U.S. population = 295,734,134
– 147,867 people in the united states.
• What causes it?
• Intersex may be caused by any abnormality in
chromosomes or sex hormones, or in the unborn
baby's response to the hormones. The condition
can also be caused by congenital adrenal
hyperplasia, a disease that blocks the infant’s
metabolism and can cause a range of symptoms,
including abnormal sex organs.
Cholesterol
Enzyme 1
17 Hydroxyprogesterone
SRY turns on
enzymes
Enzyme 2
Testosterone
(internal male gentilia)
Enzyme 3
(5 a reductase)
Dihydrotestosterone (external male gentilia)
The Family:
A Proclamation to the World
• We, the First Presidency and the Council of the Twelve
Apostles of The Church of Jesus Christ of Latter-day
Saints, solemnly proclaim that …
All human beings—male and female—are created in the
image of God. Each is a beloved spirit son or daughter of
heavenly parents, and, as such, each has a divine nature
and destiny. Gender is an essential characteristic of
individual premortal, mortal, and eternal identity and
purpose.
Genetic Disposition
of Homosexuality
• KING: ... But as the mores have changed - for example, I know that the Church is
opposed to gay marriage.
• HINCKLEY: Yes.
• KING: Do you have an alternative? Do you like the idea of civil unions?
• HINCKLEY: Well, we're not anti-gay. We are pro-family. Let me put it that way.
And we love these people and try to work with them and help them. We know
they have a problem. We want to help them solve that problem.
• KING: A problem they caused, or they were born with?
• HINCKLEY: I don't know. I'm not an expert on these things. I don't pretend to be
an expert on these things. The fact is, they have a problem.
Human Genetics
Abnormalities vs. Disorders
• Genetic disorder: A term used to describe a
condition that causes medical problems.
– Example Cystic fibrosis
• Genetic abnormalities are characteristics
that deviate from the average and is not life
threatening
– Extra fingers and toes
Inheritance of disorders and
abnormalities
• Genetic disorders and abnormalities are
inherited as alleles
• Alleles for abnormalities and disorders may
either be dominant or recessive to alleles
carrying normal traits.
• Alleles for abnormalities and disorders may
either be carried on autosomes or on one of
the sex chromosomes
Patterns of Inheirtance
• Genetic diseases display different patterens
of inheritance depending on whether the
alleles are on autosomal chromosomes or
sex chromosomes.
• They also show different patterns of
inheirtance depending on whether they are
dominant or recessive
Autosomal dominant disorders
• The allele that carries the disorder is found
on one of the autosomes
• The alleles that carry the genetic disease are
dominant over the normal healthy alleles.
• The genotypes “AA” and “Aa” would both
express the disorder.
• “aa” individuals are normal
Question:
• One parent is heterozygous for an
autosomal dominant disorder and the other
is homozygous recessive. What are the
chance of these parents having a child with
the disease?
Autosomal recessive
• The allele that carries the disorder is found on one
of the autosomes
• The alleles that carry the genetic disease are
recessive to the normal healthy alleles.
• The genotype “aa” would express the disorder.
• Individuals who have the genotype “Aa” are
carriers for the disease
• “AA” individuals are normal
Question
• Two parents each are carriers for an
autosomal recessive disorder. What is the
probability of this couple having a child
with this disorder?
X-Linked recessive disorder
• The allele that carries the disorder is found on the
X chromosome.
• The alleles that carry the genetic disease are
recessive to the normal healthy alleles.
• The genotype “xx” would express the disorder.
• Individuals who have the genotype “Xx” are
carriers for the disease
• “XX” individuals are normal
• Phenotype shows up far more often in males than
females
• Red green colored blindness and Hemophilia are
examples of x-linked traits.
Question
• If a father is colored blind what is the
chances that his son will be?
X linked dominant
• Pattern is similar to X linked recessive
except the trait is expressed in heterozygous
females
• Mother transmit to half of her offspring
regardless of the sex.
Question
• Can a son inherit an X linked dominant trait
from his father?
Aneuploidy
• Nondisjunction is a term used to describe
sister chromotids that were not separated
during meiosis.
• Nondisjunction causes an abnormal number
of chromosomes or aneuploidy in the cells.
• Ther are two different types of aneuploidy
– Monosomy (2n-1)
– Trisomy (2n+1)
Diseases caused by aneuploidy
• Down syndrome = trisomy 21
• Turner syndrome = monosomy (XO)
• Klienfelter = Trysomy (XYY)