Complex Patterns of Inheritance Chromosomes and Human Heredity

Advanced Genetics Fundamental genetics. Genetics Disorders Dominant/Recessive traits Incomplete Dominance Codominance Sex-Linked traits Genetics Disorders Recessive allele disorders Dominant allele disorders Codominant allele disorders Sex-linked disorders Chromosomal disorders

Genetic disorders Most genetic disorders are caused by a single allele. The allele could be either dominant or recessive. The alleles could be carried on either autosomes or sex chromosomes.

Recessive Allele Disorder A genetic disorder caused by a recessive allele does not show in a heterozygous individual. The individual can still pass the trait on to his/her child. Therefore this person is considered a carrier. AA = Normal Aa = Carrier aa = Affected

Recessive genetic disorders Tay-Sachs Disease Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration. Causes blindness, seizures and death in the early years of life

Recessive genetic disorders Cystic Fibrosis Affects the mucus- producing glands, digestive enzymes, and sweat glands Causes a mucous build up in the lungs

Dominant genetic disorders Huntington’s Disease Causes a breakdown of the nervous tissue Has an onset of approximately 20 years of age. Achondroplasia Genetic condition that causes small body size and limbs that are comparatively short.

Codominant disorders Sickle-Cell Disease Normal red blood cell Sickle-Cell Disease Causes the red blood cells to become sickle shaped. Could cause severe pain, cramping, and blood clotting. Sickle cells

Sex-linked disorders Colorblindness Hemophilia The person cannot distinguish between two colors, commonly red and green. Hemophilia Causes an inability to clot blood.

Chromosomal disorders Down’s Syndrome Caused by an extra 21st chromosome (Trisomy 21) Turner’s Syndrome Caused by a missing X chromosome (Monosomy X) Klienfelter’s Syndrome Caused by an extra X chromosome (XXY)

Karyotypes Genetic testing can be used to develop a karyotype A karyotype is a lining up of all the homologous chromosomes from a cell Images of chromosomes are stained during metaphase It is used to look for major chromosome abnormalities: Size of each chromosome Number of chromosomes * What is the sex of this child? * Are there any abnormalities?

Karyotypes Turner’s Syndrome Down’s Syndrome What is the sex of this child? Are there any abnormalities? What is the sex of this child? Are there any abnormalities? Turner’s Syndrome Down’s Syndrome

Chromosomal Abnormalities Some of the more serious genetic diseases are caused by a missing or extra chromosome. This is due to complications during meiosis. So what would happen if the sister chromatids didn’t separate? * One cell would be missing a chromosome, and the other cell would have two chromosomes. Remember meiosis…

nondisjunction Don’t Separate Nondisjunction – when chromosomes don’t separate during meiosis. This happens primarily during Meiosis II if the centromeres don’t break. Don’t Separate

Fertilization Results in Monosomy – Having one chromosome instead of a pair. Could result in Turner’s Syndrome.

Fertilization Results in Trisomy – Having 3 chromosomes instead of a pair Could result in Down Syndrome

Basic Patterns of inheritance Punnett squares allow us to determine the phenotypes and genotypes of future offspring. However, this method only works if we know the particular genotypes we’re working with. So how do we track a specific trait through a family, thus allowing us to use the punnett square method? Pedigree - A diagram that traces the inheritance of a particular trait through several generations

Pedigrees Identical Twins Fraternal Twins Inferring Genotypes - Knowing physical traits can determine what genes an individual is most likely to have. Predicting Disorders - Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and ascertain genotypes.

The Royal Family pedigree * Tracking a trait using a Pedigree