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Genetic variants in parents may affect the fitness of their offspring, even if the child does not carry the allele. This indirect effect is referred to as “genetic nurture.” Kong et al. used data from genome-wide association studies of educational attainment to construct polygenic scores for parents that only considered the nontransmitted alleles (see the Perspective by Koellinger and Harden). The findings suggest that genetic nurture is ultimately due to genetic variation in the population and is mediated by the environment that parents create for their children. Science , this issue p. 424 ; see also p. 386 Behavioral genetics can transmit an environmental effect from parents and other related caregivers to their children. Sequence variants in the parental genomes that are not transmitted to a child (the proband) are often ignored in genetic studies. Here we show that nontransmitted alleles can affect a child through their impacts on the parents and other relatives, a phenomenon we call “genetic nurture.” Using results from a meta-analysis of educational attainment, we find that the polygenic score computed for the nontransmitted alleles of 21,637 probands with at least one parent genotyped has an estimated effect on the educational attainment of the proband that is 29.9% ( P = 1.6 × 10 −14 ) of that of the transmitted polygenic score. Genetic nurturing effects of this polygenic score extend to other traits. Paternal and maternal polygenic scores have similar effects on educational attainment, but mothers contribute more than fathers to nutrition- and heath-related traits.

Genetic recombination is an essential process in generating genetic diversity. Recombination occurs both through the shuffling of maternal and paternal chromosomes and through mutations generated by resolution of the physical breaks necessary for this process. Halldorsson et al. sequenced the full genomes of parents and offspring to create a map of human recombination and estimate the relationship with de novo mutations. Interestingly, transcribed regions of the genome were less likely to have crossovers, suggesting that there may be selection to reduce changes in genetic sequences via recombination or mutation in these regions. Science , this issue p. eaau1043 A high-resolution human genetic map from whole genomes identifies patterns of recombination and de novo mutation. Genetic diversity arises from recombination and de novo mutation (DNM). Using a combination of microarray genotype and whole-genome sequence data on parent-child pairs, we identified 4,531,535 crossover recombinations and 200,435 DNMs. The resulting genetic map has a resolution of 682 base pairs. Crossovers exhibit a mutagenic effect, with overrepresentation of DNMs within 1 kilobase of crossovers in males and females. In females, a higher mutation rate is observed up to 40 kilobases from crossovers, particularly for complex crossovers, which increase with maternal age. We identified 35 loci associated with the recombination rate or the location of crossovers, demonstrating extensive genetic control of meiotic recombination, and our results highlight genes linked to the formation of the synaptonemal complex as determinants of crossovers.

The corneal endothelium is vital for transparency and proper hydration of the cornea. Here, we conduct a genome-wide association study of corneal endothelial cell density (cells/mm 2 ), coefficient of cell size variation (CV), percentage of hexagonal cells (HEX) and central corneal thickness (CCT) in 6,125 Icelanders and find associations at 10 loci, including 7 novel. We assess the effects of these variants on various ocular biomechanics such as corneal hysteresis (CH), as well as eye diseases such as glaucoma and corneal dystrophies. Most notably, an intergenic variant close to ANAPC1 (rs78658973[A], frequency = 28.3%) strongly associates with decreased cell density and accounts for 24% of the population variance in cell density (β = −0.77 SD, P  = 1.8 × 10 −314 ) and associates with increased CH (β = 0.19 SD, P  = 2.6 × 10 −19 ) without affecting risk of corneal diseases and glaucoma. Our findings indicate that despite correlations between cell density and eye diseases, low cell density does not increase the risk of disease. The corneal endothelium is crucial for proper vision. Here, Ivarsdottir et al. perform genome-wide association studies for various corneal endothelial cell measurements and find that an intergenic variant near ANAPC1 explains 24% of the variance of endothelial cell density and associates with corneal hysteresis.

