BIOLOGY UNDERSTANDING HUMAN GENETICS Chromosomes Every human cell

BIOLOGY UNDERSTANDING HUMAN GENETICS

Chromosomes Every human cell has 46 chromosomes (23 pairs of chromosomes) A karyotype is a picture of the 23 pairs of chromosomes.

EXAMPLES OF KARYOTYPES Autosomes are the first 22 pairs of chromosomes (#1 -#22) Sex Chromosomes determine the sex and are pair #23 Female (XX) XX-female XY-male Male (XY) • Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http: //www. biologycorner. com/bio 1/celldivision-chromosomes. html

Pedigree Charts-shows genetic history of a family over many generations Generation III • Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http: //www. biologycorner. com/bio 2/humangenetics. html

Symbols in a Pedigree Chart Female • Male Sick Female Sick Male

Married Couple horizontal line connects a married couple • Siblings

Shaded: individual has the trait Not shaded: does not have the trait • Half-shaded: carries the trait (heterozygous)

Pedigree Chart of a Dominant Trait Huntingtons disease is a dominant disease that damages the nervous system One dominant allele means you get the disease HH (homozygous) and Hh (heterozygous) will have the disease hh (homozygous) will not have the disease One parent has to have it to pass on to child What is the genotype of the father? What is the genotype of the son?

Pedigree Chart of a Dominant Trait The father does not have the dominant disease so he must have 2 recessive alleles; his genotype is hh The son has the dominant disease so he has to have at least one dominant allele. Is his genotype HH or Hh? One allele came from his father so his genotype is Hh.

Pedigree Chart of a Dominant Trait What are the chances that future offspring of this couple will have this dominant disease? Use the genotypes of the parents to draw a punnett square. hh HH Hh

Pedigree Chart of a Dominant Trait H hh H HH h Hh Hh Hh All of the offspring have the dominant allele so 100% of their future children will have this dominant disease.

Pedigree Chart of a Recessive Trait. Cystic fibrosis is a recessive disease causing digestive problems HH (homozygous) and Hh (heterozygous) will NOT have the disease hh (homozygous) will have the disease Must inherit recessive allele from each parent to have the disease What is the genotype of the father? What is the genotype of the daughter?

Pedigree Chart of a Recessive Trait The dad does not have this recessive disease so his genotype is either CC or Cc. Since he passed on one recessive allele to his daughter, his genotype is Cc. She must have 2 recessive alleles to have this disease. Her genotype is cc.

Pedigree Chart of a Recessive Trait What are the chances that future offspring of this couple will have this recessive disease? Use the genotypes of the parents to draw a punnett square. Cc Cc cc

Pedigree Chart of a Recessive Trait C c C CC Cc c Cc cc Only 1 out of 4 offspring have the recessive disease (cc). There is a 25% chance of future offspring having the disease. Cc Cc cc

Sex-Linked Traits (X-linked) Sex-linked genes are located on the sex chromosomes (23 rd pair) and deal with the X and Y chromosome A female is XX; a male is XY Sex-linked genes are shown as superscripts on the X chromosome

Sex-Linked Traits in females If a disorder is caused by a recessive gene, a female’s genotype could be XBXB or XBXb and she will not have the disorder. The XBXb female would be a carrier. A female with a sex linked disorder would be written as Xb. Xb because she must have both recessive alleles.

Sex-Linked Traits in males The Y chromosome does NOT carry a gene. A male without the recessive sex-linked disorder would be XBY. A male with the sex-linked disorder would be Xb. Y. Sex-linked disorders are more common in males because males only need 1 copy of the recessive allele since they have only 1 X chromosome. Females must have 2 copies of the recessive allele since they have 2 X chromosomes. Common sex-linked disorders include color blindness and hemophilia (a bleeding disorder)

Sex-linked pedigree for color blindness What is this male’s genotype? Colorblindness is a recessive sex-linked disorder This is a male so his sex chromosome is XY The square is shaded so this male is colorblind His genotype is Xb. Y (Remember, there are no superscripts on the Y chromosome) • Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http: //www. biologycorner. com/bio 4/notes/inheritance 3. html

