* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download non-Mendelian inheritance
Therapeutic gene modulation wikipedia , lookup
Behavioral epigenetics wikipedia , lookup
Epigenetics wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Ridge (biology) wikipedia , lookup
Genome evolution wikipedia , lookup
Minimal genome wikipedia , lookup
Mitochondrial DNA wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Gene expression programming wikipedia , lookup
History of genetic engineering wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
X-inactivation wikipedia , lookup
Genome (book) wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Gene expression profiling wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Designer baby wikipedia , lookup
Genomic imprinting wikipedia , lookup
Transgenerational epigenetic inheritance wikipedia , lookup
Microevolution wikipedia , lookup
Genetics: Analysis and Principles Robert J. Brooker CHAPTER 7 NON-MENDELIAN INHERITANCE Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display INTRODUCTION • Mendelian inheritance patterns involve genes that – Directly influence the outcome of an organism’s traits and – Obey Mendel’s laws • Most genes in eukaryotic species follow a Mendelian pattern of inheritance – However, there are many that don’t • Linkage can be considered as non-Mendelian inheritance Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-2 INTRODUCTION • Patterns of inheritance that deviate from a Mendelian pattern: – Maternal effect and epigenetic inheritance • Involve genes in the nucleus – Extranuclear inheritance • Involves genes in organelles other than the nucleus – Mitochondria – Chloroplasts Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-3 7.1 MATERNAL EFFECT • Maternal effect refers to an inheritance pattern for certain nuclear genes in which the genotype of the mother directly determines the phenotype of her offspring • This phenomenon is due to the accumulation of gene products that the mother provides to her developing eggs Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-4 The first example of a maternal effect gene was discovered in the 1920s by Boycott He was studying morphological features of the water snail, Limnaea peregra In this species, the shell and internal organs can be arranged in one of two directions Right-handed (dextral) Left-handed (sinistral) The dextral orientation is more common and dominant The snail’s body plan curvature depends on the cleavage pattern of the egg immediately after fertilization Figure 7.1 describes Boycott’s experiment Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-5 Reciprocal cross reciprocal cross is a breeding experiment designed to test the role of parental sex on a given inheritance pattern. All parent organisms must be true breeding to properly carry out such an experiment. In one cross, a male expressing the trait of interest will be crossed with a female not expressing the trait. In the other, a female expressing the trait of interest will be crossed with a male not expressing the trait. A 3:1 phenotypic ratio would be predicted by a Mendelian pattern of inheritance Figure 7.1 7-6 Alfred Sturtevant later explained the inconsistency with Mendelian inheritance Snail coiling is due to a maternal effect gene that exists as dextral (D) and sinistral (d) alelles The phenotype of the offspring depended solely on the genotype of the mother His conclusions were drawn from the inheritance patterns of the F2 and F3 generations Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-7 CO 7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Parental generation Fig. 7.1(TE Art) DD dd dd DD F1 generation Dd All dextral F2 generation Dd All sinistral Males and females 1 DD 2 Dd 1 dd All dextral Cross to each other F3 generation Males and females 3 dextral 1 sinistral Note that the phenotype of each generation depends on the maternal genotype of the previous generation DD or Dd mothers produce dextral offspring dd mothers produce sinistral offspring The phenotype of the progeny is determined by the mother’s genotype NOT phenotype The genotypes of the father and offspring do not affect the phenotype of the offspring Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-9 The gene products are a reflection of the genotype of the mother They are transported to the cytoplasm of the oocyte where they persist for a significant time after the egg has been fertilized Thus influencing the early developmental stages of the embryo Figure 7.2 7-11 D gene products cause egg cleavage that promotes a right-handed body plan Figure 7.2 7-12 d gene products cause egg cleavage that promotes a lefthanded body plan Even if the egg is fertilized by sperm carrying the D allele The sperm’s genotype is irrelevant because the expression of the sperm’s gene would be too late Figure 7.2 7-13 Maternal effect genes encode RNA or proteins that play important roles in the early steps of embryogenesis For example Cell division Cleavage pattern In Drosophila, geneticists have identified several dozen maternal effect genes These have profound effects on the early stages of development Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-14 7.2 EPIGENETIC INHERITANCE • Epigenetic inheritance refers to a pattern in which a modification occurs to a nuclear gene or chromosome that alters gene expression – However, the expression is not permanently changed over the course of many generations • Epigenetic changes are caused by DNA and chromosomal modifications – These can occur during oogenesis, spermatogenesis or early embryonic development Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-15 Dosage Compensation • The purpose of dosage compensation is to offset differences in the number of active sex chromosomes • Dosage compensation has been studied extensively in mammals, Drosophila and Caenorhabditis elegans • Depending on the species, dosage compensation occurs via different mechanisms – Refer to Table 7.1 Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-16 7-17 Fig. 7.3 Barr body is a highly condensed X chromosome • The mechanism of X inactivation, also known as the Lyon hypothesis, is schematically illustrated in Figure 7.4 The example involves a white and black variegated coat color found in certain strains of mice A female mouse has inherited two X chromosomes One from its mother that carries an allele conferring white coat color (Xb) One from its father that carries an allele conferring black coat color (XB) Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-20 The epithelial cells derived from this embryonic cell will produce a patch of white fur At an early stage of embryonic development While those from this will produce a patch of black fur Figure 7.4 7-21 • During X chromosome inactivation, the DNA becomes highly compacted – Most genes on the inactivated X cannot be expressed • When this inactivated X is replicated during cell division – Both copies remain highly compacted and inactive • In a similar fashion, X inactivation is passed along to all future somatic cells • Another example of variegated coat color Is found in calico cats – Refer to Figure 7.3b Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-22 7.3 EXTRANUCLEAR INHERITANCE • Extranuclear inheritance refers to inheritance patterns involving genetic material outside the nucleus • The two most important examples: mitochondria and chloroplasts • These organelles are found in the cytoplasm – Extranuclear inheritance = cytoplasmic inheritance Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-54 • In general, mitochondrial genomes are – Fairly small in animals – Intermediate in size in fungi, algae and protists – Fairly large in plants Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-57 • The main function of mitochondria is oxidative phosphorylation – A process used to generate ATP (adenosine triphosphate) • ATP is used as an energy source to drive cellular reactions • The genetic material in mitochondria is referred to as mtDNA • The human mtDNA consists of only 17,000 bp (Figure 7.14) – It carries relatively few genes • rRNA and tRNA genes • 13 genes that function in oxidative phosphorylation • Note: Most mitochondrial proteins are encoded by genes in the nucleus – These proteins are made in the cytoplasm, then transported into the mitochondria Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display 7-58