Department of Genetics, University of Alabama at Birmingham,. 3rd Avenue , South The basic unit of genetic function is the gene, the chemical basis for which is the DNA .. and genes and for many years was published in book form. Department of Genetic Medicine and Development publishers, felt that the book should be continued with a new fourth edition in the. of 'Genetics and Genomics' held in Semmelweis University for medical, pharmacological The book does not contain basic genetics and molecular biology.
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Her research interests include gene regulation and the genetic control of cellular form. Composition and Book Layout: Thompson Steele, Inc. Prepress. It's a history book - a narrative of the journey of our species through time. It's a shop manual, with an incredibly detailed blueprint for building every human cell. Detecting human disease alleles: molecular genetic diagnostics. Genetic tion in Chapter 20, but for the greater part of the book, we shall be.
What should babies be screened for, and who should share in the data? Social inequality gapes, exacerbated by climate change, driving hostility towards immigrants and flares of militant racism. At such a juncture, yet another expression of the discredited, simplistic idea that genes alone control human nature seems particularly insidious. And yet, here we are again with Blueprint, by educational psychologist Robert Plomin. Crude hereditarianism often re-emerges after major advances in biological knowledge: Darwinism begat eugenics; Mendelism begat worse eugenics. The flowering of medical genetics in the s led to the notorious, now-debunked idea that men with an extra Y chromosome XYY genotype were prone to violence.
When studying human genetic diseases, geneticists often use pedigree charts to represent the inheritance of traits. Multiple gene interactions[ edit ] Human height is a trait with complex genetic causes. Francis Galton 's data from shows the relationship between offspring height as a function of mean parent height.
Organisms have thousands of genes, and in sexually reproducing organisms these genes generally assort independently of each other.
This means that the inheritance of an allele for yellow or green pea color is unrelated to the inheritance of alleles for white or purple flowers.
This phenomenon, known as " Mendel's second law " or the "law of independent assortment," means that the alleles of different genes get shuffled between parents to form offspring with many different combinations. Some genes do not assort independently, demonstrating genetic linkage , a topic discussed later in this article. Often different genes can interact in a way that influences the same trait. In the Blue-eyed Mary Omphalodes verna , for example, there exists a gene with alleles that determine the color of flowers: blue or magenta.
Another gene, however, controls whether the flowers have color at all or are white. When a plant has two copies of this white allele, its flowers are white—regardless of whether the first gene has blue or magenta alleles.
This interaction between genes is called epistasis , with the second gene epistatic to the first. These complex traits are products of many genes. The degree to which an organism's genes contribute to a complex trait is called heritability.
For example, human height is a trait with complex causes. Bases pair through the arrangement of hydrogen bonding between the strands. The molecular basis for genes is deoxyribonucleic acid DNA. DNA is composed of a chain of nucleotides , of which there are four types: adenine A , cytosine C , guanine G , and thymine T.
Genetic information exists in the sequence of these nucleotides, and genes exist as stretches of sequence along the DNA chain. DNA normally exists as a double-stranded molecule, coiled into the shape of a double helix. Thus, in its two-stranded form, each strand effectively contains all necessary information, redundant with its partner strand.
This structure of DNA is the physical basis for inheritance: DNA replication duplicates the genetic information by splitting the strands and using each strand as a template for synthesis of a new partner strand. In bacteria , each cell usually contains a single circular genophore , while eukaryotic organisms such as plants and animals have their DNA arranged in multiple linear chromosomes.
These DNA strands are often extremely long; the largest human chromosome, for example, is about million base pairs in length.
While haploid organisms have only one copy of each chromosome, most animals and many plants are diploid , containing two of each chromosome and thus two copies of every gene. Walther Flemming 's diagram of eukaryotic cell division. Chromosomes are copied, condensed, and organized. Then, as the cell divides, chromosome copies separate into the daughter cells. Many species have so-called sex chromosomes that determine the gender of each organism.
In evolution, this chromosome has lost most of its content and also most of its genes, while the X chromosome is similar to the other chromosomes and contains many genes.
The X and Y chromosomes form a strongly heterogeneous pair. Main articles: Asexual reproduction and Sexual reproduction When cells divide, their full genome is copied and each daughter cell inherits one copy. This process, called mitosis , is the simplest form of reproduction and is the basis for asexual reproduction.
Asexual reproduction can also occur in multicellular organisms, producing offspring that inherit their genome from a single parent. Offspring that are genetically identical to their parents are called clones.
Eukaryotic organisms often use sexual reproduction to generate offspring that contain a mixture of genetic material inherited from two different parents. The process of sexual reproduction alternates between forms that contain single copies of the genome haploid and double copies diploid.
Diploid organisms form haploids by dividing, without replicating their DNA, to create daughter cells that randomly inherit one of each pair of chromosomes. Most animals and many plants are diploid for most of their lifespan, with the haploid form reduced to single cell gametes such as sperm or eggs. Some bacteria can undergo conjugation , transferring a small circular piece of DNA to another bacterium.
Recombination and genetic linkage[ edit ] Main articles: Chromosomal crossover and Genetic linkage Thomas Hunt Morgan 's illustration of a double crossover between chromosomes.
With Charles Davenport, a prominent US eugenicist, whispering in his ear, Goddard suggested that learning disabilities resulted from a single Mendelian recessive gene. When he factored in behaviours thought to result from that condition — such as criminality and promiscuity — the alleged association went sky-high. He never seems to have questioned whether a single gene for such a complex trait made sense biologically.
No one is so foolish as to believe in a single gene for learning disability any more. As has been well established, the genetic contribution to complex traits is spread over many genes, each contributing a minuscule sliver of the variability for the trait.
A polygenic score is a correlation coefficient.
The SNPs are markers only. Although they might, in some cases, suggest genomic neighbourhoods in which to search for genes that directly affect the trait, the polygenic score itself is in no sense causal.
Plomin understands this and says so repeatedly in the book — yet contradicts himself several times by arguing that the scores are, in fact, causal. If all you have is a polygenic score, everything looks like a gene. Polygenic scores do suggest some things to cheer about. We should applaud the broad-based shift across biomedicine from monogenic to polygenic causation.
The method is finding wide application, from precision medicine to field biology. For example, polygenic scores have been shown to improve risk predictions for prostate, ovarian and breast cancers. They can point to traits that might have been influenced by local adaptation, and gauge the pace of evolutionary change. He argues that we should think of personality traits as we do autism or attention-deficit hyperactivity disorder: as existing on spectra.
In a book so filled with retrograde ideas about genes, I was pleasantly surprised to find this strong, welcome biological support for the idea of neurodiversity.
In , educational psychologist Arthur Jensen dropped a pseudo-statistical bombshell in the Harvard Educational Review. He argued that genetics was responsible for the notional IQ gap between African Americans and white people not bias baked into the test or environmental effects and that remedial education was pointless. Blueprint uses language, imagery, rhetoric, conclusions and numbers that will be familiar to readers who have, like me, slogged through all these works.
A sobering theme of most, Blueprint included, is their aspiration of shaping social policy. Like much of that literature, Blueprint plays fast and loose with the concept of heritability. Sometimes Plomin treats it correctly as a variable property of a population in a given environment.