Sex-linked pedigree for color blindness What is this male’s genotype? This is a male so his sex chromosome is XY The square is not shaded so this male has normal vision His genotype is XBY • Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http: //www. biologycorner. com/bio 4/notes/inheritance 3. html

Sex-linked pedigree for color blindness What is this female’s genotype? This is a female so her sex chromosome is XX This female is not colorblind so her genotype is either XBXB or XBXb Her son is shaded so he is colorblind (Xb. Y) and inherited the Y chromosome from his father and the Xb chromosome from his mother. The mother has to have a Xb in her genotype Her genotype is XBXb • Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http: //www. biologycorner. com/bio 4/notes/inheritance 3. html

Practice What percentages can be expected in the offspring of a cross between a female carrier for color blindness and a male with a normal color vision? Show your work with a punnett square.

Practice What percentages can be expected in the offspring of a cross between a female carrier for color blindness and a male with a normal color vision? Color blindness is a recessive trait attached to the X chromosome. A female carrier means heterozygous. female carrier XBXb male with normal vision XBY XB 25% normal females XB XBXB Xb XBXb 25% carrier females 25% normal males Y XBY Xb. Y 25% colorblind males

Karyotypes are used to determine if an offspring has the right number of chromosomes (46 in humans) Down Syndrome 47 chromosomes because there are 3 copies of chromosome #21 Causes mental retardation 3 copies of #21 • Muskopf, Shannan. Online Images. The Biology Corner. 8 May 2007. http: //www. biologycorner. com/bio 1/celldivision-chromosomes. html

Diagnosis of Chromosomal Abnormality • Amniocentesis-during pregnancy, a small amount of fluid from the sac surrounding the embryo is used to make a karyotype to determine if the fetus has the correct number of chromosomes

Amniocentesis

What is a karyotype? Karyotype is a term in genetics. It refers to the complement of chromosomes either at the species level, or of indivduals. The normal human karyotype comprises 23 pairs of chromosomes, making 46 in total. In humans - and indeed in mammals, the final pair varies between males (XY) and females (XX)

Human Karyotype

Normal Male Karyotype

Normal Female Karyotype

Cystic Fibrosis Is inherited disease of the secretory glands. ( sweat and mucus) Inherited means the disease is passed from parents to children through genes. May cause respiratory failure May affect : pancreas liver intestines sexual organs sinuses

Cystic Fibrosis Mucus is a substance made by tissue that line some organs in the body cavities (lungs and nose) Buildup of mucus can cause bacteria to grow and cause infection. People with CF will have a salty sweat.

Huntington Disease Huntington´s disease (HD) is an autosomal dominant neurodegenerative disease for which no cure is currently available. Huntington's disease (HD) results from genetically programmed degeneration of brain cells, called neurons, in certain areas of the brain. This degeneration causes uncontrolled movements, loss of intellectual faculties, and emotional disturbance.

Huntington Disease Huntington's disease is inherited in an autosomal dominant fashion. The probability of each offspring inheriting an affected gene is 50%. Inheritance is independent of gender, and the phenotype does not skip generations.

Tay Sachs Tay-Sachs disease is caused by a defective gene on chromosome 15. When both parents carry the defective Tay-Sachs gene, a child has a 25% chance of developing the disease. The child must receive two copies of the defective gene -- one from each parent - in order to become sick Most common Eastern European Jews

Tay Sachs Infants with Tay-Sachs disease appear to develop normally for the first few months of life. As nerve cells become distended with fatty material, a relentless deterioration of mental and physical abilities occurs. The child becomes blind, deaf, and unable to swallow . Other neurological symptoms include dementia, seizures, and an increased startle reflex to noise.

Cri du Chat Cri du chat syndrome is a group of symptoms that result from missing a piece of chromosome number 5. The syndrome’s name is based on the infant’s cry, which is high-pitched and sounds like a cat. 1/20, 000 individuals Less 20%

Cri du Chat

Turner Syndrome

Klinefelter Syndrome

Edwards Syndrome

Down Syndrome

Patau Syndrome

This the you need to known for the Quiz Tay Sachs Huntington Disease Cystic Fibrosis Down syndrome Patau Syndrome Edwards Syndrome Turner Syndrome Klinefelter Syndrome Cri du Chat Karyotype