Life Science I 83 101 201 Dr Ekaterina

Life Science I 83. 101. 201 Dr. Ekaterina (Kate) Vorotnikova Office: 413 b E-mail: Ekaterina_Vorotnikova@uml. edu Lecture 20 Multiple alleles, ABO blood groups. Sex chromosomes and sex-linked genes (page 167; 174 -177. Questions: page 179 # 2 -4; 6 )

Incomplete dominance results in intermediate phenotypes Incomplete dominance – Neither allele is dominant over the other – Expression of both alleles is observed as an intermediate phenotype in the heterozygous individual Copyright © 2009 Pearson Education, Inc.

Incomplete dominance in human hypercholesterolemia Genotypes: HH Homozygous for ability to make LDL receptors Hh Heterozygous hh Homozygous for inability to make LDL receptors Phenotypes: LDL receptor Cell Normal Mild disease Severe disease

Pleiotropy One gene influencing many phenotypic characteristics. The gene for sickle cell disease: • Affects the type of hemoglobin produced; • Affects the shape of RBC; • Causes anemia; • Causes organ damage; • Is related to susceptibility to malaria. Sickle-cell disease, multiple effect of a single human gene

Many genes have more than two alleles in the population Multiple alleles • More than two alleles are found in the population • A diploid individual can carry any two of these alleles • The ABO blood group has three alleles, leading to four phenotypes: type A, type B, type AB, and type O blood • ABO blood types are inherited through genes on chromosome 9 Copyright © 2009 Pearson Education, Inc.

Codominance Neither allele is dominant over the other. Expression of both alleles is observed as a distinct phenotype in the heterozygous individual. Observed for type AB blood

Genetic Inheritance Patterns ABO blood types are inherited through genes on chromosome 9, and they do not change as a result of environmental influences during life. An individual's ABO type is determined by the inheritance of 1 of 3 alleles (A, B, or O) from each parent. The possible outcomes are shown below: Parent Alleles IA IB i I AI A (A) I AI B (AB) I BI B (B) I Ai (A) I Bi (B) ii (O) The possible ABO alleles for one parent are in the top row and the alleles of the other are in the left column. Offspring genotypes are shown in black. Phenotypes are red.

An international team of researchers led by Henrick Clausen of the University of Copenhagen, Denmark have discovered a bacterial enzyme that can convert red blood cells of types A, B, and AB into O by stripping away their identifying surface antigens. This has the potential for dramatically improving the safety of blood transfusions. Clinical trials of this technique are now underway. ("Bacterial Glycosidases for the Production of Universal Red Blood Cells", published online in Nature Biotechnology, April 1, 2007).

SEX CHROMOSOMES AND SEX-LINKED GENES Copyright © 2009 Pearson Education, Inc.

Chromosomes determine sex in many species X-Y system in mammals, fruit flies • XX = female; XY = male X-O system in grasshoppers and roaches • XX = female; XO = male Z-W in system in birds, butterflies, and some fishes • ZW = female, ZZ = male Chromosome number in ants and bees • Diploid = female; haploid = male Copyright © 2009 Pearson Education, Inc.

X Y

The X-Y system (female) (male) 44 + XY 22 + X Parents’ diploid cells 44 + XX 22 + Y Sperm 22 + X 44 + XY Offspring (diploid) Egg

The X-O system 22 + XX 22 + X Grasshoppers, roaches and some other insects have an X-O system, in which O stands for the absence of a sex chromosome

The Z - W system 76 + ZW 76 + ZZ Eggs determine sex in fishes, butterflies and birds. Sex-linked traits affect female birds to a greater extent than males. A female would need to inherit only one copy of a Z-linked recessive allele to show a specific trait, while a male would need to inherit two copies. Bird populations can become endangered if the numbers of females decline due to harmful Z-linked traits.

32 Sex determination by chromosome number: bees, ants 16

Sex-linked genes exhibit a unique pattern of inheritance Fruit fly eye color, a sex-linked characteristic R is dominant, wild-type, red-eye allele; r is recessive, white-eye allele. They are carried on the X chromosome.

Sex-linked genes can be located on either of the sex chromosomes Reciprocal crosses show different results Red-eyed female whiteeyed male = red-eyed females and red-eyed males

X-linked genes are passed from mother to son and mother to daughter X-linked genes are passed from father to daughter Y-linked genes are passed from father to son Red-eyed female redeyed male = red-eyed females, red-eyed males and white-eyed males

Red-eyed female red-eyed male = red-eyed females, white -eyed females, red-eyed males and white-eyed males

CONNECTION: Sex-linked disorders in humans affect mostly males Males express X-linked disorders such as the following when recessive alleles are present in one copy • Hemophilia • Colorblindness • Duchenne muscular dystrophy Copyright © 2009 Pearson Education, Inc.

DNA analysis has revealed the identity of the "cursed blood" disorder that afflicted the British Royal Family in the 19 th and early 20 th centuries. Queen Victoria's great grandson Crown Prince Alexis was a hemophiliac The mutation was transmitted from Russian Empress Alexandra to her son Crown Prince Alexis. The analysis of the remains of Victoria's Russian descendants helped identify the exact form of hemophilia. Modern analytical techniques allowed the scientists to amplify the very degraded DNA. They discovered a mutation in a gene on the X chromosome that codes for the production of Factor IX, a substance that causes blood to clot. This genetic mutation is the cause of hemophilia B.

Extra credit question. A)Alexis did not die from hemophilia. At the age of fourteen he was executed with the rest of the family. His four oldest sisters were also young and didn’t have children, so we don’t know whether any of them was a carrier. But we can make an estimate. a) What are the probabilities that all four of the girls were carriers of the allele hemophilia? b) Supposing Alexis had lived and married a normal woman, what are the chances that his daughter would be a hemophiliac? c) What are the chances his daughters would be carriers? d) What are the chances that his sons would be hemophiliacs? (4 points) B)Mr. Jones has type A blood. His wife has type AB blood. Their first child has type B blood. What are the possible phenotypes for future offspring and the probabilities for each one? (2 points) For both parts of Extra credit question – 6 points

Red-green color blindness People with intact color vision will see a 15. Someone with color deficient vision will see a 13 or 17 or nothing.

Everyone will see a “ 25”. People with normal vision will see a “ 29” whereas someone who is color blind will only see spots.

Genes located on alternative versions called (a) alleles chromosomes at specific locations called (b) loci if both same, if different, genotype called (c) homozygous heterozygous expressed allele called (d) dominant unexpressed allele called (e) recessive inheritance when phenotype In between called (f) incomplete dominance