Mutations generate sequence diversity and provide a substrate for selection. The rate of de novo mutations is therefore of major importance to evolution. Here we conduct a study of genome-wide mutation rates by sequencing the entire genomes of 78 Icelandic parent–offspring trios at high coverage. We show that in our samples, with an average father’s age of 29.7, the average de novo mutation rate is 1.20 × 10 −8 per nucleotide per generation. Most notably, the diversity in mutation rate of single nucleotide polymorphisms is dominated by the age of the father at conception of the child. The effect is an increase of about two mutations per year. An exponential model estimates paternal mutations doubling every 16.5 years. After accounting for random Poisson variation, father’s age is estimated to explain nearly all of the remaining variation in the de novo mutation counts. These observations shed light on the importance of the father’s age on the risk of diseases such as schizophrenia and autism. Whole-genome sequencing of 78 Icelandic parent–offspring trios is used to study the de novo mutation rate at the genome-wide level; the rate is shown to increase by about two mutations a year as a function of the increasing age of the father at conception, highlighting the importance of father’s age on the risk of diseases such as autism and schizophrenia. Fathers' ages linked to disease risk De novo mutations are important both as sources of diversity in evolution and for their immediate impact on diseases. Scientists at deCODE genetics and their colleagues have used whole-genome sequencing data from 78 Icelandic parent–offspring trios to study mutation rates in humans at the genome-wide level. They find that diversity in the mutation rate of single nucleotide polymorphisms is dominated by the age of the father at the time a child is conceived. For each year increase in the father's age at conception, the number of mutations increases by about two, and once the effects of random variation are accounted for the father's age is estimated to explain almost all of the remaining variation in the de novo mutation counts. Furthermore, the results show that demographic transitions that affect the age at which males reproduce can have a considerable effect on the rate of mutations, and consequently on the risk of diseases such as schizophrenia and autism.

Mutation of the DNA molecule is one of the most fundamental processes in biology. In this study, we use 283 parent-offspring trios to estimate the rate of mutation for both single nucleotide variants (SNVs) and short length variants (indels) in humans and examine the mutation process. We found 17812 SNVs, corresponding to a mutation rate of 1.29 × 10-8 per position per generation (PPPG) and 1282 indels corresponding to a rate of 9.29 × 10-10 PPPG. We estimate that around 3% of human de novo SNVs are part of a multi-nucleotide mutation (MNM), with 558 (3.1%) of mutations positioned less than 20kb from another mutation in the same individual (median distance of 525bp). The rate of de novo mutations is greater in late replicating regions (p = 8.29 × 10-19) and nearer recombination events (p = 0.0038) than elsewhere in the genome.

Bjarni Halldorsson, Kari Stefansson and colleagues use SNP array and whole-genome sequencing data to estimate the meiotic gene conversion rate ( G ) in humans. They find that G for SNPs is 7.0 conversions/Mb per generation, is 2.17 greater in mothers than in fathers, and increases with maternal age. Meiotic recombination involves a combination of gene conversion and crossover events that, along with mutations, produce germline genetic diversity. Here we report the discovery of 3,176 SNP and 61 indel gene conversions. Our estimate of the non-crossover (NCO) gene conversion rate ( G ) is 7.0 for SNPs and 5.8 for indels per megabase per generation, and the GC bias is 67.6%. For indels, we demonstrate a 65.6% preference for the shorter allele. NCO gene conversions from mothers are longer than those from fathers, and G is 2.17 times greater in mothers. Notably, G increases with the age of mothers, but not the age of fathers. A disproportionate number of NCO gene conversions in older mothers occur outside double-strand break (DSB) regions and in regions with relatively low GC content. This points to age-related changes in the mechanisms of meiotic gene conversion in oocytes.

Patrick Sulem, Hannes Helgason and colleagues identify homozygous and compound heterozygous loss-of-function variants of minor allele frequency <2% in 7.7% of the genotyped Icelandic population. Under transmission of some of these variants from heterozygous parents provides evidence that they are actually deleterious. Loss-of-function mutations cause many mendelian diseases. Here we aimed to create a catalog of autosomal genes that are completely knocked out in humans by rare loss-of-function mutations. We sequenced the whole genomes of 2,636 Icelanders and imputed the sequence variants identified in this set into 101,584 additional chip-genotyped and phased Icelanders. We found a total of 6,795 autosomal loss-of-function SNPs and indels in 4,924 genes. Of the genotyped Icelanders, 7.7% are homozygotes or compound heterozygotes for loss-of-function mutations with a minor allele frequency (MAF) below 2% in 1,171 genes (complete knockouts). Genes that are highly expressed in the brain are less often completely knocked out than other genes. Homozygous loss-of-function offspring of two heterozygous parents occurred less frequently than expected (deficit of 136 per 10,000 transmissions for variants with MAF <2%, 95% confidence interval (CI) = 10–261).

