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

Fig. 12.5, p umbilical cord (lifeline between the embryo and the mother’s tissues) amnion (a protective, fluid- filled sac surrounding and cushioning the embryo) 10 weeks Y chromosome present Y chromosome absent 7 weeks birth approaching penisvaginal opening appearance of structures that will give rise to external genitalia appearance of “uncommitted” duct system of embryo at 7 weeks Y chromosome present Y chromosome absent penis testis ovary uterus vagina testesovaries

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 17 Hydroxyprogesterone Testosterone Dihydrotestosterone Enzyme 1 Enzyme 2 Enzyme 3 (5  reductase) SRY turns on enzymes (internal male gentilia) ( 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)