Lecture 9 Genetics Gregor Mendels Discoveries Second The

Lecture 9: Genetics Gregor Mendel’s Discoveries

Second: The law of independent assortment Mendel’s experiments that followed the inheritance of flower color or other characteristics focused on only a single characteristic via monohybrid cross ﺍﻟﺘﺰﺍﻭﺝ ﺃﺤﺎﺩﻱ ﺍﻟﺼﻔﺔ Mendel also analyzed the inheritance pattern of two traits at the same time via a dihybrid cross ﺍﻟﺘﺰﺍﻭﺝ ﺛﻨﺎﺋﻲ ﺍﻟﺼﻔﺔ. For example, he examined plants that differed in both the shape and color of their peas. He crossed homozygous plants that produced yellow, round seeds (YYRR) with plants that produced green, wrinkled seeds (yyrr). He founds that: Ø Yellow seeds (Y) was dominant to green seeds (y). Ø Round seeds (R) was dominant to wrinkled seeds (r)

Dihybrid cross ﺍﻟﺘﺰﺍﻭﺝ ﺛﻨﺎﺋﻲ ﺍﻟﺼﻔﺔ It is a mating ﺗﺰﺍﻭﺝ between two parent plants different in two characteristics. The two pairs of alleles segregate independently of each other. When the F 1 plants were selffertilized, they produced an F 2 generation of plants that had all four phenotypic ratios (9: 3: 3: 1) of the two seed characteristics: v 9 plants with yellow, round seeds. v 3 plants with green, round seeds. v 3 plants with yellow, wrinkled seeds. v 1 plants green, wrinkled seeds.

Genetic disorders in human A) Recessive genetic disorders ﻻﺕ ﺍﻟﻮﺭﺍﺛﻴﺔ ﺍﻟﻤﺘﻨﺤﻴﺔ ﻼ ﺍﻻﻋﺘ Thousands of genetic disorders ﻻﺕ ﻭﺭﺍﺛﻴﺔ ﺍﻋﺘ ﻼ , including disabling ﺍﻹﻋﺎﻗﺔ or deadly genetic diseases ﺍﻷﻤﺮﺍﺽ ﺍﻟﻮﺭﺍﺛﻴﺔ ﺍﻟﻣﻴﺘﺔ , are inherited as simple recessive traits ﺻﻔﺎﺕ ﺗﻨﺤﻴﺔ. Heterozygotes have a normal phenotype because one “normal” allele produces enough of the required factors (for normal trait). Thus, individuals who lack the disorder are either homozygous dominant or heterozygous. Heterozygous member may have no clear phenotypic effects, but is a carrier who may transmit a recessive allele to their offspring. Two carriers have a 1/4 (25%) chance of having a child with the disorder, 1/2 (50%) chance of a carrier, and 1/4 (25%) free. Recessive genetic disorders include albinism ﺍﻟﺒﻬﺎﻕ , cystic fibrosis ﺍﻟﺘﻠﻴﻒ ﺍﻟﻜﻴﺴﻲ , Tay-Sachs disease ﻣﺮﺽ ﺗﺎﻱ ﺳﺎﻛﺲ and sickle cell anemia ﺍﻷﻨﻴﻤﻴﺎﺀ ﺍﻟﻤﺠﻠﻴﺔ

1 - Albinism ﺍﻟﺒﻬﺎﻕ X-linked recessive ﻣﺘﻨﺤﻲ ﻣﺮﺗﺒﻂ ﺑﻜﺮﻭﻣﻮﺳﻮﻡ ﺍﻛﺲ Absence of melanin pigment ﺻﺒﻐﺔ ﺍﻟﻤﻴﻼﻧﻴﻦ in the hair, skin and eyes. Albinism results from inheritance of recessive gene alleles. Albinism is caused by an alteration of the gene that makes the melanin pigment Albinism is associated with vision ﺍﻟﺮﺅﻴﺔ problems and skin cancer ﺳﺮﻃﺎﻥ ﺍﻟﺠﻠﺪ. 2 - Cystic Fibrosis ﺍﻟﺘﻠﻴﻒ ﺍﻟﻜﻴﺴﻲ Autosomal recessive ﻣﺘﻨﺤﻲ ﺟﺴﺪﻱ , gene located in chromosome 7 It is caused by the presence of mutations in both copies of the gene for the protein Cystic Fibrosis Transmembrane Conductance Regulator (CFTR). CFTR gene controls chloride ion movement in and out of the cell. It affects mostly the lungs but also the pancreas, liver and kidneys. Without treatment, affected children die before five, but with treatment

