recessive What causes PKU PKU is caused by

recessive

What causes PKU? PKU is caused by mutations in the gene that helps make an enzyme called phenylalanine hydroxylase. This enzyme is needed to convert the amino acid phenylalanine into other substances the body needs. How is it treated? People with PKU need to follow a diet that limits foods with phenylalanine. The diet should be followed carefully and be started as soon after birth as possible. In the past, experts believed that it was safe for people to stop following the diet as they got older. However, they now recommend that people with PKU stay on the diet throughout their lives for better physical and mental health. It is especially important for a pregnant woman with PKU to strictly follow the low-phenylalanine diet throughout her pregnancy to ensure the healthy development of her infant.

Sickle-Cell Disease Recessive? Dominant? Codominant? • Sickle-cell disease affects one out of 400 African. Americans • The disease is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells • Symptoms include physical weakness, pain, organ damage, and even paralysis Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Sickle Cell Anemia Sickle cell disease is more common in certain ethnic groups, including: People of African descent, including African-Americans (among whom 1 in 12 carries a sickle cell gene) Hispanic-Americans from Central and South America. People of Middle Eastern, Asian, Indian, and Mediterranean descent.

Fig. 14 -UN 2 Degree of dominance Complete dominance of one allele Example Description Heterozygous phenotype PP same as that of homozygous dominant Pp Incomplete dominance Heterozygous phenotype intermediate between of either allele the two homozygous phenotypes CR CR CR CW CW CW Codominance Heterozygotes: Both phenotypes expressed Multiple alleles In the whole population, ABO blood group alleles some genes have more IA , I B , i than two alleles Pleiotropy One gene is able to affect multiple phenotypic characters IA IB Sickle-cell disease

polydactyly Frequency of Dominant Alleles • Dominant alleles are not necessarily more common in populations than recessive alleles • For example, one baby out of 400 in the United States is born with extra fingers or toes Photos: e. Hand. com (the electronic textbook for hand surgery) Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Blood Typing Problem

Concept 15. 2: Sex-linked genes exhibit unique patterns of inheritance In humans and some other animals, there is a chromosomal basis of sex determination Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Females are XX, and males are XY Each ovum contains an X chromosome, while a sperm may contain either an X or a Y chromosome Other animals have different methods of sex determination Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Inheritance of Sex-Linked Genes The sex chromosomes have genes for many characters unrelated to sex A gene located on either sex chromosome is called a sex-linked gene In humans, sex-linked usually refers to a gene on the larger X chromosome Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Sex-linked genes follow specific patterns of inheritance For a recessive sex-linked trait to be expressed A female needs two copies of the allele A male needs only one copy of the allele Sex-linked recessive disorders are much more common in males than in females Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Fig. 15 -5 X Y

Barr body – an inactivated X chromosome in each of a female’s diploid cells.

Correlating Behavior of a Gene’s Alleles with Behavior of a Chromosome Pair In one experiment, Morgan mated male flies with white eyes (mutant) with female flies with red eyes (wild type) The F 1 generation all had red eyes The F 2 generation showed the 3: 1 red: white eye ratio, but only males had white eyes Morgan determined that the white-eyed mutant allele must be located on the X chromosome Morgan’s finding supported the chromosome theory of inheritance Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

The Chromosomal Basis of Sex In humans and other mammals, there are two varieties of sex chromosomes: a larger X chromosome and a smaller Y chromosome Only the ends of the Y chromosome have regions that are homologous with the X chromosome The SRY gene on the Y chromosome codes for the development of testes Copyright © 2008 Pearson Education Inc. , publishing as Pearson Benjamin Cummings

Fig. 26. 14 b Sex-linked recessive

Sex-linked recessive pingrybiology. pbwiki. com www. kelleycom. com Hemophilia is a rare, inherited bleeding disorder in which blood doesn’t clot normally. People with hemophilia may bleed for a longer time than others after an injury. Individuals with the disorder may bleed internally, especially in knees, ankles, and elbows. This bleeding can damage organs or tissues and, sometimes, be fatal.

Photo: www. freewebs. com/georgeromanov/Foto%201913. jpg

The European Royal Family

Color Blindness some forms are Sex-linked

Fig. 26. 18 Human X Chromosome disorders

Polygenic traits – more than 1 gene controlling a single trait

Example of Polygenic Problem: Skin Color (oversimplification – only using 2 genes. There actually more involved) MC MC Mc MMCC MMCc mc Mm. CC mc Mm. Cc M = lots of melanin m= less melanin C=lots of cells C=less cells Mc MMCc MMcc m. C Mm. Cc Mmcc Female = Mm. Cc Male = Mm. Cc Phenotypes: Mm. CC Mm. Cc mm. CC mm. Cc Mmcc mm. Cc mmcc Very dark: Dark: Medium: Light: Very light: 1 4 6 4 1

Graphing Skin Tone Results 6 # of individuals 4 in pop. 1 VD D M L VL

Human Bell Shaped Curve