Recombination maps reveal differences between the sexes High-resolution recombination maps serve many purposes in genetic research. The currently available maps, which use linkage disequilibrium patterns of high-density SNP (single nucleotide polymorphism) data from the HapMap project, have proved to be very useful. But they have some limitations; for instance, they do not provide information on differences in recombination characteristics between and within the sexes. A team at biopharmaceutical firm deCODE genetics in Reykjavik has used genome-wide SNP data from more than 15,000 parent–offspring pairs to construct the first recombination maps based on directly observed recombination events, providing resolution down to 10 kilobases. Their data reveal interesting recombination differences between the sexes. In males, for example, recombination tends to shuffle exons, whereas in females it generates new combinations of nearby genes. Comparisons of these maps with those based on linkage disequilibrium reveal previously unrecognized differences between populations in Europe, Africa and the United States. Here, human genome-wide single-nucleotide polymorphism (SNP) data from more than 15,000 parent–offspring pairs have been used to construct the first recombination maps that are based on directly observed recombination events. The data reveal interesting differences between the sexes: for instance, in males recombination tends to shuffle exons, whereas in females it generates new combinations of nearby genes. Comparison of these maps with others also reveals population differences. Meiotic recombinations contribute to genetic diversity by yielding new combinations of alleles. Recently, high-resolution recombination maps were inferred from high-density single-nucleotide polymorphism (SNP) data using linkage disequilibrium (LD) patterns that capture historical recombination events 1 , 2 . The use of these maps has been demonstrated by the identification of recombination hotspots 2 and associated motifs 3 , and the discovery that the PRDM9 gene affects the proportion of recombinations occurring at hotspots 4 , 5 , 6 . However, these maps provide no information about individual or sex differences. Moreover, locus-specific demographic factors like natural selection 7 can bias LD-based estimates of recombination rate. Existing genetic maps based on family data avoid these shortcomings 8 , but their resolution is limited by relatively few meioses and a low density of markers. Here we used genome-wide SNP data from 15,257 parent–offspring pairs to construct the first recombination maps based on directly observed recombinations with a resolution that is effective down to 10 kilobases (kb). Comparing male and female maps reveals that about 15% of hotspots in one sex are specific to that sex. Although male recombinations result in more shuffling of exons within genes, female recombinations generate more new combinations of nearby genes. We discover novel associations between recombination characteristics of individuals and variants in the PRDM9 gene and we identify new recombination hotspots. Comparisons of our maps with two LD-based maps inferred from data of HapMap populations of Utah residents with ancestry from northern and western Europe (CEU) and Yoruba in Ibadan, Nigeria (YRI) reveal population differences previously masked by noise and map differences at regions previously described as targets of natural selection.

This study implicates five genetic loci in bone mineral density. Two of these loci are new; three implicate genes known to be involved in bone remodeling, such as the receptor activator of nuclear factor-κB ligand gene ( RANKL ). Analyses showed that three of the loci are associated with osteoporotic fracture. This study implicates five genetic loci in bone mineral density. Two of these loci are new; three implicate genes known to be involved in bone remodeling. Osteoporosis confers substantive morbidity and mortality and associated costs and predisposes people to fragility fractures at the hip, spine, forearm, or other skeletal sites. 1 It is a common disease affecting both sexes in populations of various ancestries, although elderly women of European descent are at the highest risk. 2 Bone density is the single best predictor of osteoporotic fractures and is a valuable tool in evaluation of the risk of fractures. 3 , 4 There is abundant evidence for a genetic contribution to variation in bone mineral density, with heritability estimates between 0.6 and 0.8. 5 Bone mineral density is also influenced by environmental . . .

John Perry, Ken Ong and colleagues perform a genome-wide association study for reproductive ability, behavior and success to determine underlying genetic factors. They find 38 variants associated with age of first sexual intercourse and show that both physical and neurobehavioral traits influence the onset of reproductive activity. The ages of puberty, first sexual intercourse and first birth signify the onset of reproductive ability, behavior and success, respectively. In a genome-wide association study of 125,667 UK Biobank participants, we identify 38 loci associated ( P < 5 × 10 −8 ) with age at first sexual intercourse. These findings were taken forward in 241,910 men and women from Iceland and 20,187 women from the Women's Genome Health Study. Several of the identified loci also exhibit associations ( P < 5 × 10 −8 ) with other reproductive and behavioral traits, including age at first birth (variants in or near ESR1 and RBM6 – SEMA3F ), number of children ( CADM2 and ESR1 ), irritable temperament ( MSRA ) and risk-taking propensity ( CADM2 ). Mendelian randomization analyses infer causal influences of earlier puberty timing on earlier first sexual intercourse, earlier first birth and lower educational attainment. In turn, likely causal consequences of earlier first sexual intercourse include reproductive, educational, psychiatric and cardiometabolic outcomes.