Cystic fibrosis is inherited in the autosomal recessive pattern

3 - Tay-Sachs disease ﻣﺮﺽ ﺗﺎﻱ ﺳﺎﻛﺲ ﺃﻮ ﺍﻟﺒﻠﻪ ﺍﻟﻤﻤﻴﺖ Autosomal recessive ﻣﺘﻨﺤﻲ ﺟﺴﺪﻱ Tay–Sachs results from mutations in the HEXA gene on chromosome 15 Mutation of HEXA gene leads to accumulate lipids in the brain's nerve cells leading to the death of the cells. The symptoms ﺍﻷﻌﺮﺍﺽ begin with seizures ﻧﻮﺑﺔ ﻋﺼﺒﻴﺔ , blindness ﻋﻤﻰ , and mental and physical disabilities ﺇﻋﺎﻗﺔ ﻋﻘﻠﻴﺔ ﻭﺟﺴﺪﻳﺔ six months after birth and usually results in death by the age of four. 4 - Sickle-cell anemia ﺍﻷﻨﻴﻤﻴﺎﺀ ﺍﻟﻤﺠﻠﻴﺔ Autosomal recessive ﻣﺘﻨﺤﻲ ﺟﺴﺪﻱ Sickle cell anemia results from mutations in the HBB gene ﻫﻴﻤﻮﺟﻠﻮﺑﻴﻦ ﺑﻴﺘﺎ on chromosome 11 It is caused by the substitution ﺍﺳﺘﺒﺪﺍﻝ of a single amino acid in hemoglobin. People with sickle-cell anemia have abnormal hemoglobin in their red blood cells. Hemoglobin is a protein that carries oxygen throughout the body. Doctors can use regular blood transfusions ﻧﻘﻞ ﺍﻟﺪﻡ to prevent brain damage and new drugs to prevent or treat other problems.

B) Dominant genetic disorders ﻻﺕ ﺍﻟﻮﺭﺍﺛﻴﺔ ﺍﻟﺴﺎﺋﺪﺓ ﻼ ﺍﻻﻋﺘ 1 - Achondroplasia ﺍﻟﻘﺰﻣﻴﺔ Autosomal dominant ﺳﺎﺋﺪ ﺟﺴﺪﻱ Achondroplasia is caused by a mutation in fibroblast growth factor receptor 3 (FGFR 3) gene on chromosome 4 People with achondroplasia have short stature ﻗﺼﺮ ﺍﻟﻘﺎﻣﺔ , with an average adult height of 131 centimeters for males and 123 centimeters for females. Heterozygous individuals have the dwarf ﻗﺰﻡ phenotype. Lethal dominant alleles ﺍﻷﻠﻴﻼﺕ ﺍﻟﺴﺎﺋﺪﺓ ﺍﻟﻤﻤﻴﺘﺔ are much less common ﺃﻘﻞ ﺷﻴﻮﻋ than lethal recessives, because if a lethal dominant kills an offspring before it can mature and reproduce, the allele will not be passed on future generations ﺃﺠﻴﺎﻝ ﺍﻟﻤﺴﺘﻘﺒﻞ.

2 - Huntington’s disease ﻣﺮﺽ ﻫﻨﺘﻨﻐﺘﻮﻥ Autosomal dominant ﺳﺎﺋﺪ ﺟﺴﺪﻱ Huntington’s disease is caused by a mutation in HD gene is located in chromosome 4 The dominant lethal allele has no obvious phenotypic effect until an individual is about 35 to 45 years old. Huntington's disease is an inherited condition that damages nerve cells in the brain. Huntington's disease results in an losing of both mental and physical control.

Summary of the human genetic disorders Dominant trait ﺍﻟﺼﻔﺔ ﺍﻟﺴﺎﺋﺪﺓ : Describes a trait that is expressed when only one copy of the allele is present in the genotype. Recessive trait ﺍﻟﺼﻔﺔ ﺍﻟﻤﺘﻨﺤﻴﺔ : Describes a trait that is masked by the dominant trait and is only expressed in the homozygous condition. Autosome ﺍﻟﻜﺮﻭﻣﻮﺳﻮﻡ ﺍﻟﺠﺴﺪﻱ : Any chromosome that is not a sex chromosome. Humans have 22 pairs of autosomes and one pair of sex chromosomes (the X and Y). Genetic disorders caused by genes on autosomes are called autosomal disorders. q Some genetic disorders are autosomal dominant ﺳﺎﺋﺪ ﺟﺴﺪﻱ v An individual with AA has the disorder v An individual with Aa has the disorder v An individual with aa does not have disorder q Other genetic disorders are autosomal recessive ﻣﺘﻨﺤﻲ ﺟﺴﺪﻱ v An individual with AA does not have disorder v An individual with Aa does not have disorder, but is a carrier ﺣﺎﻣﻞ v An individual with aa has